Intercomparison of 3D pore-scale flow and solute transport simulation methods

DOE PAGES

Mehmani, Yashar; Schoenherr, Martin; Pasquali, Andrea; ...

2015-09-28

Multiple numerical approaches have been developed to simulate porous media fluid flow and solute transport at the pore scale. These include 1) methods that explicitly model the three-dimensional geometry of pore spaces and 2) methods that conceptualize the pore space as a topologically consistent set of stylized pore bodies and pore throats. In previous work we validated a model of the first type, using computational fluid dynamics (CFD) codes employing a standard finite volume method (FVM), against magnetic resonance velocimetry (MRV) measurements of pore-scale velocities. Here we expand that validation to include additional models of the first type based onmore » the lattice Boltzmann method (LBM) and smoothed particle hydrodynamics (SPH), as well as a model of the second type, a pore-network model (PNM). The PNM approach used in the current study was recently improved and demonstrated to accurately simulate solute transport in a two-dimensional experiment. While the PNM approach is computationally much less demanding than direct numerical simulation methods, the effect of conceptualizing complex three-dimensional pore geometries on solute transport in the manner of PNMs has not been fully determined. We apply all four approaches (FVM-based CFD, LBM, SPH and PNM) to simulate pore-scale velocity distributions and (for capable codes) nonreactive solute transport, and intercompare the model results. Comparisons are drawn both in terms of macroscopic variables (e.g., permeability, solute breakthrough curves) and microscopic variables (e.g., local velocities and concentrations). Generally good agreement was achieved among the various approaches, but some differences were observed depending on the model context. The intercomparison work was challenging because of variable capabilities of the codes, and inspired some code enhancements to allow consistent comparison of flow and transport simulations across the full suite of methods. This paper provides support for confidence in a variety of pore-scale modeling methods and motivates further development and application of pore-scale simulation methods.« less

Application Of Positron Beams For The Characterization Of Nano-scale Pores In Thin Films

NASA Astrophysics Data System (ADS)

Hirata, K.; Ito, K.; Kobayashi, Y.; Suzuki, R.; Ohdaira, T.; Eijt, S. W. H.; Schut, H.; van Veen, A.

2003-08-01

We applied three positron annihilation techniques, positron 3γ-annihilation spectroscopy, positron annihilation lifetime spectroscopy, and angular correlation of annihilation radiation, to the characterization of nano-scale pores in thin films by combining them with variable-energy positron beams. Characterization of pores in thin films is an important part of the research on various thin films of industrial importance. The results of our recent studies on pore characterization of thin films by positron beams will be reported here.

Finite-difference method Stokes solver (FDMSS) for 3D pore geometries: Software development, validation and case studies

NASA Astrophysics Data System (ADS)

Gerke, Kirill M.; Vasilyev, Roman V.; Khirevich, Siarhei; Collins, Daniel; Karsanina, Marina V.; Sizonenko, Timofey O.; Korost, Dmitry V.; Lamontagne, Sébastien; Mallants, Dirk

2018-05-01

Permeability is one of the fundamental properties of porous media and is required for large-scale Darcian fluid flow and mass transport models. Whilst permeability can be measured directly at a range of scales, there are increasing opportunities to evaluate permeability from pore-scale fluid flow simulations. We introduce the free software Finite-Difference Method Stokes Solver (FDMSS) that solves Stokes equation using a finite-difference method (FDM) directly on voxelized 3D pore geometries (i.e. without meshing). Based on explicit convergence studies, validation on sphere packings with analytically known permeabilities, and comparison against lattice-Boltzmann and other published FDM studies, we conclude that FDMSS provides a computationally efficient and accurate basis for single-phase pore-scale flow simulations. By implementing an efficient parallelization and code optimization scheme, permeability inferences can now be made from 3D images of up to 109 voxels using modern desktop computers. Case studies demonstrate the broad applicability of the FDMSS software for both natural and artificial porous media.

Pore and Continuum Scale Study of the Effect of Subgrid Transport Heterogeneity on Redox Reaction Rates

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Yuanyuan; Liu, Chongxuan; Zhang, Changyong

2015-08-01

A micromodel system with a pore structure for heterogeneous flow and transport was used to investigate the effect of subgrid transport heterogeneity on redox reaction rates. Hematite reductive dissolution by injecting a reduced form of flavin mononucleotide (FMNH2) at variable flow rates was used as an example to probe the variations of redox reaction rates in different subgrid transport domains. Experiments, pore-scale simulations, and macroscopic modeling were performed to measure and simulate in-situ hematite reduction and to evaluate the scaling behavior of the redox reaction rates from the pore to macroscopic scales. The results indicated that the measured pore-scale ratesmore » of hematite reduction were consistent with the predictions from a pore scale reactive transport model. A general trend is that hematite reduction followed reductant transport pathways, starting from the advection-dominated pores toward the interior of diffusion-dominated domains. Two types of diffusion domains were considered in the micromodel: a micropore diffusion domain, which locates inside solid grains or aggregates where reactant transport is limited by diffusion; and a macropore diffusion domain, which locates at wedged, dead-end pore spaces created by the grain-grain contacts. The rate of hematite reduction in the advection-dominated domain was faster than those in the diffusion-controlled domains, and the rate in the macropore diffusion domain was faster than that in the micropore domain. The reduction rates in the advection and macropore diffusion domains increased with increasing flow rate, but were affected by different mechanisms. The rate increase in the advection domain was controlled by the mass action effect as a faster flow supplied more reactants, and the rate increase in the macropore domain was more affected by the rate of mass exchange with the advection domain, which increased with increasing flow rate. The hematite reduction rate in the micropore domain was, however, not affected by the flow rate because molecular diffusion limits reductant supply to the micropore domain interior. Domain-based macroscopic models were evaluated to scale redox reaction rates from the pore to macroscopic scales. A single domain model, which ignores subgrid transport heterogeneity deviated significantly from the pore-scale results. Further analysis revealed that the rate expression for hematite reduction was not scalable from the pore to porous media using the single domain model. A three-domain model, which effectively considers subgrid reactive diffusion in the micropore and macropore domains, significantly improved model description. Overall this study revealed the importance of subgrid transport heterogeneity in the manifestation of redox reaction rates in porous media and in scaling reactions from the pore to porous media. The research also supported that the domain-based scaling approach can be used to directly scale redox reactions in porous media with subgrid transport heterogeneity.« less

Nanometer-Scale Pore Characteristics of Lacustrine Shale, Songliao Basin, NE China

PubMed Central

Wang, Min; Yang, Jinxiu; Wang, Zhiwei; Lu, Shuangfang

2015-01-01

In shale, liquid hydrocarbons are accumulated mainly in nanometer-scale pores or fractures, so the pore types and PSDs (pore size distributions) play a major role in the shale oil occurrence (free or absorbed state), amount of oil, and flow features. The pore types and PSDs of marine shale have been well studied; however, research on lacustrine shale is rare, especially for shale in the oil generation window, although lacustrine shale is deposited widely around the world. To investigate the relationship between nanometer-scale pores and oil occurrence in the lacustrine shale, 10 lacustrine shale core samples from Songliao Basin, NE China were analyzed. Analyses of these samples included geochemical measurements, SEM (scanning electron microscope) observations, low pressure CO2 and N2 adsorption, and high-pressure mercury injection experiments. Analysis results indicate that: (1) Pore types in the lacustrine shale include inter-matrix pores, intergranular pores, organic matter pores, and dissolution pores, and these pores are dominated by mesopores and micropores; (2) There is no apparent correlation between pore volumes and clay content, however, a weak negative correlation is present between total pore volume and carbonate content; (3) Pores in lacustrine shale are well developed when the organic matter maturity (Ro) is >1.0% and the pore volume is positively correlated with the TOC (total organic carbon) content. The statistical results suggest that oil in lacustrine shale mainly occurs in pores with diameters larger than 40 nm. However, more research is needed to determine whether this minimum pore diameter for oil occurrence in lacustrine shale is widely applicable. PMID:26285123

Nanometer-Scale Pore Characteristics of Lacustrine Shale, Songliao Basin, NE China.

PubMed

Wang, Min; Yang, Jinxiu; Wang, Zhiwei; Lu, Shuangfang

2015-01-01

In shale, liquid hydrocarbons are accumulated mainly in nanometer-scale pores or fractures, so the pore types and PSDs (pore size distributions) play a major role in the shale oil occurrence (free or absorbed state), amount of oil, and flow features. The pore types and PSDs of marine shale have been well studied; however, research on lacustrine shale is rare, especially for shale in the oil generation window, although lacustrine shale is deposited widely around the world. To investigate the relationship between nanometer-scale pores and oil occurrence in the lacustrine shale, 10 lacustrine shale core samples from Songliao Basin, NE China were analyzed. Analyses of these samples included geochemical measurements, SEM (scanning electron microscope) observations, low pressure CO2 and N2 adsorption, and high-pressure mercury injection experiments. Analysis results indicate that: (1) Pore types in the lacustrine shale include inter-matrix pores, intergranular pores, organic matter pores, and dissolution pores, and these pores are dominated by mesopores and micropores; (2) There is no apparent correlation between pore volumes and clay content, however, a weak negative correlation is present between total pore volume and carbonate content; (3) Pores in lacustrine shale are well developed when the organic matter maturity (Ro) is >1.0% and the pore volume is positively correlated with the TOC (total organic carbon) content. The statistical results suggest that oil in lacustrine shale mainly occurs in pores with diameters larger than 40 nm. However, more research is needed to determine whether this minimum pore diameter for oil occurrence in lacustrine shale is widely applicable.

Microfluidic Experiments Studying Pore Scale Interactions of Microbes and Geochemistry

NASA Astrophysics Data System (ADS)

Chen, M.; Kocar, B. D.

2016-12-01

Understanding how physical phenomena, chemical reactions, and microbial behavior interact at the pore-scale is crucial to understanding larger scale trends in groundwater chemistry. Recent studies illustrate the utility of microfluidic devices for illuminating pore-scale physical-biogeochemical processes and their control(s) on the cycling of iron, uranium, and other important elements 1-3. These experimental systems are ideal for examining geochemical reactions mediated by microbes, which include processes governed by complex biological phenomenon (e.g. biofilm formation, etc.)4. We present results of microfluidic experiments using a model metal reducing bacteria and varying pore geometries, exploring the limitations of the microorganisms' ability to access tight pore spaces, and examining coupled biogeochemical-physical controls on the cycling of redox sensitive metals. Experimental results will provide an enhanced understanding of coupled physical-biogeochemical processes transpiring at the pore-scale, and will constrain and compliment continuum models used to predict and describe the subsurface cycling of redox-sensitive elements5. 1. Vrionis, H. A. et al. Microbiological and geochemical heterogeneity in an in situ uranium bioremediation field site. Appl. Environ. Microbiol. 71, 6308-6318 (2005). 2. Pearce, C. I. et al. Pore-scale characterization of biogeochemical controls on iron and uranium speciation under flow conditions. Environ. Sci. Technol. 46, 7992-8000 (2012). 3. Zhang, C., Liu, C. & Shi, Z. Micromodel investigation of transport effect on the kinetics of reductive dissolution of hematite. Environ. Sci. Technol. 47, 4131-4139 (2013). 4. Ginn, T. R. et al. Processes in microbial transport in the natural subsurface. Adv. Water Resour. 25, 1017-1042 (2002). 5. Scheibe, T. D. et al. Coupling a genome-scale metabolic model with a reactive transport model to describe in situ uranium bioremediation. Microb. Biotechnol. 2, 274-286 (2009).

Measurements of pore-scale flow through apertures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chojnicki, Kirsten

Pore-scale aperture effects on flow in pore networks was studied in the laboratory to provide a parameterization for use in transport models. Four cases were considered: regular and irregular pillar/pore alignment with and without an aperture. The velocity field of each case was measured and simulated, providing quantitatively comparable results. Two aperture effect parameterizations were considered: permeability and transmission. Permeability values varied by an order of magnitude between the cases with and without apertures. However, transmission did not correlate with permeability. Despite having much greater permeability the regular aperture case permitted less transmission than the regular case. Moreover, both irregularmore » cases had greater transmission than the regular cases, a difference not supported by the permeabilities. Overall, these findings suggest that pore-scale aperture effects on flow though a pore-network may not be adequately captured by properties such as permeability for applications that are interested in determining particle transport volume and timing.« less

Pore-scale dynamics of enzyme adsorption, swelling and reactive dissolution determine sugar yield in hemicellulose hydrolysis for biofuel production

PubMed Central

Dutta, Sajal Kanti; Chakraborty, Saikat

2016-01-01

Hemicelluloses are the earth’s second most abundant structural polymers, found in lignocellulosic biomass. Efficient enzymatic depolymerization of xylans by cleaving their β-(1 → 4)-glycosidic bonds to produce soluble sugars is instrumental to the cost-effective production of liquid biofuels. Here we show that the multi-scale two-phase process of enzymatic hydrolysis of amorphous hemicelluloses is dominated by its smallest scale–the pores. In the crucial first five hours, two to fourfold swelling of the xylan particles allow the enzymes to enter the pores and undergo rapid non-equilibrium adsorption on the pore surface before they hydrolyze the solid polymers, albeit non-competitively inhibited by the products xylose and xylobiose. Rapid pore-scale reactive dissolution increases the solid carbohydrate’s porosity to 80–90%. This tightly coupled experimental and theoretical study quantifies the complex temporal dynamics of the transport and reaction processes coupled across scales and phases to show that this unique pore-scale phenomenon can be exploited to accelerate the depolymerization of hemicelluloses to monomeric sugars in the first 5–6 h. We find that an ‘optimal substrate loading’ of 5 mg/ml (above which substrate inhibition sets in) accelerates non-equilibrium enzyme adsorption and solid hemicellulose depolymerization at the pore-scale, which contributes three-quarters of the soluble sugars produced for bio-alcohol fermentation. PMID:27905534

Impact of spatially correlated pore-scale heterogeneity on drying porous media

NASA Astrophysics Data System (ADS)

Borgman, Oshri; Fantinel, Paolo; Lühder, Wieland; Goehring, Lucas; Holtzman, Ran

2017-07-01

We study the effect of spatially-correlated heterogeneity on isothermal drying of porous media. We combine a minimal pore-scale model with microfluidic experiments with the same pore geometry. Our simulated drying behavior compares favorably with experiments, considering the large sensitivity of the emergent behavior to the uncertainty associated with even small manufacturing errors. We show that increasing the correlation length in particle sizes promotes preferential drying of clusters of large pores, prolonging liquid connectivity and surface wetness and thus higher drying rates for longer periods. Our findings improve our quantitative understanding of how pore-scale heterogeneity impacts drying, which plays a role in a wide range of processes ranging from fuel cells to curing of paints and cements to global budgets of energy, water and solutes in soils.

Reply to 'Comments on upscaling geochemical reaction rates usingpore-scale network modeling' by Peter C. Lichtner and Qinjun Kang

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Li; Peters, Catherine A.; Celia, Michael A.

2006-05-03

Our paper "Upscaling geochemical reaction rates usingpore-scale network modeling" presents a novel application of pore-scalenetwork modeling to upscale mineral dissolution and precipitationreaction rates from the pore scale to the continuum scale, anddemonstrates the methodology by analyzing the scaling behavior ofanorthite and kaolinite reaction kinetics under conditions related to CO2sequestration. We conclude that under highly acidic conditions relevantto CO2 sequestration, the traditional continuum-based methodology may notcapture the spatial variation in concentrations from pore to pore, andscaling tools may be important in correctly modeling reactive transportprocesses in such systems. This work addresses the important butdifficult question of scaling mineral dissolution and precipitationreactionmore » kinetics, which is often ignored in fields such as geochemistry,water resources, and contaminant hydrology. Although scaling of physicalprocesses has been studied for almost three decades, very few studieshave examined the scaling issues related to chemical processes, despitetheir importance in governing the transport and fate of contaminants insubsurface systems.« less

Quantifying uncertainty and computational complexity for pore-scale simulations

NASA Astrophysics Data System (ADS)

Chen, C.; Yuan, Z.; Wang, P.; Yang, X.; Zhenyan, L.

2016-12-01

Pore-scale simulation is an essential tool to understand the complex physical process in many environmental problems, from multi-phase flow in the subsurface to fuel cells. However, in practice, factors such as sample heterogeneity, data sparsity and in general, our insufficient knowledge of the underlying process, render many simulation parameters and hence the prediction results uncertain. Meanwhile, most pore-scale simulations (in particular, direct numerical simulation) incur high computational cost due to finely-resolved spatio-temporal scales, which further limits our data/samples collection. To address those challenges, we propose a novel framework based on the general polynomial chaos (gPC) and build a surrogate model representing the essential features of the underlying system. To be specific, we apply the novel framework to analyze the uncertainties of the system behavior based on a series of pore-scale numerical experiments, such as flow and reactive transport in 2D heterogeneous porous media and 3D packed beds. Comparing with recent pore-scale uncertainty quantification studies using Monte Carlo techniques, our new framework requires fewer number of realizations and hence considerably reduce the overall computational cost, while maintaining the desired accuracy.

Pore scale study of multiphase multicomponent reactive transport during CO 2 dissolution trapping

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, Li; Wang, Mengyi; Kang, Qinjun

Solubility trapping is crucial for permanent CO 2 sequestration in deep saline aquifers. For the first time, a pore-scale numerical method is developed to investigate coupled scCO 2-water two-phase flow, multicomponent (CO 2(aq), H +, HCO 3 –, CO 3 2 – and OH –) mass transport, heterogeneous interfacial dissolution reaction, and homogeneous dissociation reactions. Pore-scale details of evolutions of multiphase distributions and concentration fields are presented and discussed. Time evolutions of several variables including averaged CO 2(aq) concentration, scCO 2 saturation, and pH value are analyzed. Specific interfacial length, an important variable which cannot be determined but is requiredmore » by continuum models, is investigated in detail. Mass transport coefficient or efficient dissolution rate is also evaluated. The pore-scale results show strong non-equilibrium characteristics during solubility trapping due to non-uniform distributions of multiphase as well as slow mass transport process. Complicated coupling mechanisms between multiphase flow, mass transport and chemical reactions are also revealed. Lastly, effects of wettability are also studied. The pore-scale studies provide deep understanding of non-linear non-equilibrium multiple physicochemical processes during CO 2 solubility trapping processes, and also allow to quantitatively predict some important empirical relationships, such as saturation-interfacial surface area, for continuum models.« less

Pore scale study of multiphase multicomponent reactive transport during CO 2 dissolution trapping

DOE PAGES

Chen, Li; Wang, Mengyi; Kang, Qinjun; ...

2018-04-26

Solubility trapping is crucial for permanent CO 2 sequestration in deep saline aquifers. For the first time, a pore-scale numerical method is developed to investigate coupled scCO 2-water two-phase flow, multicomponent (CO 2(aq), H +, HCO 3 –, CO 3 2 – and OH –) mass transport, heterogeneous interfacial dissolution reaction, and homogeneous dissociation reactions. Pore-scale details of evolutions of multiphase distributions and concentration fields are presented and discussed. Time evolutions of several variables including averaged CO 2(aq) concentration, scCO 2 saturation, and pH value are analyzed. Specific interfacial length, an important variable which cannot be determined but is requiredmore » by continuum models, is investigated in detail. Mass transport coefficient or efficient dissolution rate is also evaluated. The pore-scale results show strong non-equilibrium characteristics during solubility trapping due to non-uniform distributions of multiphase as well as slow mass transport process. Complicated coupling mechanisms between multiphase flow, mass transport and chemical reactions are also revealed. Lastly, effects of wettability are also studied. The pore-scale studies provide deep understanding of non-linear non-equilibrium multiple physicochemical processes during CO 2 solubility trapping processes, and also allow to quantitatively predict some important empirical relationships, such as saturation-interfacial surface area, for continuum models.« less

Pore scale study of multiphase multicomponent reactive transport during CO2 dissolution trapping

NASA Astrophysics Data System (ADS)

Chen, Li; Wang, Mengyi; Kang, Qinjun; Tao, Wenquan

2018-06-01

Solubility trapping is crucial for permanent CO2 sequestration in deep saline aquifers. For the first time, a pore-scale numerical method is developed to investigate coupled scCO2-water two-phase flow, multicomponent (CO2(aq), H+, HCO3-, CO32- and OH-) mass transport, heterogeneous interfacial dissolution reaction, and homogeneous dissociation reactions. Pore-scale details of evolutions of multiphase distributions and concentration fields are presented and discussed. Time evolutions of several variables including averaged CO2(aq) concentration, scCO2 saturation, and pH value are analyzed. Specific interfacial length, an important variable which cannot be determined but is required by continuum models, is investigated in detail. Mass transport coefficient or efficient dissolution rate is also evaluated. The pore-scale results show strong non-equilibrium characteristics during solubility trapping due to non-uniform distributions of multiphase as well as slow mass transport process. Complicated coupling mechanisms between multiphase flow, mass transport and chemical reactions are also revealed. Finally, effects of wettability are also studied. The pore-scale studies provide deep understanding of non-linear non-equilibrium multiple physicochemical processes during CO2 solubility trapping processes, and also allow to quantitatively predict some important empirical relationships, such as saturation-interfacial surface area, for continuum models.

A multiscale approach to accelerate pore-scale simulation of porous electrodes

NASA Astrophysics Data System (ADS)

Zheng, Weibo; Kim, Seung Hyun

2017-04-01

A new method to accelerate pore-scale simulation of porous electrodes is presented. The method combines the macroscopic approach with pore-scale simulation by decomposing a physical quantity into macroscopic and local variations. The multiscale method is applied to the potential equation in pore-scale simulation of a Proton Exchange Membrane Fuel Cell (PEMFC) catalyst layer, and validated with the conventional approach for pore-scale simulation. Results show that the multiscale scheme substantially reduces the computational cost without sacrificing accuracy.

Machine learning framework for analysis of transport through complex networks in porous, granular media: A focus on permeability

NASA Astrophysics Data System (ADS)

van der Linden, Joost H.; Narsilio, Guillermo A.; Tordesillas, Antoinette

2016-08-01

We present a data-driven framework to study the relationship between fluid flow at the macroscale and the internal pore structure, across the micro- and mesoscales, in porous, granular media. Sphere packings with varying particle size distribution and confining pressure are generated using the discrete element method. For each sample, a finite element analysis of the fluid flow is performed to compute the permeability. We construct a pore network and a particle contact network to quantify the connectivity of the pores and particles across the mesoscopic spatial scales. Machine learning techniques for feature selection are employed to identify sets of microstructural properties and multiscale complex network features that optimally characterize permeability. We find a linear correlation (in log-log scale) between permeability and the average closeness centrality of the weighted pore network. With the pore network links weighted by the local conductance, the average closeness centrality represents a multiscale measure of efficiency of flow through the pore network in terms of the mean geodesic distance (or shortest path) between all pore bodies in the pore network. Specifically, this study objectively quantifies a hypothesized link between high permeability and efficient shortest paths that thread through relatively large pore bodies connected to each other by high conductance pore throats, embodying connectivity and pore structure.

Estimating Pore Properties from NMR Relaxation Time Measurements in Heterogeneous Media

NASA Astrophysics Data System (ADS)

Grunewald, E.; Knight, R.

2008-12-01

The link between pore geometry and the nuclear magnetic resonance (NMR) relaxation time T2 is well- established for simple systems but is poorly understood for complex media with heterogeneous pores. Conventional interpretation of NMR relaxation data employs a model of isolated pores in which each hydrogen proton samples only one pore type, and the T2-distribution is directly scaled to estimate a pore-size distribution. During an actual NMR measurement, however, each proton diffuses through a finite volume of the pore network, and so may sample multiple pore types encountered within this diffusion cell. For cases in which heterogeneous pores are strongly coupled by diffusion, the meaning of the T2- distribution is not well understood and further research is required to determine how such measurements should be interpreted. In this study we directly investigate the implications of pore coupling in two groups of laboratory NMR experiments. We conduct two suites of experiments, in which samples are synthesized to exhibit a range of pore coupling strengths using two independent approaches: (a) varying the scale of the diffusion cell and (b) varying the scale over which heterogeneous pores are encountered. In the first set of experiments, we vary the scale of the diffusion cell in silica gels which have a bimodal pore-size distribution comprised of intragrannular micropores and much larger intergrannular pores. The untreated gel exhibits strong pore coupling with a single broad peak observed in the T2-distribution. By treating the gel with varied amounts of paramagnetic iron surface coatings, we decrease the surface relaxation time, T2S, and effectively decrease both the size of the diffusion cell and the degree of pore coupling. As more iron is coated to the grain surfaces, we observe a separation of the broad T2-distribution into two peaks that more accurately represent the true bimodal pore-size distribution. In the second set of experiments, we vary the scale over which heterogeneous pores are encountered in bimodal grain packs of pure quartz (long T2S) and hematite (short T2S). The scale of heterogeneity is varied by changing the mean grain size and relative mineral concentrations. When the mean grain size is small and the mineral concentrations are comparable, the T2-distribution is roughly monomodal indicating strong pore coupling. As the grain size is increased or the mineral concentrations are made increasingly uneven, the T2- distribution develops a bimodal character, more representative of the actual distribution of pore types. Numerical simulations of measurements in both experiment groups allow us to more closely investigate how the relaxing magnetization evolves in both time and space. Collectively, these experiments provide important insights into the effects of pore coupling on NMR measurements in heterogeneous systems and contribute to our ultimate goal of improving the interpretation of these data in complex near-surface sediments.

Water permeability in hydrate-bearing sediments: A pore-scale study

NASA Astrophysics Data System (ADS)

Dai, Sheng; Seol, Yongkoo

2014-06-01

Permeability is a critical parameter governing methane flux and fluid flow in hydrate-bearing sediments; however, limited valid data are available due to experimental challenges. Here we investigate the relationship between apparent water permeability (k') and hydrate saturation (Sh), accounting for hydrate pore-scale growth habit and meso-scale heterogeneity. Results from capillary tube models rely on cross-sectional tube shapes and hydrate pore habits, thus are appropriate only for sediments with uniform hydrate distribution and known hydrate pore character. Given our pore network modeling results showing that accumulating hydrate in sediments decreases sediment porosity and increases hydraulic tortuosity, we propose a modified Kozeny-Carman model to characterize water permeability in hydrate-bearing sediments. This model agrees well with experimental results and can be easily implemented in reservoir simulators with no empirical variables other than Sh. Results are also relevant to flow through other natural sediments that undergo diagenesis, salt precipitation, or bio-clogging.

Global sensitivity analysis of multiscale properties of porous materials

NASA Astrophysics Data System (ADS)

Um, Kimoon; Zhang, Xuan; Katsoulakis, Markos; Plechac, Petr; Tartakovsky, Daniel M.

2018-02-01

Ubiquitous uncertainty about pore geometry inevitably undermines the veracity of pore- and multi-scale simulations of transport phenomena in porous media. It raises two fundamental issues: sensitivity of effective material properties to pore-scale parameters and statistical parameterization of Darcy-scale models that accounts for pore-scale uncertainty. Homogenization-based maps of pore-scale parameters onto their Darcy-scale counterparts facilitate both sensitivity analysis (SA) and uncertainty quantification. We treat uncertain geometric characteristics of a hierarchical porous medium as random variables to conduct global SA and to derive probabilistic descriptors of effective diffusion coefficients and effective sorption rate. Our analysis is formulated in terms of solute transport diffusing through a fluid-filled pore space, while sorbing to the solid matrix. Yet it is sufficiently general to be applied to other multiscale porous media phenomena that are amenable to homogenization.

Pore-scale supercritical CO 2 dissolution and mass transfer under drainage conditions

DOE PAGES

Chang, Chun; Zhou, Quanlin; Oostrom, Mart; ...

2016-12-05

Recently, both core- and pore-scale imbibition experiments have shown non-equilibrium dissolution of supercritical CO 2 (scCO 2) and a prolonged depletion of residual scCO 2. In this paper, pore-scale scCO 2 dissolution and mass transfer under drainage conditions were investigated using a two-dimensional heterogeneous micromodel and a novel fluorescent water dye with a sensitive pH range between 3.7 and 6.5. Drainage experiments were conducted at 9 MPa and 40 °C by injecting scCO 2 into the sandstone-analogue pore network initially saturated by water without dissolved CO 2 (dsCO 2). During the experiments, time-lapse images of dye intensity, reflecting water pH,more » were obtained. These images show non-uniform pH in individual pores and pore clusters, with average pH levels gradually decreasing with time. Further analysis on selected pores and pore clusters shows that (1) rate-limited mass transfer prevails with slowly decreasing pH over time when the scCO 2-water interface area is low with respect to the volume of water-filled pores and pore clusters, (2) fast scCO 2 dissolution and phase equilibrium occurs when scCO 2 bubbles invade into water-filled pores, significantly enhancing the area-to-volume ratio, and (3) a transition from rate-limited to diffusion-limited mass transfer occurs in a single pore when a medium area-to-volume ratio is prevalent. The analysis also shows that two fundamental processes – scCO 2 dissolution at phase interfaces and diffusion of dsCO 2 at the pore scale (10–100 µm) observed after scCO 2 bubble invasion into water-filled pores without pore throat constraints – are relatively fast. The overall slow dissolution of scCO 2 in the millimeter-scale micromodel can be attributed to the small area-to-volume ratios that represent pore-throat configurations and characteristics of phase interfaces. Finally, this finding is applicable for the behavior of dissolution at pore, core, and field scales when water-filled pores and pore clusters of varying size are surrounded by scCO 2 at narrow pore throats.« less

Pore-scale supercritical CO 2 dissolution and mass transfer under drainage conditions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chang, Chun; Zhou, Quanlin; Oostrom, Mart

Recently, both core- and pore-scale imbibition experiments have shown non-equilibrium dissolution of supercritical CO 2 (scCO 2) and a prolonged depletion of residual scCO 2. In this paper, pore-scale scCO 2 dissolution and mass transfer under drainage conditions were investigated using a two-dimensional heterogeneous micromodel and a novel fluorescent water dye with a sensitive pH range between 3.7 and 6.5. Drainage experiments were conducted at 9 MPa and 40 °C by injecting scCO 2 into the sandstone-analogue pore network initially saturated by water without dissolved CO 2 (dsCO 2). During the experiments, time-lapse images of dye intensity, reflecting water pH,more » were obtained. These images show non-uniform pH in individual pores and pore clusters, with average pH levels gradually decreasing with time. Further analysis on selected pores and pore clusters shows that (1) rate-limited mass transfer prevails with slowly decreasing pH over time when the scCO 2-water interface area is low with respect to the volume of water-filled pores and pore clusters, (2) fast scCO 2 dissolution and phase equilibrium occurs when scCO 2 bubbles invade into water-filled pores, significantly enhancing the area-to-volume ratio, and (3) a transition from rate-limited to diffusion-limited mass transfer occurs in a single pore when a medium area-to-volume ratio is prevalent. The analysis also shows that two fundamental processes – scCO 2 dissolution at phase interfaces and diffusion of dsCO 2 at the pore scale (10–100 µm) observed after scCO 2 bubble invasion into water-filled pores without pore throat constraints – are relatively fast. The overall slow dissolution of scCO 2 in the millimeter-scale micromodel can be attributed to the small area-to-volume ratios that represent pore-throat configurations and characteristics of phase interfaces. Finally, this finding is applicable for the behavior of dissolution at pore, core, and field scales when water-filled pores and pore clusters of varying size are surrounded by scCO 2 at narrow pore throats.« less

Pore-scale investigation on the response of heterotrophic respiration to moisture conditions in heterogeneous soils

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yan, Zhifeng; Liu, Chongxuan; Todd-Brown, Katherine E.

The relationship between microbial respiration rate and soil moisture content is an important property for understanding and predicting soil organic carbon degradation, CO 2 production and emission, and their subsequent effects on climate change. This paper reports a pore-scale modeling study to investigate the response of heterotrophic respiration to moisture conditions in soils and to evaluate various factors that affect this response. X-ray computed tomography was used to derive soil pore structures, which were then used for pore-scale model investigation. The pore-scale results were then averaged to calculate the effective respiration rates as a function of water content in soils.more » The calculated effective respiration rate first increases and then decreases with increasing soil water content, showing a maximum respiration rate at water saturation degree of 0.75 that is consistent with field and laboratory observations. The relationship between the respiration rate and moisture content is affected by various factors, including pore-scale organic carbon bioavailability, the rate of oxygen delivery, soil pore structure and physical heterogeneity, soil clay content, and microbial drought resistivity. Simulations also illustrates that a larger fraction of CO 2 produced from microbial respiration can be accumulated inside soil cores under higher saturation conditions, implying that CO 2 flux measured on the top of soil cores may underestimate or overestimate true soil respiration rates under dynamic moisture conditions. Overall, this study provides mechanistic insights into the soil respiration response to the change in moisture conditions, and reveals a complex relationship between heterotrophic microbial respiration rate and moisture content in soils that is affected by various hydrological, geochemical, and biophysical factors.« less

Coupling lattice Boltzmann and continuum equations for flow and reactive transport in porous media.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Coon, Ethan; Porter, Mark L.; Kang, Qinjun

2012-06-18

In spatially and temporally localized instances, capturing sub-reservoir scale information is necessary. Capturing sub-reservoir scale information everywhere is neither necessary, nor computationally possible. The lattice Boltzmann Method for solving pore-scale systems. At the pore-scale, LBM provides an extremely scalable, efficient way of solving Navier-Stokes equations on complex geometries. Coupling pore-scale and continuum scale systems via domain decomposition. By leveraging the interpolations implied by pore-scale and continuum scale discretizations, overlapping Schwartz domain decomposition is used to ensure continuity of pressure and flux. This approach is demonstrated on a fractured medium, in which Navier-Stokes equations are solved within the fracture while Darcy'smore » equation is solved away from the fracture Coupling reactive transport to pore-scale flow simulators allows hybrid approaches to be extended to solve multi-scale reactive transport.« less

Condensation in Nanoporous Packed Beds.

PubMed

Ally, Javed; Molla, Shahnawaz; Mostowfi, Farshid

2016-05-10

In materials with tiny, nanometer-scale pores, liquid condensation is shifted from the bulk saturation pressure observed at larger scales. This effect is called capillary condensation and can block pores, which has major consequences in hydrocarbon production, as well as in fuel cells, catalysis, and powder adhesion. In this study, high pressure nanofluidic condensation studies are performed using propane and carbon dioxide in a colloidal crystal packed bed. Direct visualization allows the extent of condensation to be observed, as well as inference of the pore geometry from Bragg diffraction. We show experimentally that capillary condensation depends on pore geometry and wettability because these factors determine the shape of the menisci that coalesce when pore filling occurs, contrary to the typical assumption that all pore structures can be modeled as cylindrical and perfectly wetting. We also observe capillary condensation at higher pressures than has been done previously, which is important because many applications involving this phenomenon occur well above atmospheric pressure, and there is little, if any, experimental validation of capillary condensation at such pressures, particularly with direct visualization.

High-resolution face verification using pore-scale facial features.

PubMed

Li, Dong; Zhou, Huiling; Lam, Kin-Man

2015-08-01

Face recognition methods, which usually represent face images using holistic or local facial features, rely heavily on alignment. Their performances also suffer a severe degradation under variations in expressions or poses, especially when there is one gallery per subject only. With the easy access to high-resolution (HR) face images nowadays, some HR face databases have recently been developed. However, few studies have tackled the use of HR information for face recognition or verification. In this paper, we propose a pose-invariant face-verification method, which is robust to alignment errors, using the HR information based on pore-scale facial features. A new keypoint descriptor, namely, pore-Principal Component Analysis (PCA)-Scale Invariant Feature Transform (PPCASIFT)-adapted from PCA-SIFT-is devised for the extraction of a compact set of distinctive pore-scale facial features. Having matched the pore-scale features of two-face regions, an effective robust-fitting scheme is proposed for the face-verification task. Experiments show that, with one frontal-view gallery only per subject, our proposed method outperforms a number of standard verification methods, and can achieve excellent accuracy even the faces are under large variations in expression and pose.

Multiscale modeling of fluid flow and mass transport

NASA Astrophysics Data System (ADS)

Masuoka, K.; Yamamoto, H.; Bijeljic, B.; Lin, Q.; Blunt, M. J.

2017-12-01

In recent years, there are some reports on a simulation of fluid flow in pore spaces of rocks using Navier-Stokes equations. These studies mostly adopt a X-ray CT to create 3-D numerical grids of the pores in micro-scale. However, results may be of low accuracy when the rock has a large pore size distribution, because pores, whose size is smaller than resolution of the X-ray CT may be neglected. We recently found out by tracer tests in a laboratory using a brine saturated Ryukyu limestone and inject fresh water that a decrease of chloride concentration took longer time. This phenomenon can be explained due to weak connectivity of the porous networks. Therefore, it is important to simulate entire pore spaces even those of very small sizes in which diffusion is dominant. We have developed a new methodology for multi-level modeling for pore scale fluid flow in porous media. The approach is to combine pore-scale analysis with Darcy-flow analysis using two types of X-ray CT images in different resolutions. Results of the numerical simulations showed a close match with the experimental results. The proposed methodology is an enhancement for analyzing mass transport and flow phenomena in rocks with complicated pore structure.

Investigating the relative permeability behavior of microporosity-rich carbonates and tight sandstones with multiscale pore network models

NASA Astrophysics Data System (ADS)

Bultreys, Tom; Stappen, Jeroen Van; Kock, Tim De; Boever, Wesley De; Boone, Marijn A.; Hoorebeke, Luc Van; Cnudde, Veerle

2016-11-01

The relative permeability behavior of rocks with wide ranges of pore sizes is in many cases still poorly understood and is difficult to model at the pore scale. In this work, we investigate the capillary pressure and relative permeability behavior of three outcrop carbonates and two tight reservoir sandstones with wide, multimodal pore size distributions. To examine how the drainage and imbibition properties of these complex rock types are influenced by the connectivity of macropores to each other and to zones with unresolved small-scale porosity, we apply a previously presented microcomputed-tomography-based multiscale pore network model to these samples. The sensitivity to the properties of the small-scale porosity is studied by performing simulations with different artificial sphere-packing-based networks as a proxy for these pores. Finally, the mixed-wet water-flooding behavior of the samples is investigated, assuming different wettability distributions for the microporosity and macroporosity. While this work is not an attempt to perform predictive modeling, it seeks to qualitatively explain the behavior of the investigated samples and illustrates some of the most recent developments in multiscale pore network modeling.

New insights on the complex dynamics of two-phase flow in porous media under intermediate-wet conditions.

PubMed

Rabbani, Harris Sajjad; Joekar-Niasar, Vahid; Pak, Tannaz; Shokri, Nima

2017-07-04

Multiphase flow in porous media is important in a number of environmental and industrial applications such as soil remediation, CO 2 sequestration, and enhanced oil recovery. Wetting properties control flow of immiscible fluids in porous media and fluids distribution in the pore space. In contrast to the strong and weak wet conditions, pore-scale physics of immiscible displacement under intermediate-wet conditions is less understood. This study reports the results of a series of two-dimensional high-resolution direct numerical simulations with the aim of understanding the pore-scale dynamics of two-phase immiscible fluid flow under intermediate-wet conditions. Our results show that for intermediate-wet porous media, pore geometry has a strong influence on interface dynamics, leading to co-existence of concave and convex interfaces. Intermediate wettability leads to various interfacial movements which are not identified under imbibition or drainage conditions. These pore-scale events significantly influence macro-scale flow behaviour causing the counter-intuitive decline in recovery of the defending fluid from weak imbibition to intermediate-wet conditions.

Validation of model predictions of pore-scale fluid distributions during two-phase flow

NASA Astrophysics Data System (ADS)

Bultreys, Tom; Lin, Qingyang; Gao, Ying; Raeini, Ali Q.; AlRatrout, Ahmed; Bijeljic, Branko; Blunt, Martin J.

2018-05-01

Pore-scale two-phase flow modeling is an important technology to study a rock's relative permeability behavior. To investigate if these models are predictive, the calculated pore-scale fluid distributions which determine the relative permeability need to be validated. In this work, we introduce a methodology to quantitatively compare models to experimental fluid distributions in flow experiments visualized with microcomputed tomography. First, we analyzed five repeated drainage-imbibition experiments on a single sample. In these experiments, the exact fluid distributions were not fully repeatable on a pore-by-pore basis, while the global properties of the fluid distribution were. Then two fractional flow experiments were used to validate a quasistatic pore network model. The model correctly predicted the fluid present in more than 75% of pores and throats in drainage and imbibition. To quantify what this means for the relevant global properties of the fluid distribution, we compare the main flow paths and the connectivity across the different pore sizes in the modeled and experimental fluid distributions. These essential topology characteristics matched well for drainage simulations, but not for imbibition. This suggests that the pore-filling rules in the network model we used need to be improved to make reliable predictions of imbibition. The presented analysis illustrates the potential of our methodology to systematically and robustly test two-phase flow models to aid in model development and calibration.

Pore-Scale X-ray Micro-CT Imaging and Analysis of Oil Shales

NASA Astrophysics Data System (ADS)

Saif, T.

2015-12-01

The pore structure and the connectivity of the pore space during the pyrolysis of oil shales are important characteristics which determine hydrocarbon flow behaviour and ultimate recovery. We study the effect of temperature on the evolution of pore space and subsequent permeability on five oil shale samples: (1) Vernal Utah United States, (2) El Lajjun Al Karak Jordan, (3) Gladstone Queensland Australia (4) Fushun China and (5) Kimmerdige United Kingdom. Oil Shale cores of 5mm in diameter were pyrolized at 300, 400 and 500 °C. 3D imaging of 5mm diameter core samples was performed at 1μm voxel resolution using X-ray micro computed tomography (CT) and the evolution of the pore structures were characterized. The experimental results indicate that the thermal decomposition of kerogen at high temperatures is a major factor causing micro-scale changes in the internal structure of oil shales. At the early stage of pyrolysis, micron-scale heterogeneous pores were formed and with a further increase in temperature, the pores expanded and became interconnected by fractures. Permeability for each oil shale sample at each temperature was computed by simulation directly on the image voxels and by pore network extraction and simulation. Future work will investigate different samples and pursue insitu micro-CT imaging of oil shale pyrolysis to characterize the time evolution of the pore space.

Multi-scale characterization of pore evolution in a combustion metamorphic complex, Hatrurim basin, Israel: Combining (ultra) small-angle neutron scattering and image analysis

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Hsiu-Wen; Anovitz, Lawrence; Burg, Avihu

Backscattered scanning electron micrograph and ultra small- and small-angle neutron scattering data have been combined to provide statistically meaningful data on the pore/grain structure and pore evolution of combustion metamorphic complexes from the Hatrurim basin, Israel. Three processes, anti-sintering roughening, alteration of protolith (dehydration, decarbonation, and oxidation) and crystallization of high-temperature minerals, occurred simultaneously, leading to significant changes in observed pore/grain structures. Pore structures in the protoliths, and in lowand high-grade metamorphic rocks show surface (Ds) and mass (Dm) pore fractal geometries with gradual increases in both Ds and Dm values as a function of metamorphic grade. This suggests thatmore » increases in pore volume and formation of less branching pore networks are accompanied by a roughening of pore/grain interfaces. Additionally, pore evolution during combustion metamorphism is also characterized by reduced contributions from small-scale pores to the cumulative porosity in the high-grade rocks. At high temperatures, small-scale pores may be preferentially closed by the formation of high-temperature minerals, producing a rougher morphology with increasing temperature. Alternatively, large-scale pores may develop at the expense of small-scale pores. These observations (pore fractal geometry and cumulative porosity) indicate that the evolution of pore/grain structures is correlated with the growth of high-temperature phases and is a consequence of the energy balance between pore/grain surface energy and energy arising from heterogeneous phase contacts. The apparent pore volume density further suggests that the localized time/temperature development of the high-grade Hatrurim rocks is not simply an extension of that of the low-grade rocks. The former likely represents the "hot spots (burning foci)" in the overall metamorphic terrain while the latter may represent contact aureoles.« less

Quantitative high-resolution mapping of phenanthrene sorption to black carbon particles.

PubMed

Obst, Martin; Grathwohl, Peter; Kappler, Andreas; Eibl, Oliver; Peranio, Nicola; Gocht, Tilman

2011-09-01

Sorption of hydrophobic organic contaminants such as polycyclic aromatic hydrocarbons (PAHs) to black carbon (BC) particles has been the focus of numerous studies. Conclusions on sorption mechanisms of PAH on BC were mostly derived from studies of sorption isotherms and sorption kinetics, which are based on batch experiments. However, mechanistic modeling approaches consider processes at the subparticle scale, some including transport within the pore-space or different spatial pore-domains. Direct evidence based on analytical techniques operating at the submicrometer scale for the location of sorption sites and the adsorbed species is lacking. In this work, we identified, quantified, and mapped the sorption of PAHs on different BC particles (activated carbon, charcoal and diesel soot) on a 25-100 nm scale using scanning transmission X-ray microscopy (STXM). In addition, we visualized the pore structure of the particles by transmission electron microscopy (TEM) on the 1-10 nm-scale. The combination of the chemical information from STXM with the physical information from TEM revealed that phenanthrene accumulates in the interconnected pore-system along primary "cracks" in the particles, confirming an adsorption mechanism.

Determination of pore-scale hydrate phase equilibria in sediments using lab-on-a-chip technology.

PubMed

Almenningen, Stian; Flatlandsmo, Josef; Kovscek, Anthony R; Ersland, Geir; Fernø, Martin A

2017-11-21

We present an experimental protocol for fast determination of hydrate stability in porous media for a range of pressure and temperature (P, T) conditions. Using a lab-on-a-chip approach, we gain direct optical access to dynamic pore-scale hydrate formation and dissociation events to study the hydrate phase equilibria in sediments. Optical pore-scale observations of phase behavior reproduce the theoretical hydrate stability line with methane gas and distilled water, and demonstrate the accuracy of the new method. The procedure is applicable for any kind of hydrate transitions in sediments, and may be used to map gas hydrate stability zones in nature.

An Image-based Micro-continuum Pore-scale Model for Gas Transport in Organic-rich Shale

NASA Astrophysics Data System (ADS)

Guo, B.; Tchelepi, H.

2017-12-01

Gas production from unconventional source rocks, such as ultra-tight shales, has increased significantly over the past decade. However, due to the extremely small pores ( 1-100 nm) and the strong material heterogeneity, gas flow in shale is still not well understood and poses challenges for predictive field-scale simulations. In recent years, digital rock analysis has been applied to understand shale gas transport at the pore-scale. An issue with rock images (e.g. FIB-SEM, nano-/micro-CT images) is the so-called "cutoff length", i.e., pores and heterogeneities below the resolution cannot be resolved, which leads to two length scales (resolved features and unresolved sub-resolution features) that are challenging for flow simulations. Here we develop a micro-continuum model, modified from the classic Darcy-Brinkman-Stokes framework, that can naturally couple the resolved pores and the unresolved nano-porous regions. In the resolved pores, gas flow is modeled with Stokes equation. In the unresolved regions where the pore sizes are below the image resolution, we develop an apparent permeability model considering non-Darcy flow at the nanoscale including slip flow, Knudsen diffusion, adsorption/desorption, surface diffusion, and real gas effect. The end result is a micro-continuum pore-scale model that can simulate gas transport in 3D reconstructed shale images. The model has been implemented in the open-source simulation platform OpenFOAM. In this paper, we present case studies to demonstrate the applicability of the model, where we use 3D segmented FIB-SEM and nano-CT shale images that include four material constituents: organic matter, clay, granular mineral, and pore. In addition to the pore structure and the distribution of the material constituents, we populate the model with experimental measurements (e.g. size distribution of the sub-resolution pores from nitrogen adsorption) and parameters from the literature and identify the relative importance of different physics on gas production. Overall, the micro-continuum model provides a novel tool for digital rock analysis of organic-rich shale.

An investigation into preserving spatially-distinct pore systems in multi-component rocks using a fossiliferous limestone example

NASA Astrophysics Data System (ADS)

Jiang, Zeyun; Couples, Gary D.; Lewis, Helen; Mangione, Alessandro

2018-07-01

Limestones containing abundant disc-shaped fossil Nummulites can form significant hydrocarbon reservoirs but they have a distinctly heterogeneous distribution of pore shapes, sizes and connectivities, which make it particularly difficult to calculate petrophysical properties and consequent flow outcomes. The severity of the problem rests on the wide length-scale range from the millimetre scale of the fossil's pore space to the micron scale of rock matrix pores. This work develops a technique to incorporate multi-scale void systems into a pore network, which is used to calculate the petrophysical properties for subsequent flow simulations at different stages in the limestone's petrophysical evolution. While rock pore size, shape and connectivity can be determined, with varying levels of fidelity, using techniques such as X-ray computed tomography (CT) or scanning electron microscopy (SEM), this work represents a more challenging class where the rock of interest is insufficiently sampled or, as here, has been overprinted by extensive chemical diagenesis. The main challenge is integrating multi-scale void structures derived from both SEM and CT images, into a single model or a pore-scale network while still honouring the nature of the connections across these length scales. Pore network flow simulations are used to illustrate the technique but of equal importance, to demonstrate how supportable earlier-stage petrophysical property distributions can be used to assess the viability of several potential geological event sequences. The results of our flow simulations on generated models highlight the requirement for correct determination of the dominant pore scales (one plus of nm, μm, mm, cm), the spatial correlation and the cross-scale connections.

Pore-Scale Simulation and Sensitivity Analysis of Apparent Gas Permeability in Shale Matrix

PubMed Central

Zhang, Pengwei; Hu, Liming; Meegoda, Jay N.

2017-01-01

Extremely low permeability due to nano-scale pores is a distinctive feature of gas transport in a shale matrix. The permeability of shale depends on pore pressure, porosity, pore throat size and gas type. The pore network model is a practical way to explain the macro flow behavior of porous media from a microscopic point of view. In this research, gas flow in a shale matrix is simulated using a previously developed three-dimensional pore network model that includes typical bimodal pore size distribution, anisotropy and low connectivity of the pore structure in shale. The apparent gas permeability of shale matrix was calculated under different reservoir pressures corresponding to different gas exploitation stages. Results indicate that gas permeability is strongly related to reservoir gas pressure, and hence the apparent permeability is not a unique value during the shale gas exploitation, and simulations suggested that a constant permeability for continuum-scale simulation is not accurate. Hence, the reservoir pressures of different shale gas exploitations should be considered. In addition, a sensitivity analysis was also performed to determine the contributions to apparent permeability of a shale matrix from petro-physical properties of shale such as pore throat size and porosity. Finally, the impact of connectivity of nano-scale pores on shale gas flux was analyzed. These results would provide an insight into understanding nano/micro scale flows of shale gas in the shale matrix. PMID:28772465

Pore-Scale Simulation and Sensitivity Analysis of Apparent Gas Permeability in Shale Matrix.

PubMed

Zhang, Pengwei; Hu, Liming; Meegoda, Jay N

2017-01-25

Extremely low permeability due to nano-scale pores is a distinctive feature of gas transport in a shale matrix. The permeability of shale depends on pore pressure, porosity, pore throat size and gas type. The pore network model is a practical way to explain the macro flow behavior of porous media from a microscopic point of view. In this research, gas flow in a shale matrix is simulated using a previously developed three-dimensional pore network model that includes typical bimodal pore size distribution, anisotropy and low connectivity of the pore structure in shale. The apparent gas permeability of shale matrix was calculated under different reservoir pressures corresponding to different gas exploitation stages. Results indicate that gas permeability is strongly related to reservoir gas pressure, and hence the apparent permeability is not a unique value during the shale gas exploitation, and simulations suggested that a constant permeability for continuum-scale simulation is not accurate. Hence, the reservoir pressures of different shale gas exploitations should be considered. In addition, a sensitivity analysis was also performed to determine the contributions to apparent permeability of a shale matrix from petro-physical properties of shale such as pore throat size and porosity. Finally, the impact of connectivity of nano-scale pores on shale gas flux was analyzed. These results would provide an insight into understanding nano/micro scale flows of shale gas in the shale matrix.

Numerical simulation on hydromechanical coupling in porous media adopting three-dimensional pore-scale model.

PubMed

Liu, Jianjun; Song, Rui; Cui, Mengmeng

2014-01-01

A novel approach of simulating hydromechanical coupling in pore-scale models of porous media is presented in this paper. Parameters of the sandstone samples, such as the stress-strain curve, Poisson's ratio, and permeability under different pore pressure and confining pressure, are tested in laboratory scale. The micro-CT scanner is employed to scan the samples for three-dimensional images, as input to construct the model. Accordingly, four physical models possessing the same pore and rock matrix characteristics as the natural sandstones are developed. Based on the micro-CT images, the three-dimensional finite element models of both rock matrix and pore space are established by MIMICS and ICEM software platform. Navier-Stokes equation and elastic constitutive equation are used as the mathematical model for simulation. A hydromechanical coupling analysis in pore-scale finite element model of porous media is simulated by ANSYS and CFX software. Hereby, permeability of sandstone samples under different pore pressure and confining pressure has been predicted. The simulation results agree well with the benchmark data. Through reproducing its stress state underground, the prediction accuracy of the porous rock permeability in pore-scale simulation is promoted. Consequently, the effects of pore pressure and confining pressure on permeability are revealed from the microscopic view.

Numerical Simulation on Hydromechanical Coupling in Porous Media Adopting Three-Dimensional Pore-Scale Model

PubMed Central

Liu, Jianjun; Song, Rui; Cui, Mengmeng

2014-01-01

A novel approach of simulating hydromechanical coupling in pore-scale models of porous media is presented in this paper. Parameters of the sandstone samples, such as the stress-strain curve, Poisson's ratio, and permeability under different pore pressure and confining pressure, are tested in laboratory scale. The micro-CT scanner is employed to scan the samples for three-dimensional images, as input to construct the model. Accordingly, four physical models possessing the same pore and rock matrix characteristics as the natural sandstones are developed. Based on the micro-CT images, the three-dimensional finite element models of both rock matrix and pore space are established by MIMICS and ICEM software platform. Navier-Stokes equation and elastic constitutive equation are used as the mathematical model for simulation. A hydromechanical coupling analysis in pore-scale finite element model of porous media is simulated by ANSYS and CFX software. Hereby, permeability of sandstone samples under different pore pressure and confining pressure has been predicted. The simulation results agree well with the benchmark data. Through reproducing its stress state underground, the prediction accuracy of the porous rock permeability in pore-scale simulation is promoted. Consequently, the effects of pore pressure and confining pressure on permeability are revealed from the microscopic view. PMID:24955384

Effective pore-scale dispersion upscaling with a correlated continuous time random walk approach

NASA Astrophysics Data System (ADS)

Le Borgne, T.; Bolster, D.; Dentz, M.; de Anna, P.; Tartakovsky, A.

2011-12-01

We investigate the upscaling of dispersion from a pore-scale analysis of Lagrangian velocities. A key challenge in the upscaling procedure is to relate the temporal evolution of spreading to the pore-scale velocity field properties. We test the hypothesis that one can represent Lagrangian velocities at the pore scale as a Markov process in space. The resulting effective transport model is a continuous time random walk (CTRW) characterized by a correlated random time increment, here denoted as correlated CTRW. We consider a simplified sinusoidal wavy channel model as well as a more complex heterogeneous pore space. For both systems, the predictions of the correlated CTRW model, with parameters defined from the velocity field properties (both distribution and correlation), are found to be in good agreement with results from direct pore-scale simulations over preasymptotic and asymptotic times. In this framework, the nontrivial dependence of dispersion on the pore boundary fluctuations is shown to be related to the competition between distribution and correlation effects. In particular, explicit inclusion of spatial velocity correlation in the effective CTRW model is found to be important to represent incomplete mixing in the pore throats.

High Fidelity Computational Analysis of CO2 Trapping at Pore Scales

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kumar, Vinod

2013-07-13

With an alarming rise in carbon dioxide (CO2) emission from anthropogenic sources, CO2 sequestration has become an attractive choice to mitigate the emission. Some popular storage media for CO{sub 2} are oil reservoirs, deep coal-bed, and deep oceanic-beds. These have been used for the long term CO{sub 2} storage. Due to special lowering viscosity and surface tension property of CO{sub 2}, it has been widely used for enhanced oil recovery. The sites for CO{sub 2} sequestration or enhanced oil recovery mostly consist of porous rocks. Lack of knowledge of molecular mobility under confinement and molecule-surface interactions between CO2 and naturalmore » porous media results in generally governed by unpredictable absorption kinetics and total absorption capacity for injected fluids, and therefore, constitutes barriers to the deployment of this technology. Therefore, it is important to understand the flow dynamics of CO{sub 2} through the porous microstructures at the finest scale (pore-scale) to accurately predict the storage potential and long-term dynamics of the sequestered CO{sub 2}. This report discusses about pore-network flow modeling approach using variational method and analyzes simulated results this method simulations at pore-scales for idealized network and using Berea Sandstone CT scanned images. Variational method provides a promising way to study the kinetic behavior and storage potential at the pore scale in the presence of other phases. The current study validates variational solutions for single and two-phase Newtonian and single phase non-Newtonian flow through angular pores for special geometries whose analytical and/or empirical solutions are known. The hydraulic conductance for single phase flow through a triangular duct was also validated against empirical results derived from lubricant theory.« less

A New Dual-Pore Formation Factor Model: A Percolation Network Study and Comparison to Experimental Data

NASA Astrophysics Data System (ADS)

Tang, Y. B.; Li, M.; Bernabe, Y.

2014-12-01

We modeled the electrical transport behavior of dual-pore carbonate rocks in this paper. Based on experimental data of a carbonate reservoir in China, we simply considered the low porosity samples equivalent to the matrix (micro-pore system) of the high porosity samples. For modeling the bimodal porous media, we considered that the matrix is homogeneous and interconnected. The connectivity and the pore size distribution of macro-pore system are varied randomly. Both pore systems are supposed to act electrically in parallel, connected at the nodes, where the fluid exchange takes place, an approach previously used by Bauer et al. (2012). Then, the effect of the properties of matrix, the pore size distribution and connectivity of macro-pore system on petrophysical properties of carbonates can be investigated. We simulated electrical current through networks in three-dimensional simple cubic (SC) and body-center cubic (BCC) with different coordination numbers and different pipe radius distributions of macro-pore system. Based on the simulation results, we found that the formation factor obeys a "universal" scaling relationship (i.e. independent of lattice type), 1/F∝eγz, where γ is a function of the normalized standard deviation of the pore radius distribution of macro-pore system and z is the coordination number of macro-pore system. This relationship is different from the classic "universal power law" in percolation theory. A formation factor model was inferred on the basis of the scaling relationship mentioned above and several scale-invariant quantities (such as hydraulic radius rH and throat length l of macro-pore). Several methods were developed to estimate corresponding parameters of the new model with conventional core analyses. It was satisfactorily tested against experimental data, including some published experimental data. Furthermore, the relationship between water saturation and resistivity in dual-pore carbonates was discussed based on the new model.

Frequency Dependent Macro-dispersion Induced by Oscillatory Inputs and Spatial Heterogeneity

NASA Astrophysics Data System (ADS)

Rajabi, F.; Battiato, I.

2017-12-01

Elucidating flow and transport processes at the pore scale is the cornerstone of most hydrologic studies in the subsurface. This becomes even more imperative when the system is subject to a cyclic forcing. Such temporal variations with evolving heterogeneity of time scales spanning from days to years can influence transport phenomena at the pore level, e.g. yearly freeze/thaw in the thin active layer of soil above permafrost zone whose thickness increases throughout the thaw season. Moreover, understanding the interactions of different physical phenomena at the pore scale is key to predict the behavior at the continuum scale. Yet, the connection between periodic inputs at the pore scale and macrotransport is to a great extent unknown. In the spirit of homogenization technique, we derived a macrotime continuum-scale equation as well as expressions for the effective transport coefficients. The macrodispersion arises from contributions of molecular diffusion, spatial heterogeneity and time-dependent fluctuations. Moreover, we have quantified the solute spreading by effective dispersion in terms of dimensionless numbers (Pe, Da, and Strouhal), i.e. expressing the interplay of molecular diffusion, advection, reaction and signal frequency. Yet, as every macroscopic model, spatiotemporally averaged models can breakdown when certain criteria are violated. This makes the continuum scale equation a poor approximation for the processes at the pore scale. To this end, we also provide the conditions under which the space-time averaged equations accurately describe pore-scale processes. In addition, this study gives a robust evidence that transverse mixing can in fact benefit from fluctuating boundary forcing due to the interaction of temporal fluctuations and molecular diffusion. Furthermore, it provides a robust quantitative foundation for designing the desired systems since the interplay of geometry and external forcing has been directly connected to each other in terms of dimensionless (St) number. We compare our theoretical framework with data from an experiment performed on several micro-channels with different geometry and different frequencies of injection at the inlet. The proposed formulation is found to provide remarkably good predictions and correctly explain the experimental mixing dynamics.

Multi-scale modeling of multi-component reactive transport in geothermal aquifers

NASA Astrophysics Data System (ADS)

Nick, Hamidreza M.; Raoof, Amir; Wolf, Karl-Heinz; Bruhn, David

2014-05-01

In deep geothermal systems heat and chemical stresses can cause physical alterations, which may have a significant effect on flow and reaction rates. As a consequence it will lead to changes in permeability and porosity of the formations due to mineral precipitation and dissolution. Large-scale modeling of reactive transport in such systems is still challenging. A large area of uncertainty is the way in which the pore-scale information controlling the flow and reaction will behave at a larger scale. A possible choice is to use constitutive relationships relating, for example the permeability and porosity evolutions to the change in the pore geometry. While determining such relationships through laboratory experiments may be limited, pore-network modeling provides an alternative solution. In this work, we introduce a new workflow in which a hybrid Finite-Element Finite-Volume method [1,2] and a pore network modeling approach [3] are employed. Using the pore-scale model, relevant constitutive relations are developed. These relations are then embedded in the continuum-scale model. This approach enables us to study non-isothermal reactive transport in porous media while accounting for micro-scale features under realistic conditions. The performance and applicability of the proposed model is explored for different flow and reaction regimes. References: 1. Matthäi, S.K., et al.: Simulation of solute transport through fractured rock: a higher-order accurate finite-element finite-volume method permitting large time steps. Transport in porous media 83.2 (2010): 289-318. 2. Nick, H.M., et al.: Reactive dispersive contaminant transport in coastal aquifers: Numerical simulation of a reactive Henry problem. Journal of contaminant hydrology 145 (2012), 90-104. 3. Raoof A., et al.: PoreFlow: A Complex pore-network model for simulation of reactive transport in variably saturated porous media, Computers & Geosciences, 61, (2013), 160-174.

Quantitative analysis of nano-pore geomaterials and representative sampling for digital rock physics

NASA Astrophysics Data System (ADS)

Yoon, H.; Dewers, T. A.

2014-12-01

Geomaterials containing nano-pores (e.g., shales and carbonate rocks) have become increasingly important for emerging problems such as unconventional gas and oil resources, enhanced oil recovery, and geologic storage of CO2. Accurate prediction of coupled geophysical and chemical processes at the pore scale requires realistic representation of pore structure and topology. This is especially true for chalk materials, where pore networks are small and complex, and require characterization at sub-micron scale. In this work, we apply laser scanning confocal microscopy to characterize pore structures and microlithofacies at micron- and greater scales and dual focused ion beam-scanning electron microscopy (FIB-SEM) for 3D imaging of nanometer-to-micron scale microcracks and pore distributions. With imaging techniques advanced for nano-pore characterization, a problem of scale with FIB-SEM images is how to take nanometer scale information and apply it to the thin-section or larger scale. In this work, several texture characterization techniques including graph-based spectral segmentation, support vector machine, and principal component analysis are applied for segmentation clusters represented by 1-2 FIB-SEM samples per each cluster. Geometric and topological properties are analyzed and lattice-Boltzmann method (LBM) is used to obtain permeability at several different scales. Upscaling of permeability to the Darcy scale (e.g., the thin-section scale) with image dataset will be discussed with emphasis on understanding microfracture-matrix interaction, representative volume for FIB-SEM sampling, and multiphase flow and reactive transport. Funding from the DOE Basic Energy Sciences Geosciences Program is gratefully acknowledged. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

Physical Explanation of Archie's Porosity Exponent in Granular Materials: A Process-Based, Pore-Scale Numerical Study

NASA Astrophysics Data System (ADS)

Niu, Qifei; Zhang, Chi

2018-02-01

The empirical Archie's law has been widely used in geosciences and engineering to explain the measured electrical resistivity of many geological materials, but its physical basis has not been fully understood yet. In this study, we use a pore-scale numerical approach combining discrete element-finite difference methods to study Archie's porosity exponent m of granular materials over a wide porosity range. Numerical results reveal that at dilute states (e.g., porosity ϕ > 65%), m is exclusively related to the particle shape and orientation. As the porosity decreases, the electric flow in pore space concentrates progressively near particle contacts and m increases continuously in response to the intensified nonuniformity of the local electrical field. It is also found that the increase in m is universally correlated with the volume fraction of pore throats for all the samples regardless of their particle shapes, particle size range, and porosities.

From Pore to Core: Do Engineered Nanoparticles Violate Upscaling Assumptions? A Microtomographic Investigation

NASA Astrophysics Data System (ADS)

Molnar, I. L.; O'Carroll, D. M.; Gerhard, J.; Willson, C. S.

2014-12-01

The recent success in using Synchrotron X-ray Computed Microtomography (SXCMT) for the quantification of nanoparticle concentrations within real, three-dimensional pore networks [1] has opened up new opportunities for collecting experimental data of pore-scale flow and transport processes. One opportunity is coupling SXCMT with nanoparticle/soil transport experiments to provide unique insights into how pore-scale processes influence transport at larger scales. Understanding these processes is a key step in accurately upscaling micron-scale phenomena to the continuum-scale. Upscaling phenomena from the micron-scale to the continuum-scale typically involves the assumption that the pore space is well mixed. Using this 'well mixed assumption' it is implicitly assumed that the distribution of nanoparticles within the pore does not affect its retention by soil grains. This assumption enables the use of volume-averaged parameters in calculating transport and retention rates. However, in some scenarios, the well mixed assumption will likely be violated by processes such as deposition and diffusion. These processes can alter the distribution of the nanoparticles in the pore space and impact retention behaviour, leading to discrepancies between theoretical predictions and experimental observations. This work investigates the well mixed assumption by employing SXCMT to experimentally examine pore-scale mixing of silver nanoparticles during transport through sand packed columns. Silver nanoparticles were flushed through three different sands to examine the impact of grain distribution and nanoparticle retention rates on mixing: uniform silica (low retention), well graded silica sand (low retention) and uniform iron oxide coated silica sand (high retention). The SXCMT data identified diffusion-limited retention as responsible for violations of the well mixed assumption. A mathematical description of the diffusion-limited retention process was created and compared to the experimental data at the pore and column-scale. The mathematical description accurately predicted trends observed within the SXCMT-datasets such as concentration gradients away from grain surfaces and also accurately predicted total retention of nanoparticles at the column scale. 1. ES&T 2014, 48, (2), 1114-1122.

Non-scaling behavior of electroosmotic flow in voltage-gated nanopores

DOE PAGES

Lian, Cheng; Gallegos, Alejandro; Liu, Honglai; ...

2016-11-17

Ionic transport through nanopores is of fundamental importance for the design and development of nanofiltration membranes and novel electrochemical devices including supercapacitors, fuel cells and batteries. Recent experiments have shown an unusual variation of electrical conductance with the pore size and the electrolyte parameters that defies conventional scaling relations. Here ionic transport through voltage-gated nanopores was studied by using the classical density functional theory for ion distributions in combination with the Navier–Stokes equation for the electroosmotic flow. We also identified a significant influence of the gating potential on the scaling behavior of the conductance with changes in the pore sizemore » and the salt concentration. Finally, for ion transport in narrow pores with a high gating voltage, the conductivity shows an oscillatory dependence on the pore size owing to the strong overlap of electric double layers.« less

Direct pore-scale reactive transport modelling of dynamic wettability changes induced by surface complexation

NASA Astrophysics Data System (ADS)

Maes, Julien; Geiger, Sebastian

2018-01-01

Laboratory experiments have shown that oil production from sandstone and carbonate reservoirs by waterflooding could be significantly increased by manipulating the composition of the injected water (e.g. by lowering the ionic strength). Recent studies suggest that a change of wettability induced by a change in surface charge is likely to be one of the driving mechanism of the so-called low-salinity effect. In this case, the potential increase of oil recovery during waterflooding at low ionic strength would be strongly impacted by the inter-relations between flow, transport and chemical reaction at the pore-scale. Hence, a new numerical model that includes two-phase flow, solute reactive transport and wettability alteration is implemented based on the Direct Numerical Simulation of the Navier-Stokes equations and surface complexation modelling. Our model is first used to match experimental results of oil droplet detachment from clay patches. We then study the effect of wettability change on the pore-scale displacement for simple 2D calcite micro-models and evaluate the impact of several parameters such as water composition and injected velocity. Finally, we repeat the simulation experiments on a larger and more complex pore geometry representing a carbonate rock. Our simulations highlight two different effects of low-salinity on oil production from carbonate rocks: a smaller number of oil clusters left in the pores after invasion, and a greater number of pores invaded.

Polarity control at interfaces: Quantifying pseudo-solvent effects in nano-confined systems

DOE PAGES

Singappuli-Arachchige, Dilini; Manzano, J. Sebastian; Sherman, Lindy M.; ...

2016-08-02

Surface functionalization controls local environments and induces solvent-like effects at liquid–solid interfaces. We explored structure–property relationships between organic groups bound to pore surfaces of mesoporous silica nanoparticles and Stokes shifts of the adsorbed solvatochromic dye Prodan. Correlating shifts of the dye on the surfaces with its shifts in solvents resulted in a local polarity scale for functionalized pores. The scale was validated by studying the effects of pore polarity on quenching of Nile Red fluorescence and on the vibronic band structure of pyrene. Measurements were done in aqueous suspensions of porous particles, proving that the dielectric properties in the poresmore » are different from the bulk solvent. The precise control of pore polarity was used to enhance the catalytic activity of TEMPO in the aerobic oxidation of furfuryl alcohol in water. Furthermore, an inverse relationship was found between pore polarity and activity of TEMPO in the pores, demonstrating that controlling the local polarity around an active site allows modulating the activity of nanoconfined catalysts.« less

Characterization of Mixed Wettability at Different Scales and its Impact on Oil Recovery Efficiency

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sharma, Mukul M.; Hirasaki, George J.

The objectives of this project was to: (1) quantify the pore scale mechanisms that determine the wettability state of a reservoir, (2) study the effect of crude oil, brine and mineral compositions in the establishment of mixed wet states, (3) clarify the effect of mixed - wettability on oil displacement efficiency in waterfloods, (4) develop a new tracer technique to measure wettability, fluid distributions, residual saturation's and relative permeabilities, and (5) develop methods for properly incorporating wettability in up-scaling from pore to core to reservoir scales.

Visualization and prediction of supercritical CO 2 distribution in sandstones during drainage: An in situ synchrotron X-ray micro-computed tomography study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Voltolini, Marco; Kwon, Tae-Hyuk; Ajo-Franklin, Jonathan

Pore-scale distribution of supercritical CO 2 (scCO 2) exerts significant control on a variety of key hydrologic as well as geochemical processes, including residual trapping and dissolution. Despite such importance, only a small number of experiments have directly characterized the three-dimensional distribution of scCO 2 in geologic materials during the invasion (drainage) process. Here, we present a study which couples dynamic high-resolution synchrotron X-ray micro-computed tomography imaging of a scCO 2/brine system at in situ pressure/temperature conditions with quantitative pore-scale modeling to allow direct validation of a pore-scale description of scCO2 distribution. The experiment combines high-speed synchrotron radiography with tomographymore » to characterize the brine saturated sample, the scCO 2 breakthrough process, and the partially saturated state of a sandstone sample from the Domengine Formation, a regionally extensive unit within the Sacramento Basin (California, USA). The availability of a 3D dataset allowed us to examine correlations between grains and pores morphometric parameters and the actual distribution of scCO 2 in the sample, including the examination of the role of small-scale sedimentary structure on CO2 distribution. The segmented scCO 2/brine volume was also used to validate a simple computational model based on the local thickness concept, able to accurately simulate the distribution of scCO 2 after drainage. The same method was also used to simulate Hg capillary pressure curves with satisfactory results when compared to the measured ones. Finally, this predictive approach, requiring only a tomographic scan of the dry sample, proved to be an effective route for studying processes related to CO 2 invasion structure in geological samples at the pore scale.« less

Visualization and prediction of supercritical CO 2 distribution in sandstones during drainage: An in situ synchrotron X-ray micro-computed tomography study

DOE PAGES

Voltolini, Marco; Kwon, Tae-Hyuk; Ajo-Franklin, Jonathan

2017-10-21

Pore-scale distribution of supercritical CO 2 (scCO 2) exerts significant control on a variety of key hydrologic as well as geochemical processes, including residual trapping and dissolution. Despite such importance, only a small number of experiments have directly characterized the three-dimensional distribution of scCO 2 in geologic materials during the invasion (drainage) process. Here, we present a study which couples dynamic high-resolution synchrotron X-ray micro-computed tomography imaging of a scCO 2/brine system at in situ pressure/temperature conditions with quantitative pore-scale modeling to allow direct validation of a pore-scale description of scCO2 distribution. The experiment combines high-speed synchrotron radiography with tomographymore » to characterize the brine saturated sample, the scCO 2 breakthrough process, and the partially saturated state of a sandstone sample from the Domengine Formation, a regionally extensive unit within the Sacramento Basin (California, USA). The availability of a 3D dataset allowed us to examine correlations between grains and pores morphometric parameters and the actual distribution of scCO 2 in the sample, including the examination of the role of small-scale sedimentary structure on CO2 distribution. The segmented scCO 2/brine volume was also used to validate a simple computational model based on the local thickness concept, able to accurately simulate the distribution of scCO 2 after drainage. The same method was also used to simulate Hg capillary pressure curves with satisfactory results when compared to the measured ones. Finally, this predictive approach, requiring only a tomographic scan of the dry sample, proved to be an effective route for studying processes related to CO 2 invasion structure in geological samples at the pore scale.« less

The effect of pore-scale geometry and wettability on two-phase relative permeabilities within elementary cells

NASA Astrophysics Data System (ADS)

Bianchi Janetti, Emanuela; Riva, Monica; Guadagnini, Alberto

2017-04-01

We study the relative role of the complex pore space geometry and wettability of the solid matrix on the quantification of relative permeabilities characterizing steady state immiscible two-phase flow in porous media. We do so by considering elementary cells, which are typically employed in upscaling frameworks based on, e.g., homogenization or volume averaging. In this context one typically relies on the solution of pore-scale physics at a scale which is much smaller than that of an investigated porous system. Pressure-driven two-phase flow following simultaneous co-current injection of water and oil is numerically solved for a suite of regular and stochastically generated two-dimensional explicit elementary cells with fixed porosity and sharing main topological/morphological features. We show that relative permeabilities of the randomly generated elementary cells are significantly influenced by the formation of preferential percolation paths (principal pathways), giving rise to a strongly nonuniform distribution of fluid fluxes. These pathways are a result of the spatially variable resistance that the random pore structures exert on the fluid. The overall effect on relative permeabilities of the diverse organization of principal pathways, as driven by a given random realization at the scale of the unit cell, is significantly larger than that of the wettability of the host rock. In contrast to what can be observed for the random cells analyzed, relative permeabilities of regular cells display a clear trend with contact angle at the investigated scale. Our findings suggest the need to perform systematic upscaling studies in a stochastic context, to propagate the effects of uncertain pore space geometries to a probabilistic description of relative permeability curves at the continuum scale.

Pore-scale simulation of wettability and interfacial tension effects on flooding process for enhanced oil recovery.

PubMed

Zhao, Jin; Wen, Dongsheng

2017-08-27

For enhanced oil recovery (EOR) applications, the oil/water flow characteristics during the flooding process was numerically investigated with the volume-of-fluid method at the pore scale. A two-dimensional pore throat-body connecting structure was established, and four scenarios were simulated in this paper. For oil-saturated pores, the wettability effect on the flooding process was studied; for oil-unsaturated pores, three effects were modelled to investigate the oil/water phase flow behaviors, namely the wettability effect, the interfacial tension (IFT) effect, and the combined wettability/IFT effect. The results show that oil saturated pores with the water-wet state can lead to 25-40% more oil recovery than with the oil-wet state, and the remaining oil mainly stays in the near wall region of the pore bodies for oil-wet saturated pores. For oil-unsaturated pores, the wettability effects on the flooding process can help oil to detach from the pore walls. By decreasing the oil/water interfacial tension and altering the wettability from oil-wet to water-wet state, the remaining oil recovery rate can be enhanced successfully. The wettability-IFT combined effect shows better EOR potential compared with decreasing the interfacial tension alone under the oil-wet condition. The simulation results in this work are consistent with previous experimental and molecular dynamics simulation conclusions. The combination effect of the IFT reducation and wettability alteration can become an important recovery mechanism in future studies for nanoparticles, surfactant, and nanoparticle-surfactant hybrid flooding process.

Pore-scale simulation of wettability and interfacial tension effects on flooding process for enhanced oil recovery

PubMed Central

Zhao, Jin

2017-01-01

For enhanced oil recovery (EOR) applications, the oil/water flow characteristics during the flooding process was numerically investigated with the volume-of-fluid method at the pore scale. A two-dimensional pore throat-body connecting structure was established, and four scenarios were simulated in this paper. For oil-saturated pores, the wettability effect on the flooding process was studied; for oil-unsaturated pores, three effects were modelled to investigate the oil/water phase flow behaviors, namely the wettability effect, the interfacial tension (IFT) effect, and the combined wettability/IFT effect. The results show that oil saturated pores with the water-wet state can lead to 25–40% more oil recovery than with the oil-wet state, and the remaining oil mainly stays in the near wall region of the pore bodies for oil-wet saturated pores. For oil-unsaturated pores, the wettability effects on the flooding process can help oil to detach from the pore walls. By decreasing the oil/water interfacial tension and altering the wettability from oil-wet to water-wet state, the remaining oil recovery rate can be enhanced successfully. The wettability-IFT combined effect shows better EOR potential compared with decreasing the interfacial tension alone under the oil-wet condition. The simulation results in this work are consistent with previous experimental and molecular dynamics simulation conclusions. The combination effect of the IFT reducation and wettability alteration can become an important recovery mechanism in future studies for nanoparticles, surfactant, and nanoparticle–surfactant hybrid flooding process. PMID:29308190

Multi-Scale Porous Ultra High Temperature Ceramics

DTIC Science & Technology

2015-01-08

different techniques: replica, particle stabilized foams, ice templating (freeze casting) and partial sintering. The pore morphology (closed-bubble...the porosity, pore size, shape and morphology . X-Ray Tomography was used to study their 3D microstructure. The 3D microstructures captured with...four different techniques: replica, particle stabilized foams, ice templating (freeze casting) and partial sintering. The pore morphology (closed-bubble

A pore-scale study of fracture dynamics in rock using X-ray micro-CT under ambient freeze-thaw cycling.

PubMed

De Kock, Tim; Boone, Marijn A; De Schryver, Thomas; Van Stappen, Jeroen; Derluyn, Hannelore; Masschaele, Bert; De Schutter, Geert; Cnudde, Veerle

2015-03-03

Freeze-thaw cycling stresses many environments which include porous media such as soil, rock and concrete. Climate change can expose new regions and subject others to a changing freeze-thaw frequency. Therefore, understanding and predicting the effect of freeze-thaw cycles is important in environmental science, the built environment and cultural heritage preservation. In this paper, we explore the possibilities of state-of-the-art micro-CT in studying the pore scale dynamics related to freezing and thawing. The experiments show the development of a fracture network in a porous limestone when cooling to -9.7 °C, at which an exothermal temperature peak is a proxy for ice crystallization. The dynamics of the fracture network are visualized with a time frame of 80 s. Theoretical assumptions predict that crystallization in these experiments occurs in pores of 6-20.1 nm under transient conditions. Here, the crystallization-induced stress exceeds rock strength when the local crystal fraction in the pores is 4.3%. The location of fractures is strongly related to preferential water uptake paths and rock texture, which are visually identified. Laboratory, continuous X-ray micro-CT scanning opens new perspectives for the pore-scale study of ice crystallization in porous media as well as for environmental processes related to freeze-thaw fracturing.

Dynamic three-dimensional pore-scale imaging of reaction in a carbonate at reservoir conditions.

PubMed

Menke, Hannah P; Bijeljic, Branko; Andrew, Matthew G; Blunt, Martin J

2015-04-07

Quantifying CO2 transport and average effective reaction rates in the subsurface is essential to assess the risks associated with underground carbon capture and storage. We use X-ray microtomography to investigate dynamic pore structure evolution in situ at temperatures and pressures representative of underground reservoirs and aquifers. A 4 mm diameter Ketton carbonate core is injected with CO2-saturated brine at 50 °C and 10 MPa while tomographic images are taken at 15 min intervals with a 3.8 μm spatial resolution over a period of 2(1/2) h. An approximate doubling of porosity with only a 3.6% increase in surface area to volume ratio is measured from the images. Pore-scale direct simulation and network modeling on the images quantify an order of magnitude increase in permeability and an appreciable alteration of the velocity field. We study the uniform reaction regime, with dissolution throughout the core. However, at the pore scale, we see variations in the degree of dissolution with an overall reaction rate which is approximately 14 times lower than estimated from batch measurements. This work implies that in heterogeneous rocks, pore-scale transport of reactants limits dissolution and can reduce the average effective reaction rate by an order of magnitude.

A streamline splitting pore-network approach for computationally inexpensive and accurate simulation of transport in porous media

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mehmani, Yashar; Oostrom, Martinus; Balhoff, Matthew

2014-03-20

Several approaches have been developed in the literature for solving flow and transport at the pore-scale. Some authors use a direct modeling approach where the fundamental flow and transport equations are solved on the actual pore-space geometry. Such direct modeling, while very accurate, comes at a great computational cost. Network models are computationally more efficient because the pore-space morphology is approximated. Typically, a mixed cell method (MCM) is employed for solving the flow and transport system which assumes pore-level perfect mixing. This assumption is invalid at moderate to high Peclet regimes. In this work, a novel Eulerian perspective on modelingmore » flow and transport at the pore-scale is developed. The new streamline splitting method (SSM) allows for circumventing the pore-level perfect mixing assumption, while maintaining the computational efficiency of pore-network models. SSM was verified with direct simulations and excellent matches were obtained against micromodel experiments across a wide range of pore-structure and fluid-flow parameters. The increase in the computational cost from MCM to SSM is shown to be minimal, while the accuracy of SSM is much higher than that of MCM and comparable to direct modeling approaches. Therefore, SSM can be regarded as an appropriate balance between incorporating detailed physics and controlling computational cost. The truly predictive capability of the model allows for the study of pore-level interactions of fluid flow and transport in different porous materials. In this paper, we apply SSM and MCM to study the effects of pore-level mixing on transverse dispersion in 3D disordered granular media.« less

Transport upscaling from pore- to Darcy-scale: Incorporating pore-scale Berea sandstone Lagrangian velocity statistics into a Darcy-scale transport CTRW model

NASA Astrophysics Data System (ADS)

Puyguiraud, Alexandre; Dentz, Marco; Gouze, Philippe

2017-04-01

For the past several years a lot of attention has been given to pore-scale flow in order to understand and model transport, mixing and reaction in porous media. Nevertheless we believe that an accurate study of spatial and temporal evolution of velocities could bring important additional information for the upscaling from pore to higher scales. To gather these pieces of information, we perform Stokes flow simulations on pore-scale digitized images of a Berea sandstone core. First, micro-tomography (XRMT) imaging and segmentation processes allow us to obtain 3D black and white images of the sample [1]. Then we used an OpenFoam solver to perform the Stokes flow simulations mentioned above, which gives us the velocities at the interfaces of a cubic mesh. Subsequently, we use a particle streamline reconstruction technique which uses the Eulerian velocity field previously obtained. This technique, based on a modified Pollock algorithm [2], enables us to make particle tracking simulations on the digitized sample. In order to build a stochastic pore-scale transport model, we analyze the Lagrangian velocity series in two different ways. First we investigate the velocity evolution by sampling isochronically (t-Lagrangian), and by studying its statistical properties in terms of one- and two-points statistics. Intermittent patterns can be observed. These are due to the persistance of low velocities over a characteristic space length. Other results are investigated, such as correlation functions and velocity PDFs, which permit us to study more deeply this persistence in the velocities and to compute the correlation times. However, with the second approach, doing these same analysis in space by computing the velocities equidistantly, enables us to remove the intermittency shown in the temporal evolution and to model these velocity series as a Markov process. This renders the stochastic particle dynamics into a CTRW [3]. [1] Gjetvaj, F., A. Russian, P. Gouze, and M. Dentz (2015), Dual control of flow field heterogeneity and immobile porosity on non-Fickian transport in Berea sandstone, Water Resour. Res., 51, 8273-8293, doi:10.1002/2015WR017645. [2] Mostaghimi, P., Bijeljic, B., Blunt, M. (2012). Simulation of Flow and Dispersion on Pore-Space Images. Society of Petroleum Engineers. doi:10.2118/135261-PA. [3] Dentz, M., P. K. Kang, A. Comolli, T. Le Borgne, and D. R. Lester, Continuous time random walks for the evolution of Lagrangian velocities, Phys. Rev. Fluids, 2016. Keywords: Porescale, particle tracking, transport, Lagrangian velocity, ergodicity, Markovianity, continuous time random walks, upscaling.

Evaluation of Micro- and Macro-Scale Petrophysical Characteristics of Lower Cretaceous Sandstone with Flow Modeling in µ-CT Imaged Geometry

NASA Astrophysics Data System (ADS)

Katsman, R.; Haruzi, P.; Waldmann, N.; Halisch, M.

2017-12-01

In this study petrophysical characteristics of rock samples from 3 successive outcrop layers of Hatira Formation Lower Cretaceous Sandstone in northen Israel were evaluated at micro- and macro-scales. The study was carried out by two complementary methods: using conventional experimental measurements of porosity, pore size distribution and permeability; and using a 3D µCT imaging and modeling of signle-phase flow in the real micro-scale sample geometry. The workfow included µ-CT scanning, image processing, image segmentation, and image analyses of pore network, followed by fluid flow simulations at a pore-scale. Upscaling the results of the micro-scale flow simulations yielded a macroscopic permeabilty tensor. Comparison of the upscaled and the experimentally measured rock properties demonstrated a reasonable agreement. In addition, geometrical (pore size distribution, surface area and tortuosity) and topological (Euler characteristic) characteristics of the grains and of the pore network were evaluated at a micro-scale. Statistical analyses of the samples for estimation of anisotropy and inhomogeneity of the porous media were conducted and the results agree with anisotropy and inhomogeneity of the upscaled permeabilty tensor. Isotropic pore orientation of the primary inter-granular porosity was identified in all three samples, whereas the characteristics of the secondary porosity were affected by precipitated cement and clay matrix within the primary pore network. Results of this study provide micro- and macro-scale characteristics of the Lower Cretaceous sandstone that is used in different places over the world as a reservoir for petroleum production and sequestration.

Pore-scale study of multiphase reactive transport in fibrous electrodes of vanadium redox flow batteries

DOE PAGES

Chen, Li; He, YaLing; Tao, Wen -Quan; ...

2017-07-21

The electrode of a vanadium redox flow battery generally is a carbon fibre-based porous medium, in which important physicochemical processes occur. In this work, pore-scale simulations are performed to study complex multiphase flow and reactive transport in the electrode by using the lattice Boltzmann method (LBM). Four hundred fibrous electrodes with different fibre diameters and porosities are reconstructed. Both the permeability and diffusivity of the reconstructed electrodes are predicted and compared with empirical relationships in the literature. Reactive surface area of the electrodes is also evaluated and it is found that existing empirical relationship overestimates the reactive surface under lowermore » porosities. Further, a pore-scale electrochemical reaction model is developed to study the effects of fibre diameter and porosity on electrolyte flow, V II/V III transport, and electrochemical reaction at the electrolyte-fibre surface. Finally, evolution of bubble cluster generated by the side reaction is studied by adopting a LB multiphase flow model. Effects of porosity, fibre diameter, gas saturation and solid surface wettability on average bubble diameter and reduction of reactive surface area due to coverage of bubbles on solid surface are investigated in detail. It is found that gas coverage ratio is always lower than that adopted in the continuum model in the literature. Furthermore, the current pore-scale studies successfully reveal the complex multiphase flow and reactive transport processes in the electrode, and the simulation results can be further upscaled to improve the accuracy of the current continuum-scale models.« less

Application of a pore-scale reactive transport model to a natural analog for reaction-induced pore alterations

DOE PAGES

Yoon, Hongkyu; Major, Jonathan; Dewers, Thomas; ...

2017-01-05

Dissolved CO 2 in the subsurface resulting from geological CO 2 storage may react with minerals in fractured rocks, confined aquifers, or faults, resulting in mineral precipitation and dissolution. The overall rate of reaction can be affected by coupled processes including hydrodynamics, transport, and reactions at the (sub) pore-scale. In this work pore-scale modeling of coupled fluid flow, reactive transport, and heterogeneous reactions at the mineral surface is applied to account for permeability alterations caused by precipitation-induced pore-blocking. This paper is motivated by observations of CO 2 seeps from a natural CO 2 sequestration analog, Crystal Geyser, Utah. Observations alongmore » the surface exposure of the Little Grand Wash fault indicate the lateral migration of CO 2 seep sites (i.e., alteration zones) of 10–50 m width with spacing on the order of ~100 m over time. Sandstone permeability in alteration zones is reduced by 3–4 orders of magnitude by carbonate cementation compared to unaltered zones. One granular porous medium and one fracture network systems are used to conceptually represent permeable porous media and locations of conduits controlled by fault-segment intersections and/or topography, respectively. Simulation cases accounted for a range of reaction regimes characterized by the Damköhler (Da) and Peclet (Pe) numbers. Pore-scale simulation results demonstrate that combinations of transport (Pe), geochemical conditions (Da), solution chemistry, and pore and fracture configurations contributed to match key patterns observed in the field of how calcite precipitation alters flow paths by pore plugging. This comparison of simulation results with field observations reveals mechanistic explanations of the lateral migration and enhances our understanding of subsurface processes associated with the CO 2 injection. In addition, permeability and porosity relations are constructed from pore-scale simulations which account for a range of reaction regimes characterized by the Da and Pe numbers. Finally, the functional relationships obtained from pore-scale simulations can be used in a continuum scale model that may account for large-scale phenomena mimicking lateral migration of surface CO 2 seeps.« less

Pore-scale and Continuum Simulations of Solute Transport Micromodel Benchmark Experiments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Oostrom, Martinus; Mehmani, Yashar; Romero Gomez, Pedro DJ

Four sets of micromodel nonreactive solute transport experiments were conducted with flow velocity, grain diameter, pore-aspect ratio, and flow focusing heterogeneity as the variables. The data sets were offered to pore-scale modeling groups to test their simulators. Each set consisted of two learning experiments, for which all results was made available, and a challenge experiment, for which only the experimental description and base input parameters were provided. The experimental results showed a nonlinear dependence of the dispersion coefficient on the Peclet number, a negligible effect of the pore-aspect ratio on transverse mixing, and considerably enhanced mixing due to flow focusing.more » Five pore-scale models and one continuum-scale model were used to simulate the experiments. Of the pore-scale models, two used a pore-network (PN) method, two others are based on a lattice-Boltzmann (LB) approach, and one employed a computational fluid dynamics (CFD) technique. The learning experiments were used by the PN models to modify the standard perfect mixing approach in pore bodies into approaches to simulate the observed incomplete mixing. The LB and CFD models used these experiments to appropriately discretize the grid representations. The continuum model use published non-linear relations between transverse dispersion coefficients and Peclet numbers to compute the required dispersivity input values. Comparisons between experimental and numerical results for the four challenge experiments show that all pore-scale models were all able to satisfactorily simulate the experiments. The continuum model underestimated the required dispersivity values and, resulting in less dispersion. The PN models were able to complete the simulations in a few minutes, whereas the direct models needed up to several days on supercomputers to resolve the more complex problems.« less

Pore-Fractal Structure in Porous Carbons Made from Corn and Wheat

NASA Astrophysics Data System (ADS)

Kapoor, Y. M.; Schmidt, P. W.; Rice, Randall D.; Shulse, Laural; Voss, D. J.; Venkatraman, A.; Fan, L. T.; Walawender, W. P.; Rieker, T. P.

1998-03-01

Small-angle X-ray scattering has been used in a study of the pore structure of some porous and activated carbons on length scales between about 5 and 10^4 ÅThe carbons were obtained by pyrolysis and activation of wheat and American corn (maize). The scattering data showed that in each carbon there are at least two of the following four types of pores: (1) pores with diameters of at least 10^4 Åpores with smooth or fractal surfaces and diameters of at least 5 x 10^3 Åpore-fractals with diameters of no more than about 10^3 Åand (4) pores with diameters no larger than 100 ÅThe relation between the pore structure and the procedure used to obtain the carbon and will be discussed.

Visualizing and Quantifying Pore Scale Fluid Flow Processes With X-ray Microtomography

NASA Astrophysics Data System (ADS)

Wildenschild, D.; Hopmans, J. W.; Vaz, C. M.; Rivers, M. L.

2001-05-01

When using mathematical models based on Darcy's law it is often necessary to simplify geometry, physics or both and the capillary bundle-of-tubes approach neglects a fundamentally important characteristic of porous solids, namely interconnectedness of the pore space. New approaches to pore-scale modeling that arrange capillary tubes in two- or three-dimensional pore space have been and are still under development: Network models generally represent the pore space by spheres while the pore throats are usually represented by cylinders or conical shapes. Lattice Boltzmann approaches numerically solve the Navier-Stokes equations in a realistic microscopically disordered geometry, which offers the ability to study the microphysical basis of macroscopic flow without the need for a simplified geometry or physics. In addition to these developments in numerical modeling techniques, new theories have proposed that interfacial area should be considered as a primary variable in modeling of a multi-phase flow system. In the wake of this progress emerges an increasing need for new ways of evaluating pore-scale models, and for techniques that can resolve and quantify phase interfaces in porous media. The mechanisms operating at the pore-scale cannot be measured with traditional experimental techniques, however x-ray computerized microtomography (CMT) provides non-invasive observation of, for instance, changing fluid phase content and distribution on the pore scale. Interfacial areas have thus far been measured indirectly, but with the advances in high-resolution imaging using CMT it is possible to track interfacial area and curvature as a function of phase saturation or capillary pressure. We present results obtained at the synchrotron-based microtomography facility (GSECARS, sector 13) at the Advanced Photon Source at Argonne National Laboratory. Cylindrical sand samples of either 6 or 1.5 mm diameter were scanned at different stages of drainage and for varying boundary conditions. A significant difference in fluid saturation and phase distribution was observed for different drainage conditions, clearly showing preferential flow and a dependence on the applied flow rate. For the 1.5 mm sample individual pores and water/air interfaces could be resolved and quantified using image analysis techniques. Use of the Advanced Photon Source was supported by the U.S. Department of Energy, Basic Energy Sciences, Office of Science, under Contract No. W-31-109-Eng-38.

Multiscale pore structure and constitutive models of fine-grained rocks

NASA Astrophysics Data System (ADS)

Heath, J. E.; Dewers, T. A.; Shields, E. A.; Yoon, H.; Milliken, K. L.

2017-12-01

A foundational concept of continuum poromechanics is the representative elementary volume or REV: an amount of material large enough that pore- or grain-scale fluctuations in relevant properties are dissipated to a definable mean, but smaller than length scales of heterogeneity. We determine 2D-equivalent representative elementary areas (REAs) of pore areal fraction of three major types of mudrocks by applying multi-beam scanning electron microscopy (mSEM) to obtain terapixel image mosaics. Image analysis obtains pore areal fraction and pore size and shape as a function of progressively larger measurement areas. Using backscattering imaging and mSEM data, pores are identified by the components within which they occur, such as in organics or the clastic matrix. We correlate pore areal fraction with nano-indentation, micropillar compression, and axysimmetic testing at multiple length scales on a terrigenous-argillaceous mudrock sample. The combined data set is used to: investigate representative elementary volumes (and areas for the 2D images); determine if scale separation occurs; and determine if transport and mechanical properties at a given length scale can be statistically defined. Clear scale separation occurs between REAs and observable heterogeneity in two of the samples. A highly-laminated sample exhibits fine-scale heterogeneity and an overlapping in scales, in which case typical continuum assumptions on statistical variability may break down. Sandia National Laboratories is a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia LLC, a wholly owned subsidiary of Honeywell International Inc. for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-NA0003525.

Pore-scale simulation of calcium carbonate precipitation and dissolution under highly supersaturated conditions in a microfludic pore network

NASA Astrophysics Data System (ADS)

Yoon, H.; Dewers, T. A.; Valocchi, A. J.; Werth, C. J.

2011-12-01

Dissolved CO2 during geological CO2 storage may react with minerals in fractured rocks or confined aquifers and cause mineral precipitation. The overall rate of reaction can be affected by coupled processes among hydrodynamics, transport, and reactions at pore-scale. Pore-scale models of coupled fluid flow, reactive transport, and CaCO3 precipitation and dissolution are applied to account for transient experimental results of CaCO3 precipitation and dissolution under highly supersaturated conditions in a microfluidic pore network (i.e., micromodel). Pore-scale experiments in the micromodel are used as a basis for understanding coupled physics of systems perturbed by geological CO2 injection. In the micromodel, precipitation is induced by transverse mixing along the centerline in pore bodies. Overall, the pore-scale model qualitatively captured the governing physics of reactions such as precipitate morphology, precipitation rate, and maximum precipitation area in first few pore spaces. In particular, we found that proper estimation of the effective diffusion coefficient and the reactive surface area is necessary to adequately simulate precipitation and dissolution rates. As the model domain increases, the effect of flow patterns affected by precipitation on the overall reaction rate also increases. The model is also applied to account for the effect of different reaction rate laws on mineral precipitation and dissolution at pore-scale. Reaction rate laws tested include the linear rate law, nonlinear power law, and newly-developed rate law based on in-situ measurements at nano scale in the literature. Progress on novel methods for upscaling pore-scale models for reactive transport are discussed, and are being applied to mineral precipitation patterns observed in natural analogues. H.Y. and T. D. were supported as part of the Center for Frontiers of Subsurface Energy Security, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award Number DE-SC0001114. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

Experimental Study of Porosity Changes in Shale Caprocks Exposed to CO 2-Saturated Brines I: Evolution of Mineralogy, Pore Connectivity, Pore Size Distribution, and Surface Area

DOE PAGES

Mouzakis, Katherine M.; Navarre-Sitchler, Alexis K.; Rother, Gernot; ...

2016-07-18

Carbon capture, utilization, and storage, one proposed method of reducing anthropogenic emissions of CO 2, relies on low permeability formations, such as shales, above injection formations to prevent upward migration of the injected CO 2. Porosity in caprocks evaluated for sealing capacity before injection can be altered by geochemical reactions induced by dissolution of injected CO 2 into pore fluids, impacting long-term sealing capacity. Therefore, long-term performance of CO 2 sequestration sites may be dependent on both initial distribution and connectivity of pores in caprocks, and on changes induced by geochemical reaction after injection of CO 2, which are currentlymore » poorly understood. This paper presents results from an experimental study of changes to caprock porosity and pore network geometry in two caprock formations under conditions relevant to CO 2 sequestration. Pore connectivity and total porosity increased in the Gothic Shale; while total porosity increased but pore connectivity decreased in the Marine Tuscaloosa. Gothic Shale is a carbonate mudstone that contains volumetrically more carbonate minerals than Marine Tuscaloosa. Carbonate minerals dissolved to a greater extent than silicate minerals in Gothic Shale under high CO 2 conditions, leading to increased porosity at length scales <~200 nm that contributed to increased pore connectivity. In contrast, silicate minerals dissolved to a greater extent than carbonate minerals in Marine Tuscaloosa leading to increased porosity at all length scales, and specifically an increase in the number of pores >~1 μm. Mineral reactions also contributed to a decrease in pore connectivity, possibly as a result of precipitation in pore throats or hydration of the high percentage of clays. Finally, this study highlights the role that mineralogy of the caprock can play in geochemical response to CO 2 injection and resulting changes in sealing capacity in long-term CO 2 storage projects.« less

Multiscale modelling of dual-porosity porous media; a computational pore-scale study for flow and solute transport

NASA Astrophysics Data System (ADS)

de Vries, Enno T.; Raoof, Amir; van Genuchten, Martinus Th.

2017-07-01

Many environmental and agricultural applications involve the transport of water and dissolved constituents through aggregated soil profiles, or porous media that are structured, fractured or macroporous in other ways. During the past several decades, various process-based macroscopic models have been used to simulate contaminant transport in such media. Many of these models consider advective-dispersive transport through relatively large inter-aggregate pore domains, while exchange with the smaller intra-aggregate pores is assumed to be controlled by diffusion. Exchange of solute between the two domains is often represented using a first-order mass transfer coefficient, which is commonly obtained by fitting to observed data. This study aims to understand and quantify the solute exchange term by applying a dual-porosity pore-scale network model to relatively large domains, and analysing the pore-scale results in terms of the classical dual-porosity (mobile-immobile) transport formulation. We examined the effects of key parameters (notably aggregate porosity and aggregate permeability) on the main dual-porosity model parameters, i.e., the mobile water fraction (ϕm) and the mass transfer coefficient (α). Results were obtained for a wide range of aggregate porosities (between 0.082 and 0.700). The effect of aggregate permeability was explored by varying pore throat sizes within the aggregates. Solute breakthrough curves (BTCs) obtained with the pore-scale network model at several locations along the domain were analysed using analytical solutions of the dual-porosity model to obtain estimates of ϕm and α. An increase in aggregate porosity was found to decrease ϕm and increase α, leading to considerable tailing in the BTCs. Changes in the aggregate pore throat size affected the relative flow velocity between the intra- and inter-aggregate domains. Higher flow velocities within the aggregates caused a change in the transport regime from diffusion dominated to more advection dominated. This change increased the exchange rate of solutes between the mobile and immobile domains, with a related increase in the value of the mass transfer coefficient and less tailing in the BTCs.

VISUALIZATION AND SIMULATION OF NON-AQUEOUS PHASE LIQUIDS SOLUBILIZATION IN PORE NETWORKS

EPA Science Inventory

The design of in-situ remediation of contaminated soils is mostly based on a description at the macroscopic scale using a averaged quantities. These cannot address issues at the pore and pore network scales. In this paper, visualization experiments and numerical simulations in ...

On the predictivity of pore-scale simulations: Estimating uncertainties with multilevel Monte Carlo

NASA Astrophysics Data System (ADS)

Icardi, Matteo; Boccardo, Gianluca; Tempone, Raúl

2016-09-01

A fast method with tunable accuracy is proposed to estimate errors and uncertainties in pore-scale and Digital Rock Physics (DRP) problems. The overall predictivity of these studies can be, in fact, hindered by many factors including sample heterogeneity, computational and imaging limitations, model inadequacy and not perfectly known physical parameters. The typical objective of pore-scale studies is the estimation of macroscopic effective parameters such as permeability, effective diffusivity and hydrodynamic dispersion. However, these are often non-deterministic quantities (i.e., results obtained for specific pore-scale sample and setup are not totally reproducible by another ;equivalent; sample and setup). The stochastic nature can arise due to the multi-scale heterogeneity, the computational and experimental limitations in considering large samples, and the complexity of the physical models. These approximations, in fact, introduce an error that, being dependent on a large number of complex factors, can be modeled as random. We propose a general simulation tool, based on multilevel Monte Carlo, that can reduce drastically the computational cost needed for computing accurate statistics of effective parameters and other quantities of interest, under any of these random errors. This is, to our knowledge, the first attempt to include Uncertainty Quantification (UQ) in pore-scale physics and simulation. The method can also provide estimates of the discretization error and it is tested on three-dimensional transport problems in heterogeneous materials, where the sampling procedure is done by generation algorithms able to reproduce realistic consolidated and unconsolidated random sphere and ellipsoid packings and arrangements. A totally automatic workflow is developed in an open-source code [1], that include rigid body physics and random packing algorithms, unstructured mesh discretization, finite volume solvers, extrapolation and post-processing techniques. The proposed method can be efficiently used in many porous media applications for problems such as stochastic homogenization/upscaling, propagation of uncertainty from microscopic fluid and rock properties to macro-scale parameters, robust estimation of Representative Elementary Volume size for arbitrary physics.

A multi-scale network method for two-phase flow in porous media

DOE Office of Scientific and Technical Information (OSTI.GOV)

Khayrat, Karim, E-mail: khayratk@ifd.mavt.ethz.ch; Jenny, Patrick

Pore-network models of porous media are useful in the study of pore-scale flow in porous media. In order to extract macroscopic properties from flow simulations in pore-networks, it is crucial the networks are large enough to be considered representative elementary volumes. However, existing two-phase network flow solvers are limited to relatively small domains. For this purpose, a multi-scale pore-network (MSPN) method, which takes into account flow-rate effects and can simulate larger domains compared to existing methods, was developed. In our solution algorithm, a large pore network is partitioned into several smaller sub-networks. The algorithm to advance the fluid interfaces withinmore » each subnetwork consists of three steps. First, a global pressure problem on the network is solved approximately using the multiscale finite volume (MSFV) method. Next, the fluxes across the subnetworks are computed. Lastly, using fluxes as boundary conditions, a dynamic two-phase flow solver is used to advance the solution in time. Simulation results of drainage scenarios at different capillary numbers and unfavourable viscosity ratios are presented and used to validate the MSPN method against solutions obtained by an existing dynamic network flow solver.« less

Using synchrotron-based X-ray micro-computed tomography and high-performance pore-scale simulation to evaluate hydraulic properties in biochar-amended soils

NASA Astrophysics Data System (ADS)

Zhou, H.; Yu, X.; Chen, C.; Zeng, L.; Lu, S.; Wu, L.

2016-12-01

In this research, we combined synchrotron-based X-ray micro-computed tomography (SR-mCT), with three-dimensional lattice Bolzmann (LB) method, to quantify how the change in pore space architecture affected macroscopic hydraulic of two clayey soils amended with biochar. SR-mCT was used to characterize pore structures of the soils before and after biochar addition. The high-resolution soil pore structures were then directly used as internal boundary conditions for three-dimensional water flow simulations with the LB method, which was accelerated by graphics processing unit (GPU) parallel computing. It was shown that, due to the changes in soil pore geometry, the application of biochar increased the soil permeability by at least 1 order of magnitude, and decreased the tortuosity by 20-30%. This work was the first physics based modeling study on the effect of biochar amendment on soil hydraulic properties. The developed theories and techniques have promising potential in understanding the mechanisms of water and nutrient transport in soil at the pore scale.

Investigation of Biogrout processes by numerical analysis at pore scale

NASA Astrophysics Data System (ADS)

Bergwerff, Luke; van Paassen, Leon A.; Picioreanu, Cristian; van Loosdrecht, Mark C. M.

2013-04-01

Biogrout is a soil improving process that aims to improve the strength of sandy soils. The process is based on microbially induced calcite precipitation (MICP). In this study the main process is based on denitrification facilitated by bacteria indigenous to the soil using substrates, which can be derived from pretreated waste streams containing calcium salts of fatty acids and calcium nitrate, making it a cost effective and environmentally friendly process. The goal of this research is to improve the understanding of the process by numerical analysis so that it may be improved and applied properly for varying applications, such as borehole stabilization, liquefaction prevention, levee fortification and mitigation of beach erosion. During the denitrification process there are many phases present in the pore space including a liquid phase containing solutes, crystals, bacteria forming biofilms and gas bubbles. Due to the amount of phases and their dynamic changes (multiphase flow with (non-linear) reactive transport), there are many interactions making the process very complex. To understand this complexity in the system, the interactions between these phases are studied in a reductionist approach, increasing the complexity of the system by one phase at a time. The model will initially include flow, solute transport, crystal nucleation and growth in 2D at pore scale. The flow will be described by Navier-Stokes equations. Initial study and simulations has revealed that describing crystal growth for this application on a fixed grid can introduce significant fundamental errors. Therefore a level set method will be employed to better describe the interface of developing crystals in between sand grains. Afterwards the model will be expanded to 3D to provide more realistic flow, nucleation and clogging behaviour at pore scale. Next biofilms and lastly gas bubbles may be added to the model. From the results of these pore scale models the behaviour of the system may be studied and eventually observations may be extrapolated to a larger continuum scale.

Determining Representative Elementary Volume For Multiple Petrophysical Parameters using a Convex Hull Analysis of Digital Rock Data

NASA Astrophysics Data System (ADS)

Shah, S.; Gray, F.; Yang, J.; Crawshaw, J.; Boek, E.

2016-12-01

Advances in 3D pore-scale imaging and computational methods have allowed an exceptionally detailed quantitative and qualitative analysis of the fluid flow in complex porous media. A fundamental problem in pore-scale imaging and modelling is how to represent and model the range of scales encountered in porous media, starting from the smallest pore spaces. In this study, a novel method is presented for determining the representative elementary volume (REV) of a rock for several parameters simultaneously. We calculate the two main macroscopic petrophysical parameters, porosity and single-phase permeability, using micro CT imaging and Lattice Boltzmann (LB) simulations for 14 different porous media, including sandpacks, sandstones and carbonates. The concept of the `Convex Hull' is then applied to calculate the REV for both parameters simultaneously using a plot of the area of the convex hull as a function of the sub-volume, capturing the different scales of heterogeneity from the pore-scale imaging. The results also show that the area of the convex hull (for well-chosen parameters such as the log of the permeability and the porosity) decays exponentially with sub-sample size suggesting a computationally efficient way to determine the system size needed to calculate the parameters to high accuracy (small convex hull area). Finally we propose using a characteristic length such as the pore size to choose an efficient absolute voxel size for the numerical rock.

Comparison of Pore-Network and Lattice Boltzmann Models for Pore-Scale Modeling of Geological Storage of CO2 in Natural Reservoir Rocks

NASA Astrophysics Data System (ADS)

Kohanpur, A. H.; Chen, Y.; Valocchi, A. J.; Tudek, J.; Crandall, D.

2016-12-01

CO2-brine flow in deep natural rocks is the focus of attention in geological storage of CO2. Understanding rock/flow properties at pore-scale is a vital component in field-scale modeling and prediction of fate of injected CO2. There are many challenges in working at the pore scale, such as size and selection of representative elementary volume (REV), particularly for material with complex geometry and heterogeneity, and the high computational costs. These issues factor into trade-offs that need to be made in choosing and applying pore-scale models. On one hand, pore-network modeling (PNM) simplifies the geometry and flow equations but can provide characteristic curves on fairly large samples. On the other hand, the lattice Boltzmann method (LBM) solves Navier-Stokes equations on the real geometry but is limited to small samples due to its high computational costs. Thus, both methods have some advantages but also face some challenges, which warrants a more detailed comparison and evaluation. In this study, we used industrial and micro-CT scans of actual reservoir rock samples to characterize pore structure at different resolutions. We ran LBM models directly on the characterized geometry and PNM on the equivalent 3D extracted network to determine single/two-phase flow properties during drainage and imbibition processes. Specifically, connectivity, absolute permeability, relative permeability curve, capillary pressure curve, and interface location are compared between models. We also did simulations on several subsamples from different locations including different domain sizes and orientations to encompass analysis of heterogeneity and isotropy. This work is primarily supported as part of the Center for Geologic Storage of CO2, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science and partially supported by the International Institute for Carbon-Neutral Energy Research (WPI-I2CNER) based at Kyushu University, Japan.

Understanding fluid transport through the multiscale pore network of a natural shale

NASA Astrophysics Data System (ADS)

Davy, Catherine; Adler, Pierre; Song, Yang; Nguyen, Thang Kim; Troadec, David; Dhénin, Jean-Francois

2017-04-01

Natural shales have a complex pore structure, which is only partly understood today. In the present contribution, a combination of different techniques is used to get information on three different scales. On each scale, the relevant flow equation is solved and provides input for the flow equation of the next higher scale. More precisely, micro-CT, FIB/SEM (Focused Ion Beam/Scanning Electron Microscopy) and TEM (Transmission Electron Microscopy) provide a full representative 3D pore space on the macroscopic scale, the mesoscale and the nanoscale. The corresponding typical voxel sizes are 0.7 μm, 10 nm and 1 nm, respectively. The porosity on the micro-CT images is 0.5 %, and it is not connected. One can distinguish between the pores, the porous clay matrix and non porous minerals; the volume percentages of these last two phases are 0.6 and 0.395, respectively. Samples of the porous clay matrix were analyzed by FIB/SEM which yields 3D information. They have a porosity ranging from 2 to 6 %. In some of them, the pore space is connected. Finally, TEM provides 2D images with a porosity of about 10 to 25 %. These information were used in the following way to estimate the macroscopic permeability which has been measured independently and found equal to 6 x10-20 m2. At the nanoscopic scale analyzed by 2D TEM, in the absence of 3D images, the pore structure is reconstructed by using a technique based on truncated Gaussian fields. Then, the Stokes equations are solved by using a 3D Lattice Boltzmann method. The resulting velocity field is averaged and this provides the permeability K_n. The permeability of the nanoscale structure varies between 0.7x 10-20 and 1.8x10-19 m2. As expected, the material is anisotropic. At the mesoscale, percolation of the FIB/SEM pore volume occurs only along a single direction. The Stokes equations are again solved by the same method and the mesoscopic permeability Km varies between 3.3 10-20 and 1.20 10-18 m2, depending on the nature of the percolating volume. The influence of the nanoscale porosity on the mesoscopic permeability is also studied. Two examples show that despite the scale ratio between the mesoscopic and nanoscopic pores, the nanoscopic pore structure cannot be neglected to estimate the permeability of the pore clay matrix. Finally, the sample provided by micro-CT is considered as a porous medium composed of three phases with permeabilities 0 (for the non porous minerals), 1 (for the porous clay matrix) and infinity (for the macroscopic pores). The overall permeability Kmacro is obtained by solving the Darcy's equation with a variable local permeability with spatially periodic boundary conditions. Kmacro is found of the order of 0.4 and the medium is relatively isotropic on this scale. This estimation of Kmacro is in agreement with the measured value.

Understanding fluid transport through the multiscale pore network of a natural shale

NASA Astrophysics Data System (ADS)

Davy, Catherine A.; Nguyen Kim, Thang; Song, Yang; Troadec, David; Blanchenet, Anne-Marie; Adler, Pierre M.

2017-06-01

The pore structure of a natural shale is obtained by three imaging means. Micro-tomography results are extended to provide the spatial arrangement of the minerals and pores present at a voxel size of 700 nm (the macroscopic scale). FIB/SEM provides a 3D representation of the porous clay matrix on the so-called mesoscopic scale (10-20 nm); a connected pore network, devoid of cracks, is obtained for two samples out of five, while the pore network is connected through cracks for two other samples out of five. Transmission Electron Microscopy (TEM) is used to visualize the pore space with a typical pixel size of less than 1 nm and a porosity ranging from 0.12 to 0.25. On this scale, in the absence of 3D images, the pore structure is reconstructed by using a classical technique, which is based on truncated Gaussian fields. Permeability calculations are performed with the Lattice Boltzmann Method on the nanoscale, on the mesoscale, and on the combination of the two. Upscaling is finally done (by a finite volume approach) on the bigger macroscopic scale. Calculations show that, in the absence of cracks, the contribution of the nanoscale pore structure on the overall permeability is similar to that of the mesoscale. Complementarily, the macroscopic permeability is measured on a centimetric sample with a neutral fluid (ethanol). The upscaled permeability on the macroscopic scale is in good agreement with the experimental results.

2D and 3D characterization of pore defects in die cast AM60

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yang, Zhuofei; CanmetMATERIALS, 183 Longwood Road South, Hamilton L8P 0A5, Ontario Canada; Maurey, Alexandre

2016-04-15

The widespread application of die castings can be hampered due to the potential of large scale porosity to act as nucleation sites for fracture and fatigue. It is therefore important to develop robust approaches to the characterization of porosity providing parameters that can be linked to the material's mechanical properties. We have tackled this problem in a study of the AM60 die cast Mg alloy, using samples extracted from a prototype shock tower. A quantitative characterization of porosity has been undertaken, analyzing porosity in both 2D (using classical metallographic methods) and in 3D (using X-ray computed tomography (XCT)). Metallographic characterizationmore » results show that shrinkage pores and small gas pores can be distinguished based on their distinct geometrical features. Shrinkage pores are irregular with multiple arms, resulting in a form factor less than 0.4. In contrast, gas pores are generally more circular in shape yielding form factors larger than 0.6. XCT provides deeper insight into the shape of pores, although this understanding is limited by the resolution obtainable by laboratory based XCT. It also shows how 2D sectioning can produce artefacts as single complex pores are sectioned into multiple small pores. - Highlights: • Mg (e.g. AM60) die castings may contain large scale porosity that act as nucleation sites for fracture and fatigue • Quantitative characterization of porosity metallography (2D) and X-ray tomography (3D) is used • Shrinkage pores and small gas pores can be distinguished based on their distinct geometrical features. • Shrinkage pores are irregular giving a form factor < 0.4; gas pores are rounder with form factors > 0.6 • XCT enables pore visualization, although limited by the resolution obtainable by laboratory based XCT.« less

Multiscale Simulation of Porous Ceramics Based on Movable Cellular Automaton Method

NASA Astrophysics Data System (ADS)

Smolin, A.; Smolin, I.; Eremina, G.; Smolina, I.

2017-10-01

The paper presents a model for simulating mechanical behaviour of multiscale porous ceramics based on movable cellular automaton method, which is a novel particle method in computational mechanics of solid. The initial scale of the proposed approach corresponds to the characteristic size of the smallest pores in the ceramics. At this scale, we model uniaxial compression of several representative samples with an explicit account of pores of the same size but with the random unique position in space. As a result, we get the average values of Young’s modulus and strength, as well as the parameters of the Weibull distribution of these properties at the current scale level. These data allow us to describe the material behaviour at the next scale level were only the larger pores are considered explicitly, while the influence of small pores is included via the effective properties determined at the previous scale level. If the pore size distribution function of the material has N maxima we need to perform computations for N - 1 levels in order to get the properties from the lowest scale up to the macroscale step by step. The proposed approach was applied to modelling zirconia ceramics with bimodal pore size distribution. The obtained results show correct behaviour of the model sample at the macroscale.

Characterization of nanoporous shales with gas sorption

NASA Astrophysics Data System (ADS)

Joewondo, N.; Prasad, M.

2017-12-01

The understanding of the fluid flow in porous media requires the knowledge of the pore system involved. Fluid flow in fine grained shales falls under different regime than transport regime in conventional reservoir due to the different average pore sizes in the two materials; the average pore diameter of conventional sandstones is on the micrometer scale, while of shales can be as small as several nanometers. Mercury intrusion porosimetry is normally used to characterize the pores of conventional reservoir, however with increasingly small pores, the injection pressure required to imbibe the pores becomes infinitely large due to surface tension. Characterization of pores can be expressed by a pore size distribution (PSD) plot, which reflects distribution of pore volume or surface area with respect to pore size. For the case of nanoporous materials, the surface area, which serves as the interface between the rock matrix and fluid, becomes increasingly large and important. Physisorption of gas has been extensively studied as a method of nanoporous solid characterization (particularly for the application of catalysis, metal organic frameworks, etc). The PSD is obtained by matching the experimental result to the calculated theoretical result (using Density Functional Theory (DFT), a quantum mechanics based modelling method for molecular scale interactions). We present the challenges and experimental result of Nitrogen and CO2 gas sorption on shales with various mineralogy and the interpreted PSD obtained by DFT method. Our result shows significant surface area contributed by the nanopores of shales, hence the importance of surface area measurements for the characterization of shales.

Multiscale modeling of porous ceramics using movable cellular automaton method

NASA Astrophysics Data System (ADS)

Smolin, Alexey Yu.; Smolin, Igor Yu.; Smolina, Irina Yu.

2017-10-01

The paper presents a multiscale model for porous ceramics based on movable cellular automaton method, which is a particle method in novel computational mechanics of solid. The initial scale of the proposed approach corresponds to the characteristic size of the smallest pores in the ceramics. At this scale, we model uniaxial compression of several representative samples with an explicit account of pores of the same size but with the unique position in space. As a result, we get the average values of Young's modulus and strength, as well as the parameters of the Weibull distribution of these properties at the current scale level. These data allow us to describe the material behavior at the next scale level were only the larger pores are considered explicitly, while the influence of small pores is included via effective properties determined earliar. If the pore size distribution function of the material has N maxima we need to perform computations for N-1 levels in order to get the properties step by step from the lowest scale up to the macroscale. The proposed approach was applied to modeling zirconia ceramics with bimodal pore size distribution. The obtained results show correct behavior of the model sample at the macroscale.

Upscaling of reaction rates in reactive transport using pore-scale reactive transport model

NASA Astrophysics Data System (ADS)

Yoon, H.; Dewers, T. A.; Arnold, B. W.; Major, J. R.; Eichhubl, P.; Srinivasan, S.

2013-12-01

Dissolved CO2 during geological CO2 storage may react with minerals in fractured rocks, confined aquifers, or faults, resulting in mineral precipitation and dissolution. The overall rate of reaction can be affected by coupled processes among hydrodynamics, transport, and reactions at the (sub) pore-scale. In this research pore-scale modeling of coupled fluid flow, reactive transport, and heterogeneous reaction at the mineral surface is applied to account for permeability alterations caused by precipitation-induced pore-blocking. This work is motivated by the observed CO2 seeps from a natural analog to geologic CO2 sequestration at Crystal Geyser, Utah. A key observation is the lateral migration of CO2 seep sites at a scale of ~ 100 meters over time. A pore-scale model provides fundamental mechanistic explanations of how calcite precipitation alters flow paths by pore plugging under different geochemical compositions and pore configurations. In addition, response function of reaction rates will be constructed from pore-scale simulations which account for a range of reaction regimes characterized by the Damkohler and Peclet numbers. Newly developed response functions will be used in a continuum scale model that may account for large-scale phenomena mimicking lateral migration of surface CO2 seeps. Comparison of field observations and simulations results will provide mechanistic explanations of the lateral migration and enhance our understanding of subsurface processes associated with the CO2 injection. This work is supported as part of the Center for Frontiers of Subsurface Energy Security, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award Number DE-SC0001114. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

Laboratory measurements of shock propagation through spherical cavities in an optically accessible polymer.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chojnicki, Kirsten; Cooper, Marcia A.; Guo, Shuyue

Pore-scale aperture effects on flow in pore networks was studied in the laboratory to provide a parameterization for use in transport models. Four cases were considered: regular and irregular pillar/pore alignment with and without an aperture. The velocity field of each case was measured and simulated, providing quantitatively comparable results. Two aperture effect parameterizations were considered: permeability and transmission. Permeability values varied by an order of magnitude between the cases with and without apertures. However, transmission did not correlate with permeability. Despite having much greater permeability the regular aperture case permitted less transmission than the regular case. Moreover, both irregularmore » cases had greater transmission than the regular cases, a difference not supported by the permeabilities. Overall, these findings suggest that pore-scale aperture effects on flow though a pore-network may not be adequately captured by properties such as permeability for applications that are interested in determining particle transport volume and timing.« less

Pore-scale study of effects of macroscopic pores and their distributions on reactive transport in hierarchical porous media

DOE PAGES

Chen, Li; Zhang, Ruiyuan; Min, Ting; ...

2018-05-19

For applications of reactive transport in porous media, optimal porous structures should possess both high surface area for reactive sites loading and low mass transport resistance. Hierarchical porous media with a combination of pores at different scales are designed for this purpose. In this paper, using the lattice Boltzmann method, pore-scale numerical studies are conducted to investigate diffusion-reaction processes in 2D hierarchical porous media generated by self-developed reconstruction scheme. Complex interactions between porous structures and reactive transport are revealed under different conditions. Simulation results show that adding macropores can greatly enhance the mass transport, but at the same time reducemore » the reactive surface, leading to complex change trend of the total reaction rate. Effects of gradient distribution of macropores within the porous medium are also investigated. It is found that a front-loose, back-tight (FLBT) hierarchical structure is desirable for enhancing mass transport, increasing total reaction rate, and improving catalyst utilization. Finally, on the whole, from the viewpoint of reducing cost and improving material performance, hierarchical porous structures, especially gradient structures with the size of macropores gradually decreasing along the transport direction, are desirable for catalyst application.« less

Pore-scale study of effects of macroscopic pores and their distributions on reactive transport in hierarchical porous media

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, Li; Zhang, Ruiyuan; Min, Ting

For applications of reactive transport in porous media, optimal porous structures should possess both high surface area for reactive sites loading and low mass transport resistance. Hierarchical porous media with a combination of pores at different scales are designed for this purpose. In this paper, using the lattice Boltzmann method, pore-scale numerical studies are conducted to investigate diffusion-reaction processes in 2D hierarchical porous media generated by self-developed reconstruction scheme. Complex interactions between porous structures and reactive transport are revealed under different conditions. Simulation results show that adding macropores can greatly enhance the mass transport, but at the same time reducemore » the reactive surface, leading to complex change trend of the total reaction rate. Effects of gradient distribution of macropores within the porous medium are also investigated. It is found that a front-loose, back-tight (FLBT) hierarchical structure is desirable for enhancing mass transport, increasing total reaction rate, and improving catalyst utilization. Finally, on the whole, from the viewpoint of reducing cost and improving material performance, hierarchical porous structures, especially gradient structures with the size of macropores gradually decreasing along the transport direction, are desirable for catalyst application.« less

Fabricatable nanopore sensors with an atomic thickness

NASA Astrophysics Data System (ADS)

Luan, Binquan; Bai, Jingwei; Stolovitzky, Gustavo

2013-10-01

When analyzing biological molecules (such as DNA and proteins) transported through a nanopore sensor, the pore length limits both the sensitivity and the spatial resolution. Atomically thin as a graphene nanopore is, it is difficult to make graphene pores and the scalable-fabrication of those pores has not yet been possible. We theoretically studied a type of atomically thin nanopores that are formed by intersection of two perpendicular nano-slits. Based on theoretical analyses, we demonstrate that slit nanopores behave similarly to graphene pores and can be manufactured at a wafer scale.

Characterization of double continuum formulations of transport through pore-scale information

NASA Astrophysics Data System (ADS)

Porta, G.; Ceriotti, G.; Bijeljic, B.

2016-12-01

Information on pore-scale characteristics is becoming increasingly available at unprecedented levels of detail from modern visualization/data-acquisition techniques. These advancements are not completely matched by corresponding developments of operational procedures according to which we can engineer theoretical findings aiming at improving our ability to reduce the uncertainty associated with the outputs of continuum-scale models to be employed at large scales. We present here a modeling approach which rests on pore-scale information to achieve a complete characterization of a double continuum model of transport and fluid-fluid reactive processes. Our model makes full use of pore-scale velocity distributions to identify mobile and immobile regions. We do so on the basis of a pointwise (in the pore space) evaluation of the relative strength of advection and diffusion time scales, as rendered by spatially variable values of local Péclet numbers. After mobile and immobile regions are demarcated, we build a simplified unit cell which is employed as a representative proxy of the real porous domain. This model geometry is then employed to simplify the computation of the effective parameters embedded in the double continuum transport model, while retaining relevant information from the pore-scale characterization of the geometry and velocity field. We document results which illustrate the applicability of the methodology to predict transport of a passive tracer within two- and three-dimensional media upon comparison with direct pore-scale numerical simulation of transport in the same geometrical settings. We also show preliminary results about the extension of this model to fluid-fluid reactive transport processes. In this context, we focus on results obtained in two-dimensional porous systems. We discuss the impact of critical quantities required as input to our modeling approach to obtain continuum-scale outputs. We identify the key limitations of the proposed methodology and discuss its capability also in comparison with alternative approaches grounded, e.g., on nonlocal and particle-based approximations.

Scaling of seismicity induced by nonlinear fluid-rock interaction after an injection stop

NASA Astrophysics Data System (ADS)

Johann, L.; Dinske, C.; Shapiro, S. A.

2016-11-01

Fluid injections into unconventional reservoirs, performed for fluid-mobility enhancement, are accompanied by microseismic activity also after the injection. Previous studies revealed that the triggering of seismic events can be effectively described by nonlinear diffusion of pore fluid pressure perturbations where the hydraulic diffusivity becomes pressure dependent. The spatiotemporal distribution of postinjection-induced microseismicity has two important features: the triggering front, corresponding to early and distant events, and the back front, representing the time-dependent spatial envelope of the growing seismic quiescence zone. Here for the first time, we describe analytically the temporal behavior of these two fronts after the injection stop in the case of nonlinear pore fluid pressure diffusion. We propose a scaling law for the fronts and show that they are sensitive to the degree of nonlinearity and to the Euclidean dimension of the dominant growth of seismicity clouds. To validate the theoretical finding, we numerically model nonlinear pore fluid pressure diffusion and generate synthetic catalogs of seismicity. Additionally, we apply the new scaling relation to several case studies of injection-induced seismicity. The derived scaling laws describe well synthetic and real data.

Developing an Effective Model for Shale Gas Flow in Nano-scale Pore Clusters based on FIB-SEM Images

NASA Astrophysics Data System (ADS)

Jiang, W. B.; Lin, M.; Yi, Z. X.; Li, H. S.

2016-12-01

Nano-scale pores existed in the form of clusters are the controlling void space in shale gas reservoir. Gas transport in nanopores which has a significant influence on shale gas' recoverability displays multiple transport regimes, including viscous, slippage flow and Knudsen diffusion. In addition, it is also influenced by pore space characteristics. For convenience and efficiency consideration, it is necessary to develop an upscaling model from nano pore to pore cluster scale. Existing models are more like framework functions that provide a format, because the parameters that represent pore space characteristics are underdetermined and may have multiple possibilities. Therefore, it is urgent to make them clear and obtained a model that is closer to reality. FIB-SEM imaging technology is able to acquire three dimensional images with nanometer resolution that nano pores can be visible. Based on the images of two shale samples, we used a high-precision pore network extraction algorithm to generate equivalent pore networks and simulate multiple regime (non-Darcy) flow in it. Several structural parameters can be obtained through pore network modelling. It is found that although the throat-radius distributions are very close, throat flux-radius distributions of different samples can be divided into two categories. The variation of tortuosity with pressure and the overall trend of throat-flux distribution changes with pressure are disclosed. A deeper understanding of shale gas flow in nano-scale pore clusters is obtained. After all, an upscaling model that connects absolute permeability, apparent permeability and other characteristic parameters is proposed, and the best parameter scheme considering throat number-radius distribution and flowing porosity for this model is selected out of three schemes based on pore scale results, and it can avoid multiple-solution problem and is useful in reservoir modelling and experiment result analysis, etc. This work is supported by the Strategic Priority Research Program of the Chinese Academy of Sciences (XDB10020302), the National Natural Science Foundation of China (41574129), the Key Instrument Developing Project of the CAS (ZDYZ2012-1-08-02), the 973 Program (2014CB239004).

Pore-scale simulation of microbial growth using a genome-scale metabolic model: Implications for Darcy-scale reactive transport

NASA Astrophysics Data System (ADS)

Tartakovsky, G. D.; Tartakovsky, A. M.; Scheibe, T. D.; Fang, Y.; Mahadevan, R.; Lovley, D. R.

2013-09-01

Recent advances in microbiology have enabled the quantitative simulation of microbial metabolism and growth based on genome-scale characterization of metabolic pathways and fluxes. We have incorporated a genome-scale metabolic model of the iron-reducing bacteria Geobacter sulfurreducens into a pore-scale simulation of microbial growth based on coupling of iron reduction to oxidation of a soluble electron donor (acetate). In our model, fluid flow and solute transport is governed by a combination of the Navier-Stokes and advection-diffusion-reaction equations. Microbial growth occurs only on the surface of soil grains where solid-phase mineral iron oxides are available. Mass fluxes of chemical species associated with microbial growth are described by the genome-scale microbial model, implemented using a constraint-based metabolic model, and provide the Robin-type boundary condition for the advection-diffusion equation at soil grain surfaces. Conventional models of microbially-mediated subsurface reactions use a lumped reaction model that does not consider individual microbial reaction pathways, and describe reactions rates using empirically-derived rate formulations such as the Monod-type kinetics. We have used our pore-scale model to explore the relationship between genome-scale metabolic models and Monod-type formulations, and to assess the manifestation of pore-scale variability (microenvironments) in terms of apparent Darcy-scale microbial reaction rates. The genome-scale model predicted lower biomass yield, and different stoichiometry for iron consumption, in comparison to prior Monod formulations based on energetics considerations. We were able to fit an equivalent Monod model, by modifying the reaction stoichiometry and biomass yield coefficient, that could effectively match results of the genome-scale simulation of microbial behaviors under excess nutrient conditions, but predictions of the fitted Monod model deviated from those of the genome-scale model under conditions in which one or more nutrients were limiting. The fitted Monod kinetic model was also applied at the Darcy scale; that is, to simulate average reaction processes at the scale of the entire pore-scale model domain. As we expected, even under excess nutrient conditions for which the Monod and genome-scale models predicted equal reaction rates at the pore scale, the Monod model over-predicted the rates of biomass growth and iron and acetate utilization when applied at the Darcy scale. This discrepancy is caused by an inherent assumption of perfect mixing over the Darcy-scale domain, which is clearly violated in the pore-scale models. These results help to explain the need to modify the flux constraint parameters in order to match observations in previous applications of the genome-scale model at larger scales. These results also motivate further investigation of quantitative multi-scale relationships between fundamental behavior at the pore scale (where genome-scale models are appropriately applied) and observed behavior at larger scales (where predictions of reactive transport phenomena are needed).

Pore-scale simulation of microbial growth using a genome-scale metabolic model: Implications for Darcy-scale reactive transport

NASA Astrophysics Data System (ADS)

Scheibe, T. D.; Tartakovsky, G.; Tartakovsky, A. M.; Fang, Y.; Mahadevan, R.; Lovley, D. R.

2012-12-01

Recent advances in microbiology have enabled the quantitative simulation of microbial metabolism and growth based on genome-scale characterization of metabolic pathways and fluxes. We have incorporated a genome-scale metabolic model of the iron-reducing bacteria Geobacter sulfurreducens into a pore-scale simulation of microbial growth based on coupling of iron reduction to oxidation of a soluble electron donor (acetate). In our model, fluid flow and solute transport is governed by a combination of the Navier-Stokes and advection-diffusion-reaction equations. Microbial growth occurs only on the surface of soil grains where solid-phase mineral iron oxides are available. Mass fluxes of chemical species associated with microbial growth are described by the genome-scale microbial model, implemented using a constraint-based metabolic model, and provide the Robin-type boundary condition for the advection-diffusion equation at soil grain surfaces. Conventional models of microbially-mediated subsurface reactions use a lumped reaction model that does not consider individual microbial reaction pathways, and describe reactions rates using empirically-derived rate formulations such as the Monod-type kinetics. We have used our pore-scale model to explore the relationship between genome-scale metabolic models and Monod-type formulations, and to assess the manifestation of pore-scale variability (microenvironments) in terms of apparent Darcy-scale microbial reaction rates. The genome-scale model predicted lower biomass yield, and different stoichiometry for iron consumption, in comparison to prior Monod formulations based on energetics considerations. We were able to fit an equivalent Monod model, by modifying the reaction stoichiometry and biomass yield coefficient, that could effectively match results of the genome-scale simulation of microbial behaviors under excess nutrient conditions, but predictions of the fitted Monod model deviated from those of the genome-scale model under conditions in which one or more nutrients were limiting. The fitted Monod kinetic model was also applied at the Darcy scale; that is, to simulate average reaction processes at the scale of the entire pore-scale model domain. As we expected, even under excess nutrient conditions for which the Monod and genome-scale models predicted equal reaction rates at the pore scale, the Monod model over-predicted the rates of biomass growth and iron and acetate utilization when applied at the Darcy scale. This discrepancy is caused by an inherent assumption of perfect mixing over the Darcy-scale domain, which is clearly violated in the pore-scale models. These results help to explain the need to modify the flux constraint parameters in order to match observations in previous applications of the genome-scale model at larger scales. These results also motivate further investigation of quantitative multi-scale relationships between fundamental behavior at the pore scale (where genome-scale models are appropriately applied) and observed behavior at larger scales (where predictions of reactive transport phenomena are needed).

Pore-scale simulation of microbial growth using a genome-scale metabolic model: Implications for Darcy-scale reactive transport

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tartakovsky, Guzel D.; Tartakovsky, Alexandre M.; Scheibe, Timothy D.

2013-09-07

Recent advances in microbiology have enabled the quantitative simulation of microbial metabolism and growth based on genome-scale characterization of metabolic pathways and fluxes. We have incorporated a genome-scale metabolic model of the iron-reducing bacteria Geobacter sulfurreducens into a pore-scale simulation of microbial growth based on coupling of iron reduction to oxidation of a soluble electron donor (acetate). In our model, fluid flow and solute transport is governed by a combination of the Navier-Stokes and advection-diffusion-reaction equations. Microbial growth occurs only on the surface of soil grains where solid-phase mineral iron oxides are available. Mass fluxes of chemical species associated withmore » microbial growth are described by the genome-scale microbial model, implemented using a constraint-based metabolic model, and provide the Robin-type boundary condition for the advection-diffusion equation at soil grain surfaces. Conventional models of microbially-mediated subsurface reactions use a lumped reaction model that does not consider individual microbial reaction pathways, and describe reactions rates using empirically-derived rate formulations such as the Monod-type kinetics. We have used our pore-scale model to explore the relationship between genome-scale metabolic models and Monod-type formulations, and to assess the manifestation of pore-scale variability (microenvironments) in terms of apparent Darcy-scale microbial reaction rates. The genome-scale model predicted lower biomass yield, and different stoichiometry for iron consumption, in comparisonto prior Monod formulations based on energetics considerations. We were able to fit an equivalent Monod model, by modifying the reaction stoichiometry and biomass yield coefficient, that could effectively match results of the genome-scale simulation of microbial behaviors under excess nutrient conditions, but predictions of the fitted Monod model deviated from those of the genome-scale model under conditions in which one or more nutrients were limiting. The fitted Monod kinetic model was also applied at the Darcy scale; that is, to simulate average reaction processes at the scale of the entire pore-scale model domain. As we expected, even under excess nutrient conditions for which the Monod and genome-scale models predicted equal reaction rates at the pore scale, the Monod model over-predicted the rates of biomass growth and iron and acetate utilization when applied at the Darcy scale. This discrepancy is caused by an inherent assumption of perfect mixing over the Darcy-scale domain, which is clearly violated in the pore-scale models. These results help to explain the need to modify the flux constraint parameters in order to match observations in previous applications of the genome-scale model at larger scales. These results also motivate further investigation of quantitative multi-scale relationships between fundamental behavior at the pore scale (where genome-scale models are appropriately applied) and observed behavior at larger scales (where predictions of reactive transport phenomena are needed).« less

Pore-scale and continuum simulations of solute transport micromodel benchmark experiments

DOE PAGES

Oostrom, M.; Mehmani, Y.; Romero-Gomez, P.; ...

2014-06-18

Four sets of nonreactive solute transport experiments were conducted with micromodels. Three experiments with one variable, i.e., flow velocity, grain diameter, pore-aspect ratio, and flow-focusing heterogeneity were in each set. The data sets were offered to pore-scale modeling groups to test their numerical simulators. Each set consisted of two learning experiments, for which our results were made available, and one challenge experiment, for which only the experimental description and base input parameters were provided. The experimental results showed a nonlinear dependence of the transverse dispersion coefficient on the Peclet number, a negligible effect of the pore-aspect ratio on transverse mixing,more » and considerably enhanced mixing due to flow focusing. Five pore-scale models and one continuum-scale model were used to simulate the experiments. Of the pore-scale models, two used a pore-network (PN) method, two others are based on a lattice Boltzmann (LB) approach, and one used a computational fluid dynamics (CFD) technique. Furthermore, we used the learning experiments, by the PN models, to modify the standard perfect mixing approach in pore bodies into approaches to simulate the observed incomplete mixing. The LB and CFD models used the learning experiments to appropriately discretize the spatial grid representations. For the continuum modeling, the required dispersivity input values were estimated based on published nonlinear relations between transverse dispersion coefficients and Peclet number. Comparisons between experimental and numerical results for the four challenge experiments show that all pore-scale models were all able to satisfactorily simulate the experiments. The continuum model underestimated the required dispersivity values, resulting in reduced dispersion. The PN models were able to complete the simulations in a few minutes, whereas the direct models, which account for the micromodel geometry and underlying flow and transport physics, needed up to several days on supercomputers to resolve the more complex problems.« less

Effects of pore-scale physics on uranium geochemistry in Hanford sediments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hu, Qinhong; Ewing, Robert P.

Overall, this work examines a key scientific issue, mass transfer limitations at the pore-scale, using both new instruments with high spatial resolution, and new conceptual and modeling paradigms. The complementary laboratory and numerical approaches connect pore-scale physics to macroscopic measurements, providing a previously elusive scale integration. This Exploratory research project produced five peer-reviewed journal publications and eleven scientific presentations. This work provides new scientific understanding, allowing the DOE to better incorporate coupled physical and chemical processes into decision making for environmental remediation and long-term stewardship.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mouzakis, Katherine M.; Navarre-Sitchler, Alexis K.; Rother, Gernot

Carbon capture, utilization, and storage, one proposed method of reducing anthropogenic emissions of CO 2, relies on low permeability formations, such as shales, above injection formations to prevent upward migration of the injected CO 2. Porosity in caprocks evaluated for sealing capacity before injection can be altered by geochemical reactions induced by dissolution of injected CO 2 into pore fluids, impacting long-term sealing capacity. Therefore, long-term performance of CO 2 sequestration sites may be dependent on both initial distribution and connectivity of pores in caprocks, and on changes induced by geochemical reaction after injection of CO 2, which are currentlymore » poorly understood. This paper presents results from an experimental study of changes to caprock porosity and pore network geometry in two caprock formations under conditions relevant to CO 2 sequestration. Pore connectivity and total porosity increased in the Gothic Shale; while total porosity increased but pore connectivity decreased in the Marine Tuscaloosa. Gothic Shale is a carbonate mudstone that contains volumetrically more carbonate minerals than Marine Tuscaloosa. Carbonate minerals dissolved to a greater extent than silicate minerals in Gothic Shale under high CO 2 conditions, leading to increased porosity at length scales <~200 nm that contributed to increased pore connectivity. In contrast, silicate minerals dissolved to a greater extent than carbonate minerals in Marine Tuscaloosa leading to increased porosity at all length scales, and specifically an increase in the number of pores >~1 μm. Mineral reactions also contributed to a decrease in pore connectivity, possibly as a result of precipitation in pore throats or hydration of the high percentage of clays. Finally, this study highlights the role that mineralogy of the caprock can play in geochemical response to CO 2 injection and resulting changes in sealing capacity in long-term CO 2 storage projects.« less

Antera 3D capabilities for pore measurements.

PubMed

Messaraa, C; Metois, A; Walsh, M; Flynn, J; Doyle, L; Robertson, N; Mansfield, A; O'Connor, C; Mavon, A

2018-04-29

The cause of enlarged pores remains obscure but still remains of concern for women. To complement subjective methods, bioengineered methods are needed for quantification of pores visibility following treatments. The study objective was to demonstrate the suitability of pore measurements from the Antera 3D. Pore measurements were collected on 22 female volunteers aged 18-65 years with the Antera 3D, the DermaTOP and image analysis on photographs. Additionally, 4 raters graded pore size on photographs on a scale 0-5. Repeatability of Antera 3D parameters was ascertained and the benefit of a pore minimizer product on the cheek was assessed on a sub panel of seven female volunteers. Pore parameters using the Antera were shown to depict pore severity similar to raters on photographs, except for Max Depth. Mean pore volume, mean pore area and count were moderately correlated with DermaTOP parameters (up to r = .50). No relationship was seen between the Antera 3D and pore visibility analysis on photographs. The most repeatable parameters were found to be mean pore volume, mean pore area and max depth, especially for the small and medium filters. The benefits of a pore minimizer product were the most striking for mean pore volume and mean pore area when using the small filter for analysis, rather than the medium/large ones. Pore measurements with the Antera 3D represent a reliable tool for efficacy and field studies, with an emphasis of the small filter for analysis for the mean pore volume/mean pore area parameters. © 2018 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.

Pore-Scale Modeling of Pore Structure Effects on P-Wave Scattering Attenuation in Dry Rocks

PubMed Central

Li, Tianyang; Qiu, Hao; Wang, Feifei

2015-01-01

Underground rocks usually have complex pore system with a variety of pore types and a wide range of pore size. The effects of pore structure on elastic wave attenuation cannot be neglected. We investigated the pore structure effects on P-wave scattering attenuation in dry rocks by pore-scale modeling based on the wave theory and the similarity principle. Our modeling results indicate that pore size, pore shape (such as aspect ratio), and pore density are important factors influencing P-wave scattering attenuation in porous rocks, and can explain the variation of scattering attenuation at the same porosity. From the perspective of scattering attenuation, porous rocks can safely suit to the long wavelength assumption when the ratio of wavelength to pore size is larger than 15. Under the long wavelength condition, the scattering attenuation coefficient increases as a power function as the pore density increases, and it increases exponentially with the increase in aspect ratio. For a certain porosity, rocks with smaller aspect ratio and/or larger pore size have stronger scattering attenuation. When the pore aspect ratio is larger than 0.5, the variation of scattering attenuation at the same porosity is dominantly caused by pore size and almost independent of the pore aspect ratio. These results lay a foundation for pore structure inversion from elastic wave responses in porous rocks. PMID:25961729

Nonaqueous Phase Liquid Dissolution in Porous Media: Multi-Scale Effects of Multi-Component Dissolution Kinetics on Cleanup Time

DOE Office of Scientific and Technical Information (OSTI.GOV)

McNab, W; Ezzedine, S; Detwiler, R

2007-02-26

Industrial organic solvents such as trichloroethylene (TCE) and tetrachloroethylene (PCE) constitute a principal class of groundwater contaminants. Cleanup of groundwater plume source areas associated with these compounds is problematic, in part, because the compounds often exist in the subsurface as dense nonaqueous phase liquids (DNAPLs). Ganglia (or 'blobs') of DNAPL serve as persistent sources of contaminants that are difficult to locate and remediate (e.g. Fenwick and Blunt, 1998). Current understanding of the physical and chemical processes associated with dissolution of DNAPLs in the subsurface is incomplete and yet is critical for evaluating long-term behavior of contaminant migration, groundwater cleanup, andmore » the efficacy of source area cleanup technologies. As such, a goal of this project has been to contribute to this critical understanding by investigating the multi-phase, multi-component physics of DNAPL dissolution using state-of-the-art experimental and computational techniques. Through this research, we have explored efficient and accurate conceptual and numerical models for source area contaminant transport that can be used to better inform the modeling of source area contaminants, including those at the LLNL Superfund sites, to re-evaluate existing remediation technologies, and to inspire or develop new remediation strategies. The problem of DNAPL dissolution in natural porous media must be viewed in the context of several scales (Khachikian and Harmon, 2000), including the microscopic level at which capillary forces, viscous forces, and gravity/buoyancy forces are manifested at the scale of individual pores (Wilson and Conrad, 1984; Chatzis et al., 1988), the mesoscale where dissolution rates are strongly influenced by the local hydrodynamics, and the field-scale. Historically, the physico-chemical processes associated with DNAPL dissolution have been addressed through the use of lumped mass transfer coefficients which attempt to quantify the dissolution rate in response to local dissolved-phase concentrations distributed across the source area using a volume-averaging approach (Figure 1). The fundamental problem with the lumped mass transfer parameter is that its value is typically derived empirically through column-scale experiments that combine the effects of pore-scale flow, diffusion, and pore-scale geometry in a manner that does not provide a robust theoretical basis for upscaling. In our view, upscaling processes from the pore-scale to the field-scale requires new computational approaches (Held and Celia, 2001) that are directly linked to experimental studies of dissolution at the pore scale. As such, our investigation has been multi-pronged, combining theory, experiments, numerical modeling, new data analysis approaches, and a synthesis of previous studies (e.g. Glass et al, 2001; Keller et al., 2002) aimed at quantifying how the mechanisms controlling dissolution at the pore-scale control the long-term dissolution of source areas at larger scales.« less

Dispersion upscaling from a pore scale characterization of Lagrangian velocities

NASA Astrophysics Data System (ADS)

Turuban, Régis; de Anna, Pietro; Jiménez-Martínez, Joaquín; Tabuteau, Hervé; Méheust, Yves; Le Borgne, Tanguy

2013-04-01

Mixing and reactive transport are primarily controlled by the interplay between diffusion, advection and reaction at pore scale. Yet, how the distribution and spatial correlation of the velocity field at pore scale impact these processes is still an open question. Here we present an experimental investigation of the distribution and correlation of pore scale velocities and its relation with upscaled dispersion. We use a quasi two-dimensional (2D) horizontal set up, consisting of two glass plates filled with cylinders representing the grains of the porous medium : the cell is built by soft lithography technique, wich allows for full control of the system geometry. The local velocity field is quantified from particle tracking velocimetry using microspheres that are advected with the pore scale flow. Their displacement is purely advective, as the particle size is chosen large enough to avoid diffusion. We thus obtain particle trajectories as well as lagrangian velocities in the entire system. The measured velocity field shows the existence of a network of preferential flow paths in channels with high velocities, as well as very low velocity in stagnation zones, with a non Gaussian distribution. Lagrangian velocities are long range correlated in time, which implies a non-fickian scaling of the longitudinal variance of particle positions. To upscale this process we develop an effective transport model, based on correlated continous time random walk, which is entirely parametrized by the pore scale velocity distribution and correlation. The model predictions are compared with conservative tracer test data for different Peclet numbers. Furthermore, we investigate the impact of different pore geometries on the distribution and correlation of Lagrangian velocities and we discuss the link between these properties and the effective dispersion behavior.

Comprehensive study of thin film evaporation from nanoporous membranes for enhanced thermal management

NASA Astrophysics Data System (ADS)

Wilke, Kyle; Barabadi, Banafsheh; Lu, Zhengmao; Zhang, Tiejun; Wang, Evelyn

Performance of emerging electronics is often dictated by the ability to dissipate heat generated in the device. Thin film evaporation from nanopores promises enhanced thermal management by reducing the thermal transport resistance across the liquid film while providing capillary pumping. We present a study of the dependence of evaporation from nanopores on a variety of geometric parameters. Anodic aluminum oxide membranes were used as an experimental template. A biphilic treatment was also used to create a hydrophobic section of the pore to control meniscus location. We demonstrated different heat transfer regimes and observed more than an order of magnitude increase in dissipated heat flux by confining fluid within the nanopore. Pore diameter had little effect on evaporation performance at pore radii of this length scale due to the negligible conduction resistance from the pore wall to the evaporating interface. The dissipated heat flux scaled linearly with porosity as the evaporative area increased. Furthermore, it was demonstrated that moving the meniscus as little as 1 μm into the pore could decrease performance significantly. The results provide a better understanding of evaporation from nanopores and provide guidance in future device design.

Hybrid discrete-continuum modeling for transport, biofilm development and solid restructuring including electrostatic effects

NASA Astrophysics Data System (ADS)

Prechtel, Alexander; Ray, Nadja; Rupp, Andreas

2017-04-01

We want to present an approach for the mathematical, mechanistic modeling and numerical treatment of processes leading to the formation, stability, and turnover of soil micro-aggregates. This aims at deterministic aggregation models including detailed mechanistic pore-scale descriptions to account for the interplay of geochemistry and microbiology, and the link to soil functions as, e.g., the porosity. We therefore consider processes at the pore scale and the mesoscale (laboratory scale). At the pore scale transport by diffusion, advection, and drift emerging from electric forces can be taken into account, in addition to homogeneous and heterogeneous reactions of species. In the context of soil micro-aggregates the growth of biofilms or other glueing substances as EPS (extracellular polymeric substances) is important and affects the structure of the pore space in space and time. This model is upscaled mathematically in the framework of (periodic) homogenization to transfer it to the mesoscale resulting in effective coefficients/parameters there. This micro-macro model thus couples macroscopic equations that describe the transport and fluid flow at the scale of the porous medium (mesoscale) with averaged time- and space-dependent coefficient functions. These functions may be explicitly computed by means of auxiliary cell problems (microscale). Finally, the pore space in which the cell problems are defined is time and space dependent and its geometry inherits information from the transport equation's solutions. The microscale problems rely on versatile combinations of cellular automata and discontiuous Galerkin methods while on the mesoscale mixed finite elements are used. The numerical simulations allow to study the interplay between these processes.

Assessing the utility of FIB-SEM images for shale digital rock physics

NASA Astrophysics Data System (ADS)

Kelly, Shaina; El-Sobky, Hesham; Torres-Verdín, Carlos; Balhoff, Matthew T.

2016-09-01

Shales and other unconventional or low permeability (tight) reservoirs house vast quantities of hydrocarbons, often demonstrate considerable water uptake, and are potential repositories for fluid sequestration. The pore-scale topology and fluid transport mechanisms within these nanoporous sedimentary rocks remain to be fully understood. Image-informed pore-scale models are useful tools for studying porous media: a debated question in shale pore-scale petrophysics is whether there is a representative elementary volume (REV) for shale models? Furthermore, if an REV exists, how does it differ among petrophysical properties? We obtain three dimensional (3D) models of the topology of microscale shale volumes from image analysis of focused ion beam-scanning electron microscope (FIB-SEM) image stacks and investigate the utility of these models as a potential REV for shale. The scope of data used in this work includes multiple local groups of neighboring FIB-SEM images of different microscale sizes, corresponding core-scale (milli- and centimeters) laboratory data, and, for comparison, series of two-dimensional (2D) cross sections from broad ion beam SEM images (BIB-SEM), which capture a larger microscale field of view than the FIB-SEM images; this array of data is larger than the majority of investigations with FIB-SEM-derived microscale models of shale. Properties such as porosity, organic matter content, and pore connectivity are extracted from each model. Assessments of permeability with single phase, pressure-driven flow simulations are performed in the connected pore space of the models using the lattice-Boltzmann method. Calculated petrophysical properties are compared to those of neighboring FIB-SEM images and to core-scale measurements of the sample associated with the FIB-SEM sites. Results indicate that FIB-SEM images below ∼5000 μm3 volume (the largest volume analyzed) are not a suitable REV for shale permeability and pore-scale networks; i.e. field of view is compromised at the expense of detailed, but often unconnected, nanopore morphology. Further, we find that it is necessary to acquire several local FIB-SEM or BIB-SEM images and correlate their extracted geometric properties to improve the likelihood of achieving representative values of porosity and organic matter volume. Our work indicates that FIB-SEM images of microscale volumes of shale are a qualitative tool for petrophysical and transport analysis. Finally, we offer alternatives for quantitative pore-scale assessments of shale.

Evaluating the hydraulic and transport properties of peat soil using pore network modeling and X-ray micro computed tomography

NASA Astrophysics Data System (ADS)

Gharedaghloo, Behrad; Price, Jonathan S.; Rezanezhad, Fereidoun; Quinton, William L.

2018-06-01

Micro-scale properties of peat pore space and their influence on hydraulic and transport properties of peat soils have been given little attention so far. Characterizing the variation of these properties in a peat profile can increase our knowledge on the processes controlling contaminant transport through peatlands. As opposed to the common macro-scale (or bulk) representation of groundwater flow and transport processes, a pore network model (PNM) simulates flow and transport processes within individual pores. Here, a pore network modeling code capable of simulating advective and diffusive transport processes through a 3D unstructured pore network was developed; its predictive performance was evaluated by comparing its results to empirical values and to the results of computational fluid dynamics (CFD) simulations. This is the first time that peat pore networks have been extracted from X-ray micro-computed tomography (μCT) images of peat deposits and peat pore characteristics evaluated in a 3D approach. Water flow and solute transport were modeled in the unstructured pore networks mapped directly from μCT images. The modeling results were processed to determine the bulk properties of peat deposits. Results portray the commonly observed decrease in hydraulic conductivity with depth, which was attributed to the reduction of pore radius and increase in pore tortuosity. The increase in pore tortuosity with depth was associated with more decomposed peat soil and decreasing pore coordination number with depth, which extended the flow path of fluid particles. Results also revealed that hydraulic conductivity is isotropic locally, but becomes anisotropic after upscaling to core-scale; this suggests the anisotropy of peat hydraulic conductivity observed in core-scale and field-scale is due to the strong heterogeneity in the vertical dimension that is imposed by the layered structure of peat soils. Transport simulations revealed that for a given solute, the effective diffusion coefficient decreases with depth due to the corresponding increase of diffusional tortuosity. Longitudinal dispersivity of peat also was computed by analyzing advective-dominant transport simulations that showed peat dispersivity is similar to the empirical values reported in the same peat soil; it is not sensitive to soil depth and does not vary much along the soil profile.

Preferential flow from pore to landscape scales

NASA Astrophysics Data System (ADS)

Koestel, J. K.; Jarvis, N.; Larsbo, M.

2017-12-01

In this presentation, we give a brief personal overview of some recent progress in quantifying preferential flow in the vadose zone, based on our own work and those of other researchers. One key challenge is to bridge the gap between the scales at which preferential flow occurs (i.e. pore to Darcy scales) and the scales of interest for management (i.e. fields, catchments, regions). We present results of recent studies that exemplify the potential of 3-D non-invasive imaging techniques to visualize and quantify flow processes at the pore scale. These studies should lead to a better understanding of how the topology of macropore networks control key state variables like matric potential and thus the strength of preferential flow under variable initial and boundary conditions. Extrapolation of this process knowledge to larger scales will remain difficult, since measurement technologies to quantify macropore networks at these larger scales are lacking. Recent work suggests that the application of key concepts from percolation theory could be useful in this context. Investigation of the larger Darcy-scale heterogeneities that generate preferential flow patterns at the soil profile, hillslope and field scales has been facilitated by hydro-geophysical measurement techniques that produce highly spatially and temporally resolved data. At larger regional and global scales, improved methods of data-mining and analyses of large datasets (machine learning) may help to parameterize models as well as lead to new insights into the relationships between soil susceptibility to preferential flow and site attributes (climate, land uses, soil types).

A Generalized Hybrid Multiscale Modeling Approach for Flow and Reactive Transport in Porous Media

NASA Astrophysics Data System (ADS)

Yang, X.; Meng, X.; Tang, Y. H.; Guo, Z.; Karniadakis, G. E.

2017-12-01

Using emerging understanding of biological and environmental processes at fundamental scales to advance predictions of the larger system behavior requires the development of multiscale approaches, and there is strong interest in coupling models at different scales together in a hybrid multiscale simulation framework. A limited number of hybrid multiscale simulation methods have been developed for subsurface applications, mostly using application-specific approaches for model coupling. The proposed generalized hybrid multiscale approach is designed with minimal intrusiveness to the at-scale simulators (pre-selected) and provides a set of lightweight C++ scripts to manage a complex multiscale workflow utilizing a concurrent coupling approach. The workflow includes at-scale simulators (using the lattice-Boltzmann method, LBM, at the pore and Darcy scale, respectively), scripts for boundary treatment (coupling and kriging), and a multiscale universal interface (MUI) for data exchange. The current study aims to apply the generalized hybrid multiscale modeling approach to couple pore- and Darcy-scale models for flow and mixing-controlled reaction with precipitation/dissolution in heterogeneous porous media. The model domain is packed heterogeneously that the mixing front geometry is more complex and not known a priori. To address those challenges, the generalized hybrid multiscale modeling approach is further developed to 1) adaptively define the locations of pore-scale subdomains, 2) provide a suite of physical boundary coupling schemes and 3) consider the dynamic change of the pore structures due to mineral precipitation/dissolution. The results are validated and evaluated by comparing with single-scale simulations in terms of velocities, reactive concentrations and computing cost.

Pore scale investigation of salt precipitation inside drying porous media resolved by 4D X-ray Microscopy Imaging

NASA Astrophysics Data System (ADS)

Norouzi Rad, M.

2016-12-01

Precipitation and deposition of salts in porous media is important in many natural processes as well as industrial and environmental applications since it can modify the structure and transport properties of porous media. In the presence of soluble salt in water during evaporation from porous media, salt is transported by convection induced by capillary liquid flow toward the evaporating surface where it accumulates, whereas diffusion tends to spread the salt and homogenize concentrations in space. Therefore, the competition between the convection and diffusion (characterized by Peclet number) affects the dynamics of salt distribution in porous media. As shown in previous studies (1-3) salt crust thickness and its coverage on the surface are highly influenced by the pore size distribution on the surface and active evaporation spots. In the current study, we focus on the precipitation dynamics and pattern during diffusion-driven evaporation period (the so-called stage-2 of evaporation) when the surface is dried and vaporization plane moves below the surface. Therefore, precipitation occurs inside the porous media during this period. To investigate the details of this process, 4D X-ray Microscopy was utilized. To do so, a packed bed of silica sand was saturated with 4 Molal NaCl solution and X-ray Microscopy was used to image the sample at well-defined time intervals during the evaporation process to provide pore scale information on evaporation and precipitation dynamics. The resulted 3-D pore-scale images were segmented to quantify the evaporative water losses and the dynamics and patterns of salt precipitation inside porous media with particular focus on the characterization of the processes occurring during stage-2 evaporation affecting the precipitation dynamics. [1] Norouzi Rad, M., N. Shokri, A. Keshmiri, P. Withers (2015), Effects of grain and pore size on salt precipitation during evaporation from porous media: A pore-scale investigation, Trans. Porous. Med., 110(2), 281-294. [2] Norouzi Rad, M., N. Shokri (2014), Effects of grain angularity on NaCl precipitation in porous media during evaporation, Water Resour. Res., 50, 9020-9030. [3] Norouzi Rad, M., N. Shokri, M. Sahimi (2013), Pore-Scale Dynamics of Salt Precipitation in Drying Porous Media, Phys. Rev. E, 88, 032404.

Flow regimes during immiscible displacement

DOE Office of Scientific and Technical Information (OSTI.GOV)

Armstrong, Ryan T.; Mcclure, James; Berrill, Mark A.

Fractional ow of immiscible phases occurs at the pore scale where grain surfaces and phases interfaces obstruct phase mobility. However, the larger scale behavior is described by a saturation-dependent phenomenological relationship called relative permeability. As a consequence, pore-scale parameters, such as phase topology and/ or geometry, and details of the flow regime cannot be directly related to Darcy-scale flow parameters. It is well understood that relative permeability is not a unique relationship of wetting-phase saturation and rather depends on the experimental conditions at which it is measured. Herein we use fast X-ray microcomputed tomography to image pore-scale phase arrangements duringmore » fractional flow and then forward simulate the flow regimes using the lattice-Boltzmann method to better understand the underlying pore-scale flow regimes and their influence on Darcy-scale parameters. We find that relative permeability is highly dependent on capillary number and that the Corey model fits the observed trends. At the pore scale, while phase topologies are continuously changing on the scale of individual pores, the Euler characteristic of the nonwetting phase (NWP) averaged over a sufficiently large field of view can describe the bulk topological characteristics; the Euler characteristic decreases with increasing capillary number resulting in an increase in relative permeability. Lastly, we quantify the fraction of NWP that flows through disconnected ganglion dynamics and demonstrate that this can be a significant fraction of the NWP flux for intermediate wetting-phase saturation. Furthermore, rate dependencies occur in our homogenous sample (without capillary end effect) and the underlying cause is attributed to ganglion flow that can significantly influence phase topology during the fractional flow of immiscible phases.« less

Flow regimes during immiscible displacement

DOE PAGES

Armstrong, Ryan T.; Mcclure, James; Berrill, Mark A.; ...

2017-02-01

Fractional ow of immiscible phases occurs at the pore scale where grain surfaces and phases interfaces obstruct phase mobility. However, the larger scale behavior is described by a saturation-dependent phenomenological relationship called relative permeability. As a consequence, pore-scale parameters, such as phase topology and/ or geometry, and details of the flow regime cannot be directly related to Darcy-scale flow parameters. It is well understood that relative permeability is not a unique relationship of wetting-phase saturation and rather depends on the experimental conditions at which it is measured. Herein we use fast X-ray microcomputed tomography to image pore-scale phase arrangements duringmore » fractional flow and then forward simulate the flow regimes using the lattice-Boltzmann method to better understand the underlying pore-scale flow regimes and their influence on Darcy-scale parameters. We find that relative permeability is highly dependent on capillary number and that the Corey model fits the observed trends. At the pore scale, while phase topologies are continuously changing on the scale of individual pores, the Euler characteristic of the nonwetting phase (NWP) averaged over a sufficiently large field of view can describe the bulk topological characteristics; the Euler characteristic decreases with increasing capillary number resulting in an increase in relative permeability. Lastly, we quantify the fraction of NWP that flows through disconnected ganglion dynamics and demonstrate that this can be a significant fraction of the NWP flux for intermediate wetting-phase saturation. Furthermore, rate dependencies occur in our homogenous sample (without capillary end effect) and the underlying cause is attributed to ganglion flow that can significantly influence phase topology during the fractional flow of immiscible phases.« less

Tracer counterpermeation analysis of diffusivity in finite-length nanopores with and without single-file dynamics

DOE PAGES

Ackerman, David M.; Evans, James W.

2017-01-19

Here, we perform a tracer counterpermeation (TCP) analysis for a stochastic model of diffusive transport through a narrow linear pore where passing of species within the pore is inhibited or even excluded (single-file diffusion). TCP involves differently labeled but otherwise identical particles from two decoupled infinite reservoirs adsorbing into opposite ends of the pore, and desorbing from either end. In addition to transient behavior, we assess steady-state concentration profiles, spatial correlations, particle number fluctuations, and diffusion fluxes through the pore. From the profiles and fluxes, we determine a generalized tracer diffusion coefficient D tr(x), at various positions x within themore » pore. D tr(x) has a plateau value in the pore center scaling inversely with the pore length, but it is enhanced near the pore openings. The latter feature reflects the effect of fluctuations in adsorption and desorption, and it is also associated with a nontrivial scaling of the concentration profiles near the pore openings.« less

Tracer counterpermeation analysis of diffusivity in finite-length nanopores with and without single-file dynamics

NASA Astrophysics Data System (ADS)

Ackerman, David M.; Evans, James W.

2017-01-01

We perform a tracer counterpermeation (TCP) analysis for a stochastic model of diffusive transport through a narrow linear pore where passing of species within the pore is inhibited or even excluded (single-file diffusion). TCP involves differently labeled but otherwise identical particles from two decoupled infinite reservoirs adsorbing into opposite ends of the pore, and desorbing from either end. In addition to transient behavior, we assess steady-state concentration profiles, spatial correlations, particle number fluctuations, and diffusion fluxes through the pore. From the profiles and fluxes, we determine a generalized tracer diffusion coefficient Dtr(x ) , at various positions x within the pore. Dtr(x ) has a plateau value in the pore center scaling inversely with the pore length, but it is enhanced near the pore openings. The latter feature reflects the effect of fluctuations in adsorption and desorption, and it is also associated with a nontrivial scaling of the concentration profiles near the pore openings.

Spatial and temporal distribution of pore gas concentrations during mainstream large-scale trough composting in China.

PubMed

Zeng, Jianfei; Shen, Xiuli; Sun, Xiaoxi; Liu, Ning; Han, Lujia; Huang, Guangqun

2018-05-01

With the advantages of high treatment capacity and low operational cost, large-scale trough composting has become one of the mainstream composting patterns in composting plants in China. This study measured concentrations of O 2 , CO 2 , CH 4 and NH 3 on-site to investigate the spatial and temporal distribution of pore gas concentrations during mainstream large-scale trough composting in China. The results showed that the temperature in the center of the pile was obviously higher than that in the side of the pile. Pore O 2 concentration rapidly decreased and maintained <5% (in volume) for 38 days or more in both the center and side of the pile and effective O 2 diffusion occurred at most in every two contiguous layers. Pore CO 2 and CH 4 concentrations at each measurement point were positively correlated (0.436 ≤ r ≤ 0.570, P < 0.01) and the concentrations in the side of the pile were obviously lower than those in the center. The top layer exhibited highest pore O 2 concentration and lowest CO 2 and CH 4 concentrations, and the bottom layer was on the contrary. No significant differences in pore NH 3 concentrations between different layers or between different measurement points in the same layer were found. Therefore, mixing the center and the side of the pile when mechanical turning and adjusting the height of the pile according to the physical properties of bulking agents are suggested to optimize the oxygen distribution and promote the composting process during large-scale trough composting when the pile was naturally aerated, which will contribute to improving the current undesirable atmosphere environment in China. Copyright © 2018 Elsevier Ltd. All rights reserved.

Integrating SANS and fluid-invasion methods to characterize pore structure of typical American shale oil reservoirs.

PubMed

Zhao, Jianhua; Jin, Zhijun; Hu, Qinhong; Jin, Zhenkui; Barber, Troy J; Zhang, Yuxiang; Bleuel, Markus

2017-11-13

An integration of small-angle neutron scattering (SANS), low-pressure N 2 physisorption (LPNP), and mercury injection capillary pressure (MICP) methods was employed to study the pore structure of four oil shale samples from leading Niobrara, Wolfcamp, Bakken, and Utica Formations in USA. Porosity values obtained from SANS are higher than those from two fluid-invasion methods, due to the ability of neutrons to probe pore spaces inaccessible to N 2 and mercury. However, SANS and LPNP methods exhibit a similar pore-size distribution, and both methods (in measuring total pore volume) show different results of porosity and pore-size distribution obtained from the MICP method (quantifying pore throats). Multi-scale (five pore-diameter intervals) inaccessible porosity to N 2 was determined using SANS and LPNP data. Overall, a large value of inaccessible porosity occurs at pore diameters <10 nm, which we attribute to low connectivity of organic matter-hosted and clay-associated pores in these shales. While each method probes a unique aspect of complex pore structure of shale, the discrepancy between pore structure results from different methods is explained with respect to their difference in measurable ranges of pore diameter, pore space, pore type, sample size and associated pore connectivity, as well as theoretical base and interpretation.

Nanoscale Pore Imaging and Pore Scale Fluid Flow Modeling in Chalk

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tomutsa, Liviu; Silin, Dmitriy

2004-08-19

For many rocks of high economic interest such as chalk, diatomite, tight gas sands or coal, nanometer scale resolution is needed to resolve the 3D-pore structure, which controls the flow and trapping of fluids in the rocks. Such resolutions cannot be achieved with existing tomographic technologies. A new 3D imaging method, based on serial sectioning and using the Focused Ion Beam (FIB) technology has been developed. FIB allows for the milling of layers as thin as 10 nanometers by using accelerated Ga+ ions to sputter atoms from the sample surface. After each milling step, as a new surface is exposed,more » a 2D image of this surface is generated. Next, the 2D images are stacked to reconstruct the 3D pore or grain structure. Resolutions as high as 10 nm are achievable using such a technique. A new robust method of pore-scale fluid flow modeling has been developed and applied to sandstone and chalk samples. The method uses direct morphological analysis of the pore space to characterize the petrophysical properties of diverse formations. Not only petrophysical properties (porosity, permeability, relative permeability and capillary pressures) can be computed but also flow processes, such as those encountered in various IOR approaches, can be simulated. Petrophysical properties computed with the new method using the new FIB data will be presented. Present study is a part of the development of an Electronic Core Laboratory at LBNL/UCB.« less

The Impact of the Flow Field Heterogeneity and of the Injection Rate on the Effective Reaction Rates in Carbonates: a Study at the Pore Scale

NASA Astrophysics Data System (ADS)

Nunes, J. P. P.; Bijeljic, B.; Blunt, M. J.

2015-12-01

Carbonate rocks are notoriously difficult to characterize. Their abrupt facies variations give rise to drastic changes in the petrophysical properties of the reservoir. Such heterogeneity, when further associated with variations in rock mineralogy due to diagenetic processes, result in a challenging scenario to model from the pore to the field scale. Micro-CT imaging is one of the most promising technologies to characterize porous rocks. The understanding at the pore scale of reactive and non-reactive transport is being pushed forward by recent developments in both imaging capability - 3D images with resolution of a few microns - and in modeling techniques - flow simulations in giga-cell models. We will present a particle-based method capable of predicting the evolution of petrophysical properties of carbonate cores subjected to CO2 injection at reservoir conditions (i.e. high pressures and temperatures). Reactive flow is simulated directly on the voxels of high resolution micro-CT images of rocks. Reactants are tracked using a semi-analytical streamline tracing algorithm and rock-fluid interaction is controlled by the diffusive flux of particles from the pores to the grains. We study the impact of the flow field heterogeneity and of the injection rate on the sample-averaged (i.e. effective) reaction rate of calcite dissolution in three rocks of increasing complexity: a beadpack, an oolitic limestone and a bioclastic limestone. We show how decreases in the overall dissolution rate depend on both the complexity of the pore space and also on the flow rate. This occurs even in chemically homogenous rocks. Our results suggest that the large differences observed between laboratory and field scale rates could, in part, be explained by the inhomogeneity in the flow field at the pore scale and the consequent transport-limited flux of reactants at the solid surface. Our results give valuable insight into the processes governing carbonate dissolution and provide a starting point to the refinement of upscaling techniques for reactive flows. Potential impacts for reservoir development and monitoring will also be discussed.

Effects of the soil pore network architecture on the soil's physical functionalities

NASA Astrophysics Data System (ADS)

Smet, Sarah; Beckers, Eléonore; Léonard, Angélique; Degré, Aurore

2017-04-01

The soil fluid movement's prediction is of major interest within an agricultural or environmental scope because many processes depend ultimately on the soil fluids dynamic. It is common knowledge that the soil microscopic pore network structure governs the inner-soil convective fluids flow. There isn't, however, a general methodthat consider the pore network structure as a variable in the prediction of thecore scale soil's physical functionalities. There are various possible representations of the microscopic pore network: sample scale averaged structural parameters, extrapolation of theoretic pore network, or use of all the information available by modeling within the observed pore network. Different representations implydifferent analyzing methodologies. To our knowledge, few studies have compared the micro-and macroscopic soil's characteristics for the same soil core sample. The objective of our study is to explore the relationship between macroscopic physical properties and microscopic pore network structure. The saturated hydraulic conductivity, the air permeability, the retention curve, and others classical physical parameters were measured for ten soil samples from an agricultural field. The pore network characteristics were quantified through the analyses of X-ray micro-computed tomographic images(micro-CT system Skyscan-1172) with a voxel size of 22 µm3. Some of the first results confirmed what others studies had reported. Then, the comparison between macroscopic properties and microscopic parameters suggested that the air movements depended mostly on the pore connectivity and tortuosity than on the total porosity volume. We have also found that the fractal dimension calculated from the X-ray images and the fractal dimension calculated from the retention curve were significantly different. Our communication will detailthose results and discuss the methodology: would the results be similar with a different voxel size? What are the calculated and measured parameters uncertainties? Sarah Smet, as a research fellow, acknowledges the support of the National Fund for Scientific Research (Brussels, Belgium).

Motion of Fullerenes around Topological Defects on Metals: Implications for the Progress of Molecular Scale Devices.

PubMed

Nirmalraj, Peter; Daly, Ronan; Martin, Nazario; Thompson, Damien

2017-03-08

Research on motion of molecules in the presence of thermal noise is central for progress in two-terminal molecular scale electronic devices. However, it is still unclear what influence imperfections in bottom metal electrode surface can have on molecular motion. Here, we report a two-layer crowding study, detailing the early stages of surface motion of fullerene molecules on Au(111) with nanoscale pores in a n-tetradecane chemical environment. The motion of the fullerenes is directed by crowding of the underlying n-tetradecane molecules around the pore fringes at the liquid-solid interface. We observe in real-space the growth of molecular populations around different pore geometries. Supported by atomic-scale modeling, our findings extend the established picture of molecular crowding by revealing that trapped solvent molecules serve as prime nucleation sites at nanopore fringes.

Evidence for Enhanced Matrix Diffusion in Geological Environment

NASA Astrophysics Data System (ADS)

Sato, Kiminori; Fujimoto, Koichiro; Nakata, Masataka; Shikazono, Naotatsu

2013-01-01

Molecular diffusion in rock matrix, called as matrix diffusion, has been appreciated as a static process for elemental migration in geological environment that has been acknowledged in the context of geological disposal of radioactive waste. However, incomprehensible enhancement of matrix diffusion has been reported at a number of field test sites. Here, the matrix diffusion of saline water at Horonobe, Hokkaido, Japan is highlighted directly probing angstrom-scale pores on a field scale up to 1 km by positron--positronium annihilation spectroscopy. The first application of positron--positronium annihilation spectroscopy to field-scale geophysical research reveals the slight variation of angstrom-scale pores influenced by saline water diffusion with complete accuracy. We found widely interconnected 3 Å pores, which offer the pathway of saline water diffusion with the highly enhanced effective matrix diffusion coefficient of 4× 10-6 cm2 s-1. The present findings provide unambiguous evidence that the angstrom-scale pores enhance effective matrix diffusion on a field scale in geological environment.

Statistical scaling of pore-scale Lagrangian velocities in natural porous media.

PubMed

Siena, M; Guadagnini, A; Riva, M; Bijeljic, B; Pereira Nunes, J P; Blunt, M J

2014-08-01

We investigate the scaling behavior of sample statistics of pore-scale Lagrangian velocities in two different rock samples, Bentheimer sandstone and Estaillades limestone. The samples are imaged using x-ray computer tomography with micron-scale resolution. The scaling analysis relies on the study of the way qth-order sample structure functions (statistical moments of order q of absolute increments) of Lagrangian velocities depend on separation distances, or lags, traveled along the mean flow direction. In the sandstone block, sample structure functions of all orders exhibit a power-law scaling within a clearly identifiable intermediate range of lags. Sample structure functions associated with the limestone block display two diverse power-law regimes, which we infer to be related to two overlapping spatially correlated structures. In both rocks and for all orders q, we observe linear relationships between logarithmic structure functions of successive orders at all lags (a phenomenon that is typically known as extended power scaling, or extended self-similarity). The scaling behavior of Lagrangian velocities is compared with the one exhibited by porosity and specific surface area, which constitute two key pore-scale geometric observables. The statistical scaling of the local velocity field reflects the behavior of these geometric observables, with the occurrence of power-law-scaling regimes within the same range of lags for sample structure functions of Lagrangian velocity, porosity, and specific surface area.

Laser powder-bed fusion additive manufacturing: Physics of complex melt flow and formation mechanisms of pores, spatter, and denudation zones

DOE Office of Scientific and Technical Information (OSTI.GOV)

Khairallah, Saad A.; Anderson, Andrew T.; Rubenchik, Alexander

Our study demonstrates the significant effect of the recoil pressure and Marangoni convection in laser powder bed fusion (L-PBF) of 316L stainless steel. A three-dimensional high fidelity powder-scale model reveals how the strong dynamical melt flow generates pore defects, material spattering (sparking), and denudation zones. The melt track is divided into three sections: a topological depression, a transition and a tail region, each being the location of specific physical effects. The inclusion of laser ray-tracing energy deposition in the powder-scale model improves over traditional volumetric energy deposition. It enables partial particle melting, which impacts pore defects in the denudation zone.more » Different pore formation mechanisms are observed at the edge of a scan track, at the melt pool bottom (during collapse of the pool depression), and at the end of the melt track (during laser power ramp down). Finally, we discuss remedies to these undesirable pores are discussed. The results are validated against the experiments and the sensitivity to laser absorptivity.« less

Laser powder-bed fusion additive manufacturing: Physics of complex melt flow and formation mechanisms of pores, spatter, and denudation zones

DOE PAGES

Khairallah, Saad A.; Anderson, Andrew T.; Rubenchik, Alexander; ...

2016-02-23

Our study demonstrates the significant effect of the recoil pressure and Marangoni convection in laser powder bed fusion (L-PBF) of 316L stainless steel. A three-dimensional high fidelity powder-scale model reveals how the strong dynamical melt flow generates pore defects, material spattering (sparking), and denudation zones. The melt track is divided into three sections: a topological depression, a transition and a tail region, each being the location of specific physical effects. The inclusion of laser ray-tracing energy deposition in the powder-scale model improves over traditional volumetric energy deposition. It enables partial particle melting, which impacts pore defects in the denudation zone.more » Different pore formation mechanisms are observed at the edge of a scan track, at the melt pool bottom (during collapse of the pool depression), and at the end of the melt track (during laser power ramp down). Finally, we discuss remedies to these undesirable pores are discussed. The results are validated against the experiments and the sensitivity to laser absorptivity.« less

Pore-scale modeling of Capillary Penetration of Wetting Liquid into 3D Fibrous Media: A Critical Examination of Equivalent Capillary Concept

NASA Astrophysics Data System (ADS)

Palakurthi, Nikhil Kumar; Ghia, Urmila; Comer, Ken

2013-11-01

Capillary penetration of liquid through fibrous porous media is important in many applications such as printing, drug delivery patches, sanitary wipes, and performance fabrics. Historically, capillary transport (with a distinct liquid propagating front) in porous media is modeled using capillary-bundle theory. However, it is not clear if the capillary model (Washburn equation) describes the fluid transport in porous media accurately, as it assumes uniformity of pore sizes in the porous medium. The present work investigates the limitations of the applicability of the capillary model by studying liquid penetration through virtual fibrous media with uniform and non-uniform pore-sizes. For the non-uniform-pore fibrous medium, the effective capillary radius of the fibrous medium was estimated from the pore-size distribution curve. Liquid penetration into the 3D virtual fibrous medium at micro-scale was simulated using OpenFOAM, and the numerical results were compared with the Washburn-equation capillary-model predictions. Preliminary results show that the Washburn equation over-predicts the height rise in the early stages (purely inertial and visco-inertial stages) of capillary transport.

A Moisture Function of Soil Heterotrophic Respiration Derived from Pore-scale Mechanisms

NASA Astrophysics Data System (ADS)

Yan, Z.; Todd-Brown, K. E.; Bond-Lamberty, B. P.; Bailey, V.; Liu, C.

2017-12-01

Soil heterotrophic respiration (HR) is an important process controlling carbon (C) flux, but its response to changes in soil water content (θ) is poorly understood. Earth system models (ESMs) use empirical moisture functions developed from specific sites to describe the HR-θ relationship in soils, introducing significant uncertainty. Generalized models derived from mechanisms that control substrate availability and microbial respiration are thus urgently needed. Here we derive, present, and test a novel moisture function fp developed from pore-scale mechanisms. This fp encapsulates primary physicochemical and biological processes controlling HR response to moisture variation in soils. We tested fp against a wide range of published data for different soil types, and found that fp reliably predicted diverse HR- relationships. The mathematical relationship between the parameters in fp and macroscopic soil properties such as porosity and organic C content was also established, enabling to estimate fp using soil properties. Compared with empirical moisture functions used in ESMs, this derived fp could reduce uncertainty in predicting the response of soil organic C stock to climate changes. In addition, this work is one of the first studies to upscale a mechanistic soil HR model based on pore-scale processes, thus linking the pore-scale mechanisms with macroscale observations.

Three-dimensional imaging of porous media using confocal laser scanning microscopy.

PubMed

Shah, S M; Crawshaw, J P; Boek, E S

2017-02-01

In the last decade, imaging techniques capable of reconstructing three-dimensional (3-D) pore-scale model have played a pivotal role in the study of fluid flow through complex porous media. In this study, we present advances in the application of confocal laser scanning microscopy (CLSM) to image, reconstruct and characterize complex porous geological materials with hydrocarbon reservoir and CO 2 storage potential. CLSM has a unique capability of producing 3-D thin optical sections of a material, with a wide field of view and submicron resolution in the lateral and axial planes. However, CLSM is limited in the depth (z-dimension) that can be imaged in porous materials. In this study, we introduce a 'grind and slice' technique to overcome this limitation. We discuss the practical and technical aspects of the confocal imaging technique with application to complex rock samples including Mt. Gambier and Ketton carbonates. We then describe the complete workflow of image processing to filtering and segmenting the raw 3-D confocal volumetric data into pores and grains. Finally, we use the resulting 3-D pore-scale binarized confocal data obtained to quantitatively determine petrophysical pore-scale properties such as total porosity, macro- and microporosity and single-phase permeability using lattice Boltzmann (LB) simulations, validated by experiments. © 2016 The Authors Journal of Microscopy © 2016 Royal Microscopical Society.

4D XMT of Reaction in Carbonates: Reactive Transport Dynamics at Multiples Scales

NASA Astrophysics Data System (ADS)

Menke, H. P.; Reynolds, C. A.; Andrew, M. G.; Nunes, J. P. P.; Bijeljic, B.; Blunt, M. J.

2016-12-01

Upscaling pore scale rock-fluid interaction processes for predictive modelling poses a challenge to underground carbon storage. We have completed experiments and flow modelling to investigate the impact of pore-space heterogeneity and scale on the dissolution of two limestones at both the mm and cm scales. Two samples were reacted with reservoir condition CO2-saturated brine at both scales and scanned dynamically as dissolution took place. First, 1-cm long 4-mm diameter micro cores were scanned during reactive flow at a 4-μm resolution between 4 and 40 times using 4D X-ray micro-tomography over the course of 1.5 hours using a laboratory μ-CT. Second, 3.8-cm diameter, 8-cm long macro cores were reacted at the same conditions inside a reservoir condition flow rig and imaged using a medical CT scanner. Each sample was imaged 10 times over the course of 1.5 hours at a 250 x 250 x 500-μm resolution. The reacted macro cores were then scanned inside a μ-CT at a 27-μm resolution to assess the alteration in pore-scale reaction-induced heterogeneity. It was found that both limestones showed channel formation at the pore-scale and progressive high porosity pathway dissolution at the core-scale with the more heterogeneous rock having dissolution progressing along direction of flow more quickly. Additionally, upon analysis of the high-resolution macro core images it was found that the dissolution pathways contained a distinct microstructure that was not visible at the resolution of the medical CT, where the reactive fluid had not completely dissolved the internal pore-structure. Flow was modelled in connected pathways, the flow streamlines were traced and streamline density for each voxel was calculated. It was found that the streamline density was highest in the most well-connected pathways and that density increased with increasing heterogeneity as the number of connected pathways decreased and flow was consolidated along fewer pathways. This work represents the first study of scale dependency using reservoir condition 4D X-ray tomography and provides insight into the mechanisms that control local reaction rates at multiple scales.

Pore-Scale Determination of Gas Relative Permeability in Hydrate-Bearing Sediments Using X-Ray Computed Micro-Tomography and Lattice Boltzmann Method

NASA Astrophysics Data System (ADS)

Chen, Xiongyu; Verma, Rahul; Espinoza, D. Nicolas; Prodanović, Maša.

2018-01-01

This work uses X-ray computed micro-tomography (μCT) to monitor xenon hydrate growth in a sandpack under the excess gas condition. The μCT images give pore-scale hydrate distribution and pore habit in space and time. We use the lattice Boltzmann method to calculate gas relative permeability (krg) as a function of hydrate saturation (Shyd) in the pore structure of the experimental hydrate-bearing sand retrieved from μCT data. The results suggest the krg - Shyd data fit well a new model krg = (1-Shyd)·exp(-4.95·Shyd) rather than the simple Corey model. In addition, we calculate krg-Shyd curves using digital models of hydrate-bearing sand based on idealized grain-attaching, coarse pore-filling, and dispersed pore-filling hydrate habits. Our pore-scale measurements and modeling show that the krg-Shyd curves are similar regardless of whether hydrate crystals develop grain-attaching or coarse pore-filling habits. The dispersed pore filling habit exhibits much lower gas relative permeability than the other two, but it is not observed in the experiment and not compatible with Ostwald ripening mechanisms. We find that a single grain-shape factor can be used in the Carman-Kozeny equation to calculate krg-Shyd data with known porosity and average grain diameter, suggesting it is a useful model for hydrate-bearing sand.

Multi-Scale Multi-Physics Modeling of Matrix Transport Properties in Fractured Shale Reservoirs

NASA Astrophysics Data System (ADS)

Mehmani, A.; Prodanovic, M.

2014-12-01

Understanding the shale matrix flow behavior is imperative in successful reservoir development for hydrocarbon production and carbon storage. Without a predictive model, significant uncertainties in flowback from the formation, the communication between the fracture and matrix as well as proper fracturing practice will ensue. Informed by SEM images, we develop deterministic network models that couple pores from multiple scales and their respective fluid physics. The models are used to investigate sorption hysteresis as an affordable way of inferring the nanoscale pore structure in core scale. In addition, restricted diffusion as a function of pore shape, pore-throat size ratios and network connectivity is computed to make correct interpretation of the 2D NMR maps possible. Our novel pore network models have the ability to match sorption hysteresis measurements without any tuning parameters. The results clarify a common misconception of linking type 3 nitrogen hysteresis curves to only the shale pore shape and show promising sensitivty for nanopore structre inference in core scale. The results on restricted diffusion shed light on the importance of including shape factors in 2D NMR interpretations. A priori "weighting factors" as a function of pore-throat and throat-length ratio are presented and the effect of network connectivity on diffusion is quantitatively assessed. We are currently working on verifying our models with experimental data gathered from the Eagleford formation.

Characterization and Quantification of the Pore Structures of the Shale Oil Reservoir Formations in Multiscale

NASA Astrophysics Data System (ADS)

Liu, K.; Ostadhassan, M.

2016-12-01

Due to the fast development of hydraulic fracturing and horizontal drilling, shale formations now are one important resource of energy in North America. Characterizing the pore structure of these shale formations is of critical importance in understanding the original oil/gas in place and also the flow properties of the rock matrix. Pore with different properties such as pore size and pore shape can impact the physical, mechanical and chemical properties including strength, elastic modulus, permeability and conductivity. Nowadays, image analysis has been a robust method to quantify the pore information from the porous medium.SEM has been one of the most useful tools to study the pore microstructures due to its high depth of focus which can provide detailed topographical information about the surface. The suitable difference between solid matrix and pores due to the different gray level pixels can be used to study the pore structures.In this paper, we characterized and quantified the pore structures of rock samples from Middle Bakken Formation which is a typical unconventional reservoir in North America. High resolution SEM images of five samples we chose based on the gamma logs were derived after sample preparation. After determining the threshold of the images, we extracted the pore spaces. Then we analyzed the pore structures properties such as pore size distributions and pore shape distributions of the five samples and compared based on their mineral compositions. After that, we analyzed their heterogeneity and isotropy properties which have been identified as an important factor affecting reservoir productivity. Finally, we studied the impact of scale effect on the pore structures characterization.

Pore-scale spectral induced polarization (SIP) signaturesassociated with FeS biomineral transformations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Slater, Lee; Ntarlagiannis, Dimitrios; Personna, Yves R.

2007-10-01

The authors measured Spectral Induced Polarization (SIP) signatures in sand columns during (1) FeS biomineralization produced by sulfate reducing bacteria (D. vulgaris) under anaerboci conditions, and (2) subsequent biomineral dissolution upon return to an aerobic state. The low-frequency (0.1-10 Hz peak) relaxations produced during biomineralization can be modeled with a Cole-Cole formulation, from which the evolution of the polarization magnitude and relaxation length scale can be estimated. They find that the modeled time constant is consistent with the polarizable elements being biomineral encrused pores. Evolution of the model parameters is consistent with FeS surface area increases and pore-size reduction duringmore » biomineral growth, and subsequent biomineral dissolution (FeS surface area decreases and pore expansion) upon return to the aerobic state. They conclude that SIP signatures are diagnostic of pore-scale geometrical changes associated with FeS biomineralization by sulfate reducing bacteria.« less

Micro/Nano-pore Network Analysis of Gas Flow in Shale Matrix

PubMed Central

Zhang, Pengwei; Hu, Liming; Meegoda, Jay N.; Gao, Shengyan

2015-01-01

The gas flow in shale matrix is of great research interests for optimized shale gas extraction. The gas flow in the nano-scale pore may fall in flow regimes such as viscous flow, slip flow and Knudsen diffusion. A 3-dimensional nano-scale pore network model was developed to simulate dynamic gas flow, and to describe the transient properties of flow regimes. The proposed pore network model accounts for the various size distributions and low connectivity of shale pores. The pore size, pore throat size and coordination number obey normal distribution, and the average values can be obtained from shale reservoir data. The gas flow regimes were simulated using an extracted pore network backbone. The numerical results show that apparent permeability is strongly dependent on pore pressure in the reservoir and pore throat size, which is overestimated by low-pressure laboratory tests. With the decrease of reservoir pressure, viscous flow is weakening, then slip flow and Knudsen diffusion are gradually becoming dominant flow regimes. The fingering phenomenon can be predicted by micro/nano-pore network for gas flow, which provides an effective way to capture heterogeneity of shale gas reservoir. PMID:26310236

Micro/Nano-pore Network Analysis of Gas Flow in Shale Matrix.

PubMed

Zhang, Pengwei; Hu, Liming; Meegoda, Jay N; Gao, Shengyan

2015-08-27

The gas flow in shale matrix is of great research interests for optimized shale gas extraction. The gas flow in the nano-scale pore may fall in flow regimes such as viscous flow, slip flow and Knudsen diffusion. A 3-dimensional nano-scale pore network model was developed to simulate dynamic gas flow, and to describe the transient properties of flow regimes. The proposed pore network model accounts for the various size distributions and low connectivity of shale pores. The pore size, pore throat size and coordination number obey normal distribution, and the average values can be obtained from shale reservoir data. The gas flow regimes were simulated using an extracted pore network backbone. The numerical results show that apparent permeability is strongly dependent on pore pressure in the reservoir and pore throat size, which is overestimated by low-pressure laboratory tests. With the decrease of reservoir pressure, viscous flow is weakening, then slip flow and Knudsen diffusion are gradually becoming dominant flow regimes. The fingering phenomenon can be predicted by micro/nano-pore network for gas flow, which provides an effective way to capture heterogeneity of shale gas reservoir.

Pore-scale observation and 3D simulation of wettability effects on supercritical CO2 - brine immiscible displacement in drainage

NASA Astrophysics Data System (ADS)

Hu, R.; Wan, J.; Chen, Y.

2016-12-01

Wettability is a factor controlling the fluid-fluid displacement pattern in porous media and significantly affects the flow and transport of supercritical (sc) CO2 in geologic carbon sequestration. Using a high-pressure micromodel-microscopy system, we performed drainage experiments of scCO2 invasion into brine-saturated water-wet and intermediate-wet micromodels; we visualized the scCO2 invasion morphology at pore-scale under reservoir conditions. We also performed pore-scale numerical simulations of the Navier-Stokes equations to obtain 3D details of fluid-fluid displacement processes. Simulation results are qualitatively consistent with the experiments, showing wider scCO2 fingering, higher percentage of scCO2 and more compact displacement pattern in intermediate-wet micromodel. Through quantitative analysis based on pore-scale simulation, we found that the reduced wettability reduces the displacement front velocity, promotes the pore-filling events in the longitudinal direction, delays the breakthrough time of invading fluid, and then increases the displacement efficiency. Simulated results also show that the fluid-fluid interface area follows a unified power-law relation with scCO2 saturation, and show smaller interface area in intermediate-wet case which suppresses the mass transfer between the phases. These pore-scale results provide insights for the wettability effects on CO2 - brine immiscible displacement in geologic carbon sequestration.

Investigation of Coupled model of Pore network and Continuum in shale gas

NASA Astrophysics Data System (ADS)

Cao, G.; Lin, M.

2016-12-01

Flow in shale spanning over many scales, makes the majority of conventional treatment methods disabled. For effectively simulating, a coupled model of pore-scale and continuum-scale was proposed in this paper. Based on the SEM image, we decompose organic-rich-shale into two subdomains: kerogen and inorganic matrix. In kerogen, the nanoscale pore-network is the main storage space and migration pathway so that the molecular phenomena (slip and diffusive transport) is significant. Whereas, inorganic matrix, with relatively large pores and micro fractures, the flow is approximate to Darcy. We use pore-scale network models (PNM) to represent kerogen and continuum-scale models (FVM or FEM) to represent matrix. Finite element mortars are employed to couple pore- and continuum-scale models by enforcing continuity of pressures and fluxes at shared boundary interfaces. In our method, the process in the coupled model is described by pressure square equation, and uses Dirichlet boundary conditions. We discuss several problems: the optimal element number of mortar faces, two categories boundary faces of pore network, the difference between 2D and 3D models, and the difference between continuum models FVM and FEM in mortars. We conclude that: (1) too coarse mesh in mortars will decrease the accuracy, while too fine mesh will lead to an ill-condition even singular system, the optimal element number is depended on boundary pores and nodes number. (2) pore network models are adjacent to two different mortar faces (PNM to PNM, PNM to continuum model), incidental repeated mortar nodes must be deleted. (3) 3D models can be replaced by 2D models under certain condition. (4) FVM is more convenient than FEM, for its simplicity in assigning interface nodes pressure and calculating interface fluxes. This work is supported by the Strategic Priority Research Program of the Chinese Academy of Sciences (XDB10020302), the 973 Program (2014CB239004), the Key Instrument Developing Project of the CAS (ZDYZ2012-1-08-02), the National Natural Science Foundation of China (41574129).

Toward direct pore-scale modeling of three-phase displacements

NASA Astrophysics Data System (ADS)

Mohammadmoradi, Peyman; Kantzas, Apostolos

2017-12-01

A stable spreading film between water and gas can extract a significant amount of bypassed non-aqueous phase liquid (NAPL) through immiscible three-phase gas/water injection cycles. In this study, the pore-scale displacement mechanisms by which NAPL is mobilized are incorporated into a three-dimensional pore morphology-based model under water-wet and capillary equilibrium conditions. The approach is pixel-based and the sequence of invasions is determined by the fluids' connectivity and the threshold capillary pressure of the advancing interfaces. In addition to the determination of three-phase spatial saturation profiles, residuals, and capillary pressure curves, dynamic finite element simulations are utilized to predict the effective permeabilities of the rock microtomographic images as reasonable representations of the geological formations under study. All the influential features during immiscible fluid flow in pore-level domains including wetting and spreading films, saturation hysteresis, capillary trapping, connectivity, and interface development strategies are taken into account. The capabilities of the model are demonstrated by the successful prediction of saturation functions for Berea sandstone and the accurate reconstruction of three-phase fluid occupancies through a micromodel.

Unifying Pore Network Modeling, Continuous Time Random Walk Theory and Experiment - Accomplishments and Future Directions

NASA Astrophysics Data System (ADS)

Bijeljic, B.

2008-05-01

This talk will describe and highlight the advantages offered by a methodology that unifies pore network modeling, CTRW theory and experiment in description of solute dispersion in porous media. Solute transport in a porous medium is characterized by the interplay of advection and diffusion (described by Peclet number, Pe) that cause spreading of solute particles. This spreading is traditionally described by dispersion coefficients, D, defined by σ 2 = 2Dt, where σ 2 is the variance of the solute position and t is the time. Using a pore-scale network model based on particle tracking, the rich Peclet- number dependence of dispersion coefficient is predicted from first principles and is shown to compare well with experimental data for restricted diffusion, transition, power-law and mechanical dispersion regimes in the asymptotic limit. In the asymptotic limit D is constant and can be used in an averaged advection-dispersion equation. However, it is highly important to recognize that, until the velocity field is fully sampled, the particle transport is non-Gaussian and D possesses temporal or spatial variation. Furthermore, temporal probability density functions (PDF) of tracer particles are studied in pore networks and an excellent agreement for the spectrum of transition times for particles from pore to pore is obtained between network model results and CTRW theory. Based on the truncated power-law interpretation of PDF-s, the physical origin of the power-law scaling of dispersion coefficient vs. Peclet number has been explained for unconsolidated porous media, sands and a number of sandstones, arriving at the same conclusion from numerical network modelling, analytic CTRW theory and experiment. Future directions for further applications of the methodology presented are discussed in relation to the scale- dependent solute dispersion and reactive transport. Significance of pre-asymptotic dispersion in porous media is addressed from pore-scale upwards and the impact of heterogeneity is discussed. The length traveled by solute plumes before Gaussian behaviour is reached increases with an increase in heterogeneity and/or Pe. This opens up the question on the nature of dispersion in natural systems where the heterogeneities at the larger scales will profoundly increase the range of velocities in the aquifer, thus considerably delaying the asymptotic approach to Gaussian behaviour. As a consequence, the asymptotic behaviour might not be reached at the field scale.

Transport of Cryptosporidium parvum Oocysts in Charge Heterogeneous Porous Media: Microfluidics Experiment and Numerical Simulation

NASA Astrophysics Data System (ADS)

Liu, Y.; Meng, X.; Guo, Z.; Zhang, C.; Nguyen, T. H.; Hu, D.; Ji, J.; Yang, X.

2017-12-01

Colloidal attachment on charge heterogeneous grains has significant environmental implications for transport of hazardous colloids, such as pathogens, in the aquifer, where iron, manganese, and aluminium oxide minerals are the major source of surface charge heterogeneity of the aquifer grains. A patchwise surface charge model is often used to describe the surface charge heterogeneity of the grains. In the patchwise model, the colloidal attachment efficiency is linearly correlated with the fraction of the favorable patches (θ=λ(θf - θu)+θu). However, our previous microfluidic study showed that the attachment efficiency of oocysts of Cryptosporidium parvum, a waterborne protozoan parasite, was not linear correlated with the fraction of the favorable patches (λ). In this study, we developed a pore scale model to simulate colloidal transport and attachment on charge heterogeneous grains. The flow field was simulated using the LBM method and colloidal transport and attachment were simulated using the Lagrange particle tracking method. The pore scale model was calibrated with experimental results of colloidal and oocyst transport in microfluidic devices and was then used to simulate oocyst transport in charge heterogeneous porous media under a variety of environmental relative conditions, i.e. the fraction of favorable patchwise, ionic strength, and pH. The results of the pore scale simulations were used to evaluate the effect of surface charge heterogeneity on upscaling of oocyst transport from pore to continuum scale and to develop an applicable correlation between colloidal attachment efficiency and the fraction of the favorable patches.

Pore space analysis of NAPL distribution in sand-clay media

USGS Publications Warehouse

Matmon, D.; Hayden, N.J.

2003-01-01

This paper introduces a conceptual model of clays and non-aqueous phase liquids (NAPLs) at the pore scale that has been developed from a mathematical unit cell model, and direct micromodel observation and measurement of clay-containing porous media. The mathematical model uses a unit cell concept with uniform spherical grains for simulating the sand in the sand-clay matrix (???10% clay). Micromodels made with glass slides and including different clay-containing porous media were used to investigate the two clays (kaolinite and montmorillonite) and NAPL distribution within the pore space. The results were used to understand the distribution of NAPL advancing into initially saturated sand and sand-clay media, and provided a detailed analysis of the pore-scale geometry, pore size distribution, NAPL entry pressures, and the effect of clay on this geometry. Interesting NAPL saturation profiles were observed as a result of the complexity of the pore space geometry with the different packing angles and the presence of clays. The unit cell approach has applications for enhancing the mechanistic understanding and conceptualization, both visually and mathematically, of pore-scale processes such as NAPL and clay distribution. ?? 2003 Elsevier Science Ltd. All rights reserved.

Structure and dynamics of a silica melt in neutral confinement

NASA Astrophysics Data System (ADS)

Geske, Julian; Drossel, Barbara; Vogel, Michael

2017-04-01

We analyze the effects of spatial confinement on viscous silica using molecular dynamics simulations. For this purpose, we prepare a silica melt in a cylindrical pore, which is produced by pinning appropriate fractions of silicon and oxygen atoms in a bulk system after an equilibration period. In this way, the structure of the confined silica melt remains unaffected, while the confinement has a strong impact on the dynamics. We find that the structural relaxation of viscous silica is slowed down according to a double exponential law when approaching the pore wall. Moreover, we observe that static density correlations exist in the vicinity of the pore wall. Based on these effects, we determine dynamical and structural length scales of the silica melt. Both length scales show a similar increase upon cooling, with values on the order of the next-neighbor distances in the studied temperature range. Interestingly, we find no evidence that the growth of the length scales is affected by a fragile-to-strong transition of the silica melt. This observation casts serious doubts on the relevance of these length scales for the structural relaxation, at least for the studied glass former.

Structure and dynamics of a silica melt in neutral confinement.

PubMed

Geske, Julian; Drossel, Barbara; Vogel, Michael

2017-04-07

We analyze the effects of spatial confinement on viscous silica using molecular dynamics simulations. For this purpose, we prepare a silica melt in a cylindrical pore, which is produced by pinning appropriate fractions of silicon and oxygen atoms in a bulk system after an equilibration period. In this way, the structure of the confined silica melt remains unaffected, while the confinement has a strong impact on the dynamics. We find that the structural relaxation of viscous silica is slowed down according to a double exponential law when approaching the pore wall. Moreover, we observe that static density correlations exist in the vicinity of the pore wall. Based on these effects, we determine dynamical and structural length scales of the silica melt. Both length scales show a similar increase upon cooling, with values on the order of the next-neighbor distances in the studied temperature range. Interestingly, we find no evidence that the growth of the length scales is affected by a fragile-to-strong transition of the silica melt. This observation casts serious doubts on the relevance of these length scales for the structural relaxation, at least for the studied glass former.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yoon, Hongkyu; Major, Jonathan; Dewers, Thomas

Dissolved CO 2 in the subsurface resulting from geological CO 2 storage may react with minerals in fractured rocks, confined aquifers, or faults, resulting in mineral precipitation and dissolution. The overall rate of reaction can be affected by coupled processes including hydrodynamics, transport, and reactions at the (sub) pore-scale. In this work pore-scale modeling of coupled fluid flow, reactive transport, and heterogeneous reactions at the mineral surface is applied to account for permeability alterations caused by precipitation-induced pore-blocking. This paper is motivated by observations of CO 2 seeps from a natural CO 2 sequestration analog, Crystal Geyser, Utah. Observations alongmore » the surface exposure of the Little Grand Wash fault indicate the lateral migration of CO 2 seep sites (i.e., alteration zones) of 10–50 m width with spacing on the order of ~100 m over time. Sandstone permeability in alteration zones is reduced by 3–4 orders of magnitude by carbonate cementation compared to unaltered zones. One granular porous medium and one fracture network systems are used to conceptually represent permeable porous media and locations of conduits controlled by fault-segment intersections and/or topography, respectively. Simulation cases accounted for a range of reaction regimes characterized by the Damköhler (Da) and Peclet (Pe) numbers. Pore-scale simulation results demonstrate that combinations of transport (Pe), geochemical conditions (Da), solution chemistry, and pore and fracture configurations contributed to match key patterns observed in the field of how calcite precipitation alters flow paths by pore plugging. This comparison of simulation results with field observations reveals mechanistic explanations of the lateral migration and enhances our understanding of subsurface processes associated with the CO 2 injection. In addition, permeability and porosity relations are constructed from pore-scale simulations which account for a range of reaction regimes characterized by the Da and Pe numbers. Finally, the functional relationships obtained from pore-scale simulations can be used in a continuum scale model that may account for large-scale phenomena mimicking lateral migration of surface CO 2 seeps.« less

Pore configuration landscape of granular crystallization.

PubMed

Saadatfar, M; Takeuchi, H; Robins, V; Francois, N; Hiraoka, Y

2017-05-12

Uncovering grain-scale mechanisms that underlie the disorder-order transition in assemblies of dissipative, athermal particles is a fundamental problem with technological relevance. To date, the study of granular crystallization has mainly focussed on the symmetry of crystalline patterns while their emergence and growth from irregular clusters of grains remains largely unexplored. Here crystallization of three-dimensional packings of frictional spheres is studied at the grain-scale using X-ray tomography and persistent homology. The latter produces a map of the topological configurations of grains within static partially crystallized packings. Using numerical simulations, we show that similar maps are measured dynamically during the melting of a perfect crystal. This map encodes new information on the formation process of tetrahedral and octahedral pores, the building blocks of perfect crystals. Four key formation mechanisms of these pores reproduce the main changes of the map during crystallization and provide continuous deformation pathways representative of the crystallization dynamics.

Pore configuration landscape of granular crystallization

PubMed Central

Saadatfar, M.; Takeuchi, H.; Robins, V.; Francois, N.; Hiraoka, Y.

2017-01-01

Uncovering grain-scale mechanisms that underlie the disorder–order transition in assemblies of dissipative, athermal particles is a fundamental problem with technological relevance. To date, the study of granular crystallization has mainly focussed on the symmetry of crystalline patterns while their emergence and growth from irregular clusters of grains remains largely unexplored. Here crystallization of three-dimensional packings of frictional spheres is studied at the grain-scale using X-ray tomography and persistent homology. The latter produces a map of the topological configurations of grains within static partially crystallized packings. Using numerical simulations, we show that similar maps are measured dynamically during the melting of a perfect crystal. This map encodes new information on the formation process of tetrahedral and octahedral pores, the building blocks of perfect crystals. Four key formation mechanisms of these pores reproduce the main changes of the map during crystallization and provide continuous deformation pathways representative of the crystallization dynamics. PMID:28497794

Pore configuration landscape of granular crystallization

NASA Astrophysics Data System (ADS)

Saadatfar, M.; Takeuchi, H.; Robins, V.; Francois, N.; Hiraoka, Y.

2017-05-01

Uncovering grain-scale mechanisms that underlie the disorder-order transition in assemblies of dissipative, athermal particles is a fundamental problem with technological relevance. To date, the study of granular crystallization has mainly focussed on the symmetry of crystalline patterns while their emergence and growth from irregular clusters of grains remains largely unexplored. Here crystallization of three-dimensional packings of frictional spheres is studied at the grain-scale using X-ray tomography and persistent homology. The latter produces a map of the topological configurations of grains within static partially crystallized packings. Using numerical simulations, we show that similar maps are measured dynamically during the melting of a perfect crystal. This map encodes new information on the formation process of tetrahedral and octahedral pores, the building blocks of perfect crystals. Four key formation mechanisms of these pores reproduce the main changes of the map during crystallization and provide continuous deformation pathways representative of the crystallization dynamics.

Shock Waves and Defects in Energetic Materials, a Match Made in MD Heaven

NASA Astrophysics Data System (ADS)

Wood, Mitchell; Kittell, David; Yarrington, Cole; Thompson, Aidan

2017-06-01

Shock wave interactions with defects, such as pores, are known to play a key role in the chemical initiation of energetic materials. In this talk the shock response of Hexanitrostilbene (HNS) is studied through large scale reactive molecular dynamics (RMD) simulations. These RMD simulations provide a unique opportunity to elucidate mechanisms of viscoplastic pore collapse which are often neglected in larger scale hydrodynamic models. A discussion of the macroscopic effects of this viscoplastic material response, such as its role in hot spot formation and eventual initiation, will be provided. Through this work we have been able to map a transition from purely viscoplastic to fluid-like pore collapse that is a function of shock strength, pore size and material strength. In addition, these findings are important reference data for the validation of future multi-scale modeling efforts of the shock response of heterogeneous materials. Examples of how these RMD results are translated into mesoscale models will also be addressed. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the US DOE NNSA under Contract No. DE- AC04-94AL85000.

Multiscale pore structure and its effect on gas transport in organic-rich shale

NASA Astrophysics Data System (ADS)

Wu, Tianhao; Li, Xiang; Zhao, Junliang; Zhang, Dongxiao

2017-07-01

A systematic investigation of multiscale pore structure in organic-rich shale by means of the combination of various imaging techniques is presented, including the state-of-the-art Helium-Ion-Microscope (HIM). The study achieves insight into the major features at each scale and suggests the affordable techniques for specific objectives from the aspects of resolution, dimension, and cost. The pores, which appear to be isolated, are connected by smaller pores resolved by higher-resolution imaging. This observation provides valuable information, from the microscopic perspective of pore structure, for understanding how gas accumulates and transports from where it is generated. A comprehensive workflow is proposed based on the characteristics acquired from the multiscale pore structure analysis to simulate the gas transport process. The simulations are completed with three levels: the microscopic mechanisms should be taken into consideration at level I; the spatial distribution features of organic matter, inorganic matter, and macropores constitute the major issue at level II; and the microfracture orientation and topological structure are dominant factors at level III. The results of apparent permeability from simulations agree well with the values acquired from experiments. By means of the workflow, the impact of various gas transport mechanisms at different scales can be investigated more individually and precisely than conventional experiments.

Toward multiscale modelings of grain-fluid systems

NASA Astrophysics Data System (ADS)

Chareyre, Bruno; Yuan, Chao; Montella, Eduard P.; Salager, Simon

2017-06-01

Computationally efficient methods have been developed for simulating partially saturated granular materials in the pendular regime. In contrast, one hardly avoid expensive direct resolutions of 2-phase fluid dynamics problem for mixed pendular-funicular situations or even saturated regimes. Following previous developments for single-phase flow, a pore-network approach of the coupling problems is described. The geometry and movements of phases and interfaces are described on the basis of a tetrahedrization of the pore space, introducing elementary objects such as bridge, meniscus, pore body and pore throat, together with local rules of evolution. As firmly established local rules are still missing on some aspects (entry capillary pressure and pore-scale pressure-saturation relations, forces on the grains, or kinetics of transfers in mixed situations) a multi-scale numerical framework is introduced, enhancing the pore-network approach with the help of direct simulations. Small subsets of a granular system are extracted, in which multiphase scenario are solved using the Lattice-Boltzman method (LBM). In turns, a global problem is assembled and solved at the network scale, as illustrated by a simulated primary drainage.

Permeability measurements on rock samples from Unzen Scientific Drilling Project Drill Hole 4 (USDP-4)

NASA Astrophysics Data System (ADS)

Watanabe, Tohru; Shimizu, Yuhta; Noguchi, Satoshi; Nakada, Setsuya

2008-07-01

Permeability measurement was made on five rock samples from USDP-4 cores. Rock samples were collected from the conduit zone and its country rock. One sample (C14-1-1) is considered as a part of the feeder dyke for the 1991-1995 eruption. The transient pulse method was employed under confining pressure up to 50 MPa. Compressional wave velocity was measured along with permeability. The measured permeability ranges from 10 - 19 to 10 - 17 m 2 at the atmospheric pressure, and is as low as that reported for tight rocks such as granite. The permeability decreases with increasing confining pressure, while the compressional wave velocity increases. Assuming that pores are parallel elliptical tubes, the pressure dependence of permeability requires aspect ratio of 10 - 4 -10 - 2 at the atmospheric pressure. The pore aperture is estimated to be less than 1 μm. The estimated aspect ratio and pore aperture suggest that connectivity of pores is maintained by narrow cracks. The existence of cracks is supported by the pressure dependence of compressional wave velocity. Narrow cracks (< 1 μm) are observed in dyke samples, and they must have been created after solidification. Dyke samples do not provide us information of pore structures during degassing, since exsolved gas has mostly escaped and pores governing the gas permeable flow should have been lost. Both dyke and country rock samples provide us information of materials around ascending magma. Although the measured small-scale permeability cannot be directly applied to geological-scale processes, it gives constrains on studies of large-scale permeability.

Fast laboratory-based micro-computed tomography for pore-scale research: Illustrative experiments and perspectives on the future

NASA Astrophysics Data System (ADS)

Bultreys, Tom; Boone, Marijn A.; Boone, Matthieu N.; De Schryver, Thomas; Masschaele, Bert; Van Hoorebeke, Luc; Cnudde, Veerle

2016-09-01

Over the past decade, the wide-spread implementation of laboratory-based X-ray micro-computed tomography (micro-CT) scanners has revolutionized both the experimental and numerical research on pore-scale transport in geological materials. The availability of these scanners has opened up the possibility to image a rock's pore space in 3D almost routinely to many researchers. While challenges do persist in this field, we treat the next frontier in laboratory-based micro-CT scanning: in-situ, time-resolved imaging of dynamic processes. Extremely fast (even sub-second) micro-CT imaging has become possible at synchrotron facilities over the last few years, however, the restricted accessibility of synchrotrons limits the amount of experiments which can be performed. The much smaller X-ray flux in laboratory-based systems bounds the time resolution which can be attained at these facilities. Nevertheless, progress is being made to improve the quality of measurements performed on the sub-minute time scale. We illustrate this by presenting cutting-edge pore scale experiments visualizing two-phase flow and solute transport in real-time with a lab-based environmental micro-CT set-up. To outline the current state of this young field and its relevance to pore-scale transport research, we critically examine its current bottlenecks and their possible solutions, both on the hardware and the software level. Further developments in laboratory-based, time-resolved imaging could prove greatly beneficial to our understanding of transport behavior in geological materials and to the improvement of pore-scale modeling by providing valuable validation.

The effects of burial diagenesis on multiscale porosity in the St. Peter Sandstone: An imaging, small-angle, and ultra-small-angle neutron scattering analysis

DOE PAGES

Anovitz, Lawrence M.; Freiburg, Jared T.; Wasbrough, Matthew; ...

2017-11-06

To examine the effects of burial diagenesis on heirarchical pore structures in sandstone and compare those with the effects of overgrowth formation, we obtained samples of St. Peter Sandstone from drill cores obtained in the Illinois and Michigan Basins. The multiscale pore structure of rocks in sedimentary reservoirs and the mineralogy associated with those pores are critical factors for estimating reservoir properties, including fluid mass in place, permeability, and capillary pressures, as well as geochemical interactions between the rock and the fluid. The combination of small- and ultra-small-angle neutron scattering with backscattered electron or X ray-computed tomographic imaging, or both,more » provided a means by which pore structures were quantified at scales ranging from aproximately 1 nm to 1 cm—seven orders of magnitude. Larger scale (>10 µm) porosity showed the expected logarithmic decrease in porosity with depth, although there was significant variation in each sample group. However, small- and ultra-small-angle neutron scattering data showed that the proportion of small-scale porosity increased with depth. Porosity distributions were not continuous, but consisted of a series of log normal-like distributions at several distinct scales within these rocks. Fractal dimensions at larger scales decreased (surfaces smoothed) with increasing depth, and those at smaller scales increased (surfaces roughened) and pores become more isolated (higher lacunarity). Furthermore, data suggest that changes in pore-size distributions are controlled by both physical (compaction) and chemical effects (precipitation, cementation, dissolution).« less

The effects of burial diagenesis on multiscale porosity in the St. Peter Sandstone: An imaging, small-angle, and ultra-small-angle neutron scattering analysis

DOE Office of Scientific and Technical Information (OSTI.GOV)

Anovitz, Lawrence M.; Freiburg, Jared T.; Wasbrough, Matthew

To examine the effects of burial diagenesis on heirarchical pore structures in sandstone and compare those with the effects of overgrowth formation, we obtained samples of St. Peter Sandstone from drill cores obtained in the Illinois and Michigan Basins. The multiscale pore structure of rocks in sedimentary reservoirs and the mineralogy associated with those pores are critical factors for estimating reservoir properties, including fluid mass in place, permeability, and capillary pressures, as well as geochemical interactions between the rock and the fluid. The combination of small- and ultra-small-angle neutron scattering with backscattered electron or X ray-computed tomographic imaging, or both,more » provided a means by which pore structures were quantified at scales ranging from aproximately 1 nm to 1 cm—seven orders of magnitude. Larger scale (>10 µm) porosity showed the expected logarithmic decrease in porosity with depth, although there was significant variation in each sample group. However, small- and ultra-small-angle neutron scattering data showed that the proportion of small-scale porosity increased with depth. Porosity distributions were not continuous, but consisted of a series of log normal-like distributions at several distinct scales within these rocks. Fractal dimensions at larger scales decreased (surfaces smoothed) with increasing depth, and those at smaller scales increased (surfaces roughened) and pores become more isolated (higher lacunarity). Furthermore, data suggest that changes in pore-size distributions are controlled by both physical (compaction) and chemical effects (precipitation, cementation, dissolution).« less

Pore characteristics and their emergent effect on water adsorption and transport in clays using small-angle neutron scattering with contrast variation

NASA Astrophysics Data System (ADS)

Ding, M.; Hartl, M.; Wang, Y.; Hjelm, R.

2013-12-01

In nuclear waste management, clays are canonical materials in the construction of engineered barriers. They are also naturally occurring reactive minerals which play an important role in retention and colloidal facilitated reactive transport in subsurface systems. Knowledge of total and accessible porosity in clays is crucial in determining fluids transport behavior in clays. It will provide fundamental insight on the performance efficiency of specific clays as a barrier material and their role in regulating radionuclide transport in subsurface environments. The aim of the present work is to experimentally investigate the change in pore characteristics of clays as function of moisture content, and to determine their pore character in relation to their water retention capacity. Recent developments in small-angle neutron scattering (SANS) techniques allow quantitative measurement of pore morphology and size distribution of various materials in their pristine state under various sample environments (exposure to solution, high temperature, and so on). Furthermore, due to dramatic different neutron scattering properties of hydrogen and deuterium, one can readily use contrast variation, which is the isotopic labeling with various ratios of H and D (e.g. mixture of H2O/D2O) to highlight or suppress features of the sample. This is particularly useful in the study of complex pore system such as clays. In this study, we have characterized the pore structures for a number of clays including clay minerals and field samples which are relevant to high-level waste systems under various sample environments (e.g., humidity, temperature and pressure) using SANS. Our results suggest that different clays show unique pore features under various sample environments. To distinguish between accessible/non-accessible pores and the nature of pore filling (e.g. the quantity of H2O adsorbed by clays, and the distribution of H2O in relation to pore character) to water, clays were exposed for various periods to a specific humidity (e.g., relative humidity: RH=100%, RH=75%). The humidity is controlled by using saturated aqueous solutions, consisting of specific H2O/D2O mixtures. Our results have shown distinct variations in water adsorption and moisture diffusivity among clays. Our results allow us to obtain on the pore scale porosity changes due to water movement in clays. As emergent transport property, nano- to micro-scale structural characterization is crucial in providing insights into pore-scale transport processes, which are pertinent to upscale continuum model development involving flow and transport at low water content, flow and phase behavior under confinement, and low-permeability media.

Rapid Polymer Transport in a Single Nanometer-Scale Pore

NASA Astrophysics Data System (ADS)

Kasianowicz, J. J.

1998-03-01

Protein ion channels are nanometer-scale pores that control the transport of ions and polymers across cell membranes. We compared the ability of charged and nonelectrolyte linear polymers to partition into a single channel reconstituted into a planar lipid bilayer membrane. The entry of each polymer (e.g. monodisperse length single-stranded homopolymeric RNA1 or poly(ethylene glycol)2,3) into the pore caused characteristic transient decreases in the channel's ionic conductance. The ionic current blockades yield detailed information about the physical properties of the polymers and the pore. The biological and technological significance of the results will be discussed.

Partitioning of habitable pore space in earthworm burrows.

PubMed

Gorres, Josef H; Amador, Jose A

2010-03-01

Earthworms affect macro-pore structure of soils. However, some studies suggest that earthworm burrow walls and casts themselves differ greatly in structure from surrounding soils, potentially creating habitat for microbivorours nematodes which accelerate the decomposition and C and N mineralization. In this study aggregates were sampled from the burrow walls of the anecic earthworm Lumbricus terrestris and bulk soil (not altered by earthworms) from mesocosm incubated in the lab for 0, 1, 3, 5 and 16 weeks. Pore volumes and pore sizes were measured in triplicate with Mercury Intrusion Porosimetry (MIP). This method is well suited to establish pore size structure in the context of habitat, because it measures the stepwise intrusion of mercury from the outside of the aggregate into ever smaller pores. The progress of mercury into the aggregate interior thus resembles potential paths of a nematode into accessible habitable pore spaces residing in an aggregate. Total specific pore volume, V(s), varied between 0.13 and 0.18 mL/g and increased from 3 to 16 weeks in both burrow and bulk soil. Differences between total V(s) of bulk and burrow samples were not significant on any sampling date. However, differences were significant for pore size fractions at the scale of nematode body diameter.

Partitioning of habitable pore space in earthworm burrows

PubMed Central

Amador, Jose A.

2010-01-01

Earthworms affect macro-pore structure of soils. However, some studies suggest that earthworm burrow walls and casts themselves differ greatly in structure from surrounding soils, potentially creating habitat for microbivorours nematodes which accelerate the decomposition and C and N mineralization. In this study aggregates were sampled from the burrow walls of the anecic earthworm Lumbricus terrestris and bulk soil (not altered by earthworms) from mesocosm incubated in the lab for 0, 1, 3, 5 and 16 weeks. Pore volumes and pore sizes were measured in triplicate with Mercury Intrusion Porosimetry (MIP). This method is well suited to establish pore size structure in the context of habitat, because it measures the stepwise intrusion of mercury from the outside of the aggregate into ever smaller pores. The progress of mercury into the aggregate interior thus resembles potential paths of a nematode into accessible habitable pore spaces residing in an aggregate. Total specific pore volume, Vs, varied between 0.13 and 0.18 mL/g and increased from 3 to 16 weeks in both burrow and bulk soil. Differences between total Vs of bulk and burrow samples were not significant on any sampling date. However, differences were significant for pore size fractions at the scale of nematode body diameter. PMID:22736839

Capillary filling rules and displacement mechanisms for spontaneous imbibition of CO2 for carbon storage and EOR using micro-model experiments and pore scale simulation

NASA Astrophysics Data System (ADS)

Chapman, E.; Yang, J.; Crawshaw, J.; Boek, E. S.

2012-04-01

In the 1980s, Lenormand et al. carried out their pioneering work on displacement mechanisms of fluids in etched networks [1]. Here we further examine displacement mechanisms in relation to capillary filling rules for spontaneous imbibition. Understanding the role of spontaneous imbibition in fluid displacement is essential for refining pore network models. Generally, pore network models use simple capillary filling rules and here we examine the validity of these rules for spontaneous imbibition. Improvement of pore network models is vital for the process of 'up-scaling' to the field scale for both enhanced oil recovery (EOR) and carbon sequestration. In this work, we present our experimental microfluidic research into the displacement of both supercritical CO2/deionised water (DI) systems and analogous n-decane/air - where supercritical CO2 and n-decane are the respective wetting fluids - controlled by imbibition at the pore scale. We conducted our experiments in etched PMMA and silicon/glass micro-fluidic hydrophobic chips. We first investigate displacement in single etched pore junctions, followed by displacement in complex network designs representing actual rock thin sections, i.e. Berea sandstone and Sucrosic dolomite. The n-decane/air experiments were conducted under ambient conditions, whereas the supercritical CO2/DI water experiments were conducted under high temperature and pressure in order to replicate reservoir conditions. Fluid displacement in all experiments was captured via a high speed video microscope. The direction and type of displacement the imbibing fluid takes when it enters a junction is dependent on the number of possible channels in which the wetting fluid can imbibe, i.e. I1, I2 and I3 [1]. Depending on the experiment conducted, the micro-models were initially filled with either DI water or air before the wetting fluid was injected. We found that the imbibition of the wetting fluid through a single pore is primarily controlled by the geometry of the pore body rather than the downstream pore throat sizes, contrary to the established capillary filling rules as used in current pore network models. Our experimental observations are confirmed by detailed lattice-Boltzmann pore scale computer simulations of fluid displacement in the same geometries. This suggests that capillary filling rules for imbibition as used in pore network models may need to be revised. [1] G. Lenormand, C. Zarcone and A. Sarr, J. Fluid Mech. 135 , 337-353 (1983).

Final Report for DE-SC0008059

DOE Office of Scientific and Technical Information (OSTI.GOV)

Karnik, Rohit

Graphene, a one-atom thick material comprising hexagonally bonded carbon atoms, is one of the strongest materials known and is impermeable to even helium gas. The potential for creation of tunable nanometer-scale pores in graphene, combined with mechanical strength, chemical resistance, and atomic thickness, make it a promising material for improving selectivity, permeability, and energy efficiency in a diverse range of membrane separations. However, fundamental understanding of creation of porous graphene, its mass transport properties, and the relationship between porosity and membrane performance is lacking. This project studied methods to create pores in graphene by ion irradiation and etching, and investigatedmore » the effect of the porosity of graphene on mass transport properties at the membrane level as well as across individual pores. Detailed characterization of pore size distributions in graphene using high-resolution scanning transmission electron microscopy was performed to elucidate the relationship between different pore creation processes and the resulting porosity. New methods to create tunable nanometer-scale pores in graphene at high density over large areas were developed. Graphene membranes were fabricated comprising single-layer porous graphene on appropriate support membranes. Mass transport of ions, molecules, water, and gases across the membranes was investigated, and predictive models were developed to relate the graphene porosity and support membrane structure to the mass transport properties of the membranes. The effect of graphene porosity on permeance of the membranes to water, salts, and small molecules was experimentally quantified. Single-pore measurements were performed and a model was developed to understand ion transport across graphene pores, which led to the experimental observation of heterogeneity in transport behaviors and spontaneous fluctuations of ion transport. Functional single-layer nanoporous graphene membranes comprising a high density of pores over macro-scale areas with molecular selectivity were demonstrated for the first time. This project led to three patent applications and 9 journal articles. The fundamental developments in understanding nanoporous graphene membranes have laid the foundations to develop energy-efficient nanoporous graphene membranes for various applications in water desalination, oil and natural gas separations, biotechnology, and chemical processing.« less

Unifying Pore Network Modeling, Continuous Time Random Walk (CTRW) Theory and Experiment to Describe Impact of Spatial Heterogeneities on Solute Dispersion at Multiple Length-scales

NASA Astrophysics Data System (ADS)

Bijeljic, B.; Blunt, M. J.; Rhodes, M. E.

2009-04-01

This talk will describe and highlight the advantages offered by a novel methodology that unifies pore network modeling, CTRW theory and experiment in description of solute dispersion in porous media. Solute transport in a porous medium is characterized by the interplay of advection and diffusion (described by Peclet number, Pe) that cause dispersion of solute particles. Dispersion is traditionally described by dispersion coefficients, D, that are commonly calculated from the spatial moments of the plume. Using a pore-scale network model based on particle tracking, the rich Peclet-number dependence of dispersion coefficient is predicted from first principles and is shown to compare well with experimental data for restricted diffusion, transition, power-law and mechanical dispersion regimes in the asymptotic limit. In the asymptotic limit D is constant and can be used in an averaged advection-dispersion equation. However, it is highly important to recognize that, until the velocity field is fully sampled, the particle transport is non-Gaussian and D possesses temporal or spatial variation. Furthermore, temporal probability density functions (PDF) of tracer particles are studied in pore networks and an excellent agreement for the spectrum of transition times for particles from pore to pore is obtained between network model results and CTRW theory. Based on the truncated power-law interpretation of PDF-s, the physical origin of the power-law scaling of dispersion coefficient vs. Peclet number has been explained for unconsolidated porous media, sands and a number of sandstones, arriving at the same conclusion from numerical network modelling, analytic CTRW theory and experiment. The length traveled by solute plumes before Gaussian behaviour is reached increases with an increase in heterogeneity and/or Pe. This opens up the question on the nature of dispersion in natural systems where the heterogeneities at the larger scales will significantly increase the range of velocities in the reservoir, thus significantly delaying the asymptotic approach to Gaussian behaviour. As a consequence, the asymptotic behaviour might not be reached at the field scale. This is illustrated by the multi-scale approach in which transport at core, gridblock and field scale is viewed as a series of particle transitions between discrete nodes governed by probability distributions. At each scale of interest a distribution that represents transport physics (and the heterogeneity) is used as an input to model a subsequent reservoir scale. The extensions to reactive transport are discussed.

Pore architecture of nanoporous gold and titania by hydrogen thermoporometry

DOE PAGES

Johnston, L. T.; Biener, M. M.; Ye, J. C.; ...

2015-07-10

Nanoporous gold (NPG) and materials derived from it by templating have complex pore architecture that determines their technologically relevant physical properties. Here, we apply high-resolution hydrogen thermoporometry to study the pore structure of NPG and NPG-derived titania nanofoam (TNF). Results reveal complex multimodal pore size distributions for NPG and TNF. The freezing–melting hysteresis is pronounced, with freezing and melting scans having entirely different shapes. Experiments involving partial freeze–melt cycles reveal the lack of direct correlation between individual freezing and melting peaks, pointing to phenomena that are beyond the Gibbs-Thomson formalism. The depression of the average freezing temperature scales linearly withmore » the ratio of the internal surface area (measured by gas sorption) and the total pore volume derived from the density of monoliths. In conclusion, thermoporometry yields total pore volumes in good agreement with those derived from monolith densities for both NPG and TNF.« less

Pore architecture of nanoporous gold and titania by hydrogen thermoporometry

DOE Office of Scientific and Technical Information (OSTI.GOV)

Johnston, L. T.; Biener, M. M.; Ye, J. C.

Nanoporous gold (NPG) and materials derived from it by templating have complex pore architecture that determines their technologically relevant physical properties. Here, we apply high-resolution hydrogen thermoporometry to study the pore structure of NPG and NPG-derived titania nanofoam (TNF). Results reveal complex multimodal pore size distributions for NPG and TNF. The freezing–melting hysteresis is pronounced, with freezing and melting scans having entirely different shapes. Experiments involving partial freeze–melt cycles reveal the lack of direct correlation between individual freezing and melting peaks, pointing to phenomena that are beyond the Gibbs-Thomson formalism. The depression of the average freezing temperature scales linearly withmore » the ratio of the internal surface area (measured by gas sorption) and the total pore volume derived from the density of monoliths. In conclusion, thermoporometry yields total pore volumes in good agreement with those derived from monolith densities for both NPG and TNF.« less

Lattice Boltzmann-Based Approaches for Pore-Scale Reactive Transport

DOE PAGES

Yoon, Hongkyu; Kang, Qinjun; Valocchi, Albert J.

2015-07-29

Here an important geoscience and environmental applications such as geologic carbon storage, environmental remediation, and unconventional oil and gas recovery are best understood in the context of reactive flow and multicomponent transport in the subsurface environment. The coupling of chemical and microbiological reactions with hydrological and mechanical processes can lead to complex behaviors across an enormous range of spatial and temporal scales. These coupled responses are also strongly influenced by the heterogeneity and anisotropy of the geologic formations. Reactive transport processes can change the pore morphology at the pore scale, thereby leading to nonlinear interactions with advective and diffusive transport,more » which can strongly influence larger-scale properties such as permeability and dispersion.« less

Pore-scale water dynamics during drying and the impacts of structure and surface wettability

NASA Astrophysics Data System (ADS)

Cruz, Brian C.; Furrer, Jessica M.; Guo, Yi-Syuan; Dougherty, Daniel; Hinestroza, Hector F.; Hernandez, Jhoan S.; Gage, Daniel J.; Cho, Yong Ku; Shor, Leslie M.

2017-07-01

Plants and microbes secrete mucilage into soil during dry conditions, which can alter soil structure and increase contact angle. Structured soils exhibit a broad pore size distribution with many small and many large pores, and strong capillary forces in narrow pores can retain moisture in soil aggregates. Meanwhile, contact angle determines the water repellency of soils, which can result in suppressed evaporation rates. Although they are often studied independently, both structure and contact angle influence water movement, distribution, and retention in soils. Here drying experiments were conducted using soil micromodels patterned to emulate different aggregation states of a sandy loam soil. Micromodels were treated to exhibit contact angles representative of those in bulk soil (8.4° ± 1.9°) and the rhizosphere (65° ± 9.2°). Drying was simulated using a lattice Boltzmann single-component, multiphase model. In our experiments, micromodels with higher contact angle surfaces took 4 times longer to completely dry versus micromodels with lower contact angle surfaces. Microstructure influenced drying rate as a function of saturation and controlled the spatial distribution of moisture within micromodels. Lattice Boltzmann simulations accurately predicted pore-scale moisture retention patterns within micromodels with different structures and contact angles.

Evaluating the Global Precipitation Measurement mission with NOAA/NSSL Multi-Radar Multisensor: current status and future directions.

NASA Astrophysics Data System (ADS)

Kirstetter, P. E.; Petersen, W. A.; Gourley, J. J.; Kummerow, C. D.; Huffman, G. J.; Turk, J.; Tanelli, S.; Maggioni, V.; Anagnostou, E. N.; Hong, Y.; Schwaller, M.

2016-12-01

Natural gas production via hydraulic fracturing of shale has proliferated on a global scale, yet recovery factors remain low because production strategies are not based on the physics of flow in shale reservoirs. In particular, the physical mechanisms and time scales of depletion from the matrix into the simulated fracture network are not well understood, limiting the potential to optimize operations and reduce environmental impacts. Studying matrix flow is challenging because shale is heterogeneous and has porosity from the μm- to nm-scale. Characterizing nm-scale flow paths requires electron microscopy but the limited field of view does not capture the connectivity and heterogeneity observed at the mm-scale. Therefore, pore-scale models must link to larger volumes to simulate flow on the reservoir-scale. Upscaled models must honor the physics of flow, but at present there is a gap between cm-scale experiments and μm-scale simulations based on ex situ image data. To address this gap, we developed a synchrotron X-ray microscope with an in situ cell to simultaneously visualize and measure flow. We perform coupled flow and microtomography experiments on mm-scale samples from the Barnett, Eagle Ford and Marcellus reservoirs. We measure permeability at various pressures via the pulse-decay method to quantify effective stress dependence and the relative contributions of advective and diffusive mechanisms. Images at each pressure step document how microfractures, interparticle pores, and organic matter change with effective stress. Linking changes in the pore network to flow measurements motivates a physical model for depletion. To directly visualize flow, we measure imbibition rates using inert, high atomic number gases and image periodically with monochromatic beam. By imaging above/below X-ray adsorption edges, we magnify the signal of gas saturation in μm-scale porosity and nm-scale, sub-voxel features. Comparing vacuumed and saturated states yields image-based measurements of the distribution and time scales of imbibition. We also characterize nm-scale structure via focused ion beam tomography to quantify sub-voxel porosity and connectivity. The multi-scale image and flow data is used to develop a framework to upscale and benchmark pore-scale models.

Visualizing and measuring flow in shale matrix using in situ synchrotron X-ray microtomography

NASA Astrophysics Data System (ADS)

Kohli, A. H.; Kiss, A. M.; Kovscek, A. R.; Bargar, J.

2017-12-01

Natural gas production via hydraulic fracturing of shale has proliferated on a global scale, yet recovery factors remain low because production strategies are not based on the physics of flow in shale reservoirs. In particular, the physical mechanisms and time scales of depletion from the matrix into the simulated fracture network are not well understood, limiting the potential to optimize operations and reduce environmental impacts. Studying matrix flow is challenging because shale is heterogeneous and has porosity from the μm- to nm-scale. Characterizing nm-scale flow paths requires electron microscopy but the limited field of view does not capture the connectivity and heterogeneity observed at the mm-scale. Therefore, pore-scale models must link to larger volumes to simulate flow on the reservoir-scale. Upscaled models must honor the physics of flow, but at present there is a gap between cm-scale experiments and μm-scale simulations based on ex situ image data. To address this gap, we developed a synchrotron X-ray microscope with an in situ cell to simultaneously visualize and measure flow. We perform coupled flow and microtomography experiments on mm-scale samples from the Barnett, Eagle Ford and Marcellus reservoirs. We measure permeability at various pressures via the pulse-decay method to quantify effective stress dependence and the relative contributions of advective and diffusive mechanisms. Images at each pressure step document how microfractures, interparticle pores, and organic matter change with effective stress. Linking changes in the pore network to flow measurements motivates a physical model for depletion. To directly visualize flow, we measure imbibition rates using inert, high atomic number gases and image periodically with monochromatic beam. By imaging above/below X-ray adsorption edges, we magnify the signal of gas saturation in μm-scale porosity and nm-scale, sub-voxel features. Comparing vacuumed and saturated states yields image-based measurements of the distribution and time scales of imbibition. We also characterize nm-scale structure via focused ion beam tomography to quantify sub-voxel porosity and connectivity. The multi-scale image and flow data is used to develop a framework to upscale and benchmark pore-scale models.

Enhancing Tensile Response of Sn Using Cu at Nano Length Scale and High Temperature Extrusion

DTIC Science & Technology

2009-02-01

temperature extruded Sn-1.1Cu 664 samples suggesting the presence of lenticular pores. This aspect ratio of pores was only 1.7 for high temperature Sn...resulting in filling the voids or breaking the lenticular pores into small pores besides higher atomic diffusion rates [8...relatively round pores were observed for hot extruded Sn-Cu samples that helps to increase the strength. The lenticular pores (higher aspect ratio) in

Influence of capillary end effects on steady-state relative permeability estimates from direct pore-scale simulations

NASA Astrophysics Data System (ADS)

Guédon, Gaël Raymond; Hyman, Jeffrey De'Haven; Inzoli, Fabio; Riva, Monica; Guadagnini, Alberto

2017-12-01

We investigate and characterize the influence of capillary end effects on steady-state relative permeabilities obtained in pore-scale numerical simulations of two-phase flows. Our study is motivated by the observation that capillary end effects documented in two-phase laboratory-scale experiments can significantly influence permeability estimates. While numerical simulations of two-phase flows in reconstructed pore-spaces are increasingly employed to characterize relative permeabilities, a phenomenon which is akin to capillary end effects can also arise in such analyses due to the constraints applied at the boundaries of the computational domain. We profile the relative strength of these capillary end effects on the calculation of steady-state relative permeabilities obtained within randomly generated porous micro-structures using a finite volume-based two-phase flow solver. We suggest a procedure to estimate the extent of the regions influenced by these capillary end effects, which in turn allows for the alleviation of bias in the estimation of relative permeabilities.

Multiscale modeling of shock wave localization in porous energetic material

NASA Astrophysics Data System (ADS)

Wood, M. A.; Kittell, D. E.; Yarrington, C. D.; Thompson, A. P.

2018-01-01

Shock wave interactions with defects, such as pores, are known to play a key role in the chemical initiation of energetic materials. The shock response of hexanitrostilbene is studied through a combination of large-scale reactive molecular dynamics and mesoscale hydrodynamic simulations. In order to extend our simulation capability at the mesoscale to include weak shock conditions (<6 GPa), atomistic simulations of pore collapse are used to define a strain-rate-dependent strength model. Comparing these simulation methods allows us to impose physically reasonable constraints on the mesoscale model parameters. In doing so, we have been able to study shock waves interacting with pores as a function of this viscoplastic material response. We find that the pore collapse behavior of weak shocks is characteristically different than that of strong shocks.

Shifts in pore connectivity from precipitation versus groundwater rewetting increases soil carbon loss after drought

DOE Office of Scientific and Technical Information (OSTI.GOV)

Smith, A. Peyton; Bond-Lamberty, Ben; Benscoter, Brian W.

Droughts and other extreme precipitation events are predicted to increase in intensity, duration and extent, with uncertain implications for terrestrial carbon (C) sequestration. Soil wetting from above (precipitation) results in a characteristically different pattern of pore-filling than wetting from below (groundwater), with larger, well-connected pores filling before finer pore spaces, unlike groundwater rise in which capillary forces saturate the finest pores first. Here we demonstrate that pore-scale wetting patterns interact with antecedent soil moisture conditions to alter pore-, core- and field-scale C dynamics. Drought legacy and wetting direction are perhaps more important determinants of short-term C mineralization than current soilmore » moisture content in these soils. Our results highlight that microbial access to C is not solely limited by physical protection, but also by drought or wetting-induced shifts in hydrologic connectivity. We argue that models should treat soil moisture within a three-dimensional framework emphasizing hydrologic conduits for C and resource diffusion.« less

Understanding Hydraulic Fracturing: A Multi-Scale Problem

DOE PAGES

Hyman, Jeffrey De'Haven; Gimenez Martinez, Joaquin; Viswanathan, Hari S.; ...

2016-09-05

Despite the impact that hydraulic fracturing has had on the energy sector, the physical mechanisms that control its efficiency and environmental impacts remain poorly understood in part because the length scales involved range from nano-meters to kilo-meters. We characterize flow and transport in shale formations across and between these scales using integrated computational, theoretical, and experimental efforts. At the field scale, we use discrete fracture network modeling to simulate production at a well site whose fracture network is based on a site characterization of a shale formation. At the core scale, we use triaxial fracture experiments and a finite-element discrete-elementmore » fracture propagation model with a coupled fluid solver to study dynamic crack propagation in low permeability shale. We use lattice Boltzmann pore-scale simulations and microfluidic experiments in both synthetic and real micromodels to study pore-scale flow phenomenon such as multiphase flow and mixing. A mechanistic description and integration of these multiple scales is required for accurate predictions of production and the eventual optimization of hydrocarbon extraction from unconventional reservoirs.« less

Macroscopic modeling of heat and water vapor transfer with phase change in dry snow based on an upscaling method: Influence of air convection

NASA Astrophysics Data System (ADS)

Calonne, N.; Geindreau, C.; Flin, F.

2015-12-01

At the microscopic scale, i.e., pore scale, dry snow metamorphism is mainly driven by the heat and water vapor transfer and the sublimation-deposition process at the ice-air interface. Up to now, the description of these phenomena at the macroscopic scale, i.e., snow layer scale, in the snowpack models has been proposed in a phenomenological way. Here we used an upscaling method, namely, the homogenization of multiple-scale expansions, to derive theoretically the macroscopic equivalent modeling of heat and vapor transfer through a snow layer from the physics at the pore scale. The physical phenomena under consideration are steady state air flow, heat transfer by conduction and convection, water vapor transfer by diffusion and convection, and phase change (sublimation and deposition). We derived three different macroscopic models depending on the intensity of the air flow considered at the pore scale, i.e., on the order of magnitude of the pore Reynolds number and the Péclet numbers: (A) pure diffusion, (B) diffusion and moderate convection (Darcy's law), and (C) strong convection (nonlinear flow). The formulation of the models includes the exact expression of the macroscopic properties (effective thermal conductivity, effective vapor diffusion coefficient, and intrinsic permeability) and of the macroscopic source terms of heat and vapor arising from the phase change at the pore scale. Such definitions can be used to compute macroscopic snow properties from 3-D descriptions of snow microstructures. Finally, we illustrated the precision and the robustness of the proposed macroscopic models through 2-D numerical simulations.

Pore-Scale Investigation on Stress-Dependent Characteristics of Granular Packs and Their Impact on Multiphase Fluid Distribution

NASA Astrophysics Data System (ADS)

Torrealba, V.; Karpyn, Z.; Yoon, H.; Hart, D. B.; Klise, K. A.

2013-12-01

The pore-scale dynamics that govern multiphase flow under variable stress conditions are not well understood. This lack of fundamental understanding limits our ability to quantitatively predict multiphase flow and fluid distributions in natural geologic systems. In this research, we focus on pore-scale, single and multiphase flow properties that impact displacement mechanisms and residual trapping of non-wetting phase under varying stress conditions. X-ray micro-tomography is used to image pore structures and distribution of wetting and non-wetting fluids in water-wet synthetic granular packs, under dynamic load. Micro-tomography images are also used to determine structural features such as medial axis, surface area, and pore body and throat distribution; while the corresponding transport properties are determined from Lattice-Boltzmann simulations performed on lattice replicas of the imaged specimens. Results are used to investigate how inter-granular deformation mechanisms affect fluid displacement and residual trapping at the pore-scale. This will improve our understanding of the dynamic interaction of mechanical deformation and fluid flow during enhanced oil recovery and geologic CO2 sequestration. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

Pores-scale hydrodynamics in a progressively bio-clogged three-dimensional porous medium: 3D particle tracking experiments and stochastic transport modelling

NASA Astrophysics Data System (ADS)

Morales, V. L.; Carrel, M.; Dentz, M.; Derlon, N.; Morgenroth, E.; Holzner, M.

2017-12-01

Biofilms are ubiquitous bacterial communities growing in various porous media including soils, trickling and sand filters and are relevant for applications such as the degradation of pollutants for bioremediation, waste water or drinking water production purposes. By their development, biofilms dynamically change the structure of porous media, increasing the heterogeneity of the pore network and the non-Fickian or anomalous dispersion. In this work, we use an experimental approach to investigate the influence of biofilm growth on pore scale hydrodynamics and transport processes and propose a correlated continuous time random walk model capturing these observations. We perform three-dimensional particle tracking velocimetry at four different time points from 0 to 48 hours of biofilm growth. The biofilm growth notably impacts pore-scale hydrodynamics, as shown by strong increase of the average velocity and in tailing of Lagrangian velocity probability density functions. Additionally, the spatial correlation length of the flow increases substantially. This points at the formation of preferential flow pathways and stagnation zones, which ultimately leads to an increase of anomalous transport in the porous media considered, characterized by non-Fickian scaling of mean-squared displacements and non-Gaussian distributions of the displacement probability density functions. A gamma distribution provides a remarkable approximation of the bulk and the high tail of the Lagrangian pore-scale velocity magnitude, indicating a transition from a parallel pore arrangement towards a more serial one. Finally, a correlated continuous time random walk based on a stochastic relation velocity model accurately reproduces the observations and could be used to predict transport beyond the time scales accessible to the experiment.

Dewetting of silica surfaces upon reactions with supercritical CO2 and brine: pore-scale studies in micromodels.

PubMed

Kim, Yongman; Wan, Jiamin; Kneafsey, Timothy J; Tokunaga, Tetsu K

2012-04-03

Wettability of reservoir minerals and rocks is a critical factor controlling CO(2) mobility, residual trapping, and safe-storage in geologic carbon sequestration, and currently is the factor imparting the greatest uncertainty in predicting capillary behavior in porous media. Very little information on wettability in supercritical CO(2) (scCO(2))-mineral-brine systems is available. We studied pore-scale wettability and wettability alteration in scCO(2)-silica-brine systems using engineered micromodels (transparent pore networks), at 8.5 MPa and 45 °C, over a wide range of NaCl concentrations up to 5.0 M. Dewetting of silica surfaces upon reactions with scCO(2) was observed through water film thinning, water droplet formation, and contact angle increases within single pores. The brine contact angles increased from initial values near 0° up to 80° with larger increases under higher ionic strength conditions. Given the abundance of silica surfaces in reservoirs and caprocks, these results indicate that CO(2) induced dewetting may have important consequences on CO(2) sequestration including reducing capillary entry pressure, and altering quantities of CO(2) residual trapping, relative permeability, and caprock integrity.

Investigating Darcy-scale assumptions by means of a multiphysics algorithm

NASA Astrophysics Data System (ADS)

Tomin, Pavel; Lunati, Ivan

2016-09-01

Multiphysics (or hybrid) algorithms, which couple Darcy and pore-scale descriptions of flow through porous media in a single numerical framework, are usually employed to decrease the computational cost of full pore-scale simulations or to increase the accuracy of pure Darcy-scale simulations when a simple macroscopic description breaks down. Despite the massive increase in available computational power, the application of these techniques remains limited to core-size problems and upscaling remains crucial for practical large-scale applications. In this context, the Hybrid Multiscale Finite Volume (HMsFV) method, which constructs the macroscopic (Darcy-scale) problem directly by numerical averaging of pore-scale flow, offers not only a flexible framework to efficiently deal with multiphysics problems, but also a tool to investigate the assumptions used to derive macroscopic models and to better understand the relationship between pore-scale quantities and the corresponding macroscale variables. Indeed, by direct comparison of the multiphysics solution with a reference pore-scale simulation, we can assess the validity of the closure assumptions inherent to the multiphysics algorithm and infer the consequences for macroscopic models at the Darcy scale. We show that the definition of the scale ratio based on the geometric properties of the porous medium is well justified only for single-phase flow, whereas in case of unstable multiphase flow the nonlinear interplay between different forces creates complex fluid patterns characterized by new spatial scales, which emerge dynamically and weaken the scale-separation assumption. In general, the multiphysics solution proves very robust even when the characteristic size of the fluid-distribution patterns is comparable with the observation length, provided that all relevant physical processes affecting the fluid distribution are considered. This suggests that macroscopic constitutive relationships (e.g., the relative permeability) should account for the fact that they depend not only on the saturation but also on the actual characteristics of the fluid distribution.

Topological characteristics underpin intermittency and anomalous transport behavior in soil-like porous media

NASA Astrophysics Data System (ADS)

Holzner, M.; Morales, V.; Willmann, M.; Jerjen, I.; Kaufmann, R.; Dentz, M.

2016-12-01

Continuum models of porous media are based on the validity of the Darcy equation for fluid and Fick's law for scalar fluxes on a representative elementary volume. Fluctuations of pore-scale flow and scalar transport are averaged out and represented in terms of effective parameters such as hydrodynamic dispersion. However, the intermittent behavior of pore-scale flow impacts on the nature of particle and scalar transport, and it determines the way dissolved substances mix and react. The understanding of the origin of these processes is of both fundamental and practical importance in applications ranging from reactive transport in groundwater flow to diffusion in fuel cells or biological systems. A central issue in porous medium flow is therefore to relate intermittent behavior of Lagrangian velocity at pore scale imposed by the complex pore network geometry to transport properties at larger scales. Lagrangian measurements in porous systems are nonetheless scarce and most experimental techniques do not provide access to all three velocity components. In this contribution we report 3D measurements of Lagrangian velocity in soil-like porous media. We complement these measurements with detailed X-ray scans of the pore network. We find sharp velocity transitions close to pore throats, and low flow variability in the pore bodies, which gives rise to stretched exponential Lagrangian velocity and acceleration distributions characterized by a sharp peak at low velocity and a superlinear evolution of particle dispersion. We demonstrate that porosity and pore size distribution alone cannot explain the observed features of the flow. Rather, anomalous transport is better interpreted in terms of how pores of various geometries are interconnected. We reproduce the main observations using a continuous-time random walk (CTRW) model revealing the main features that control the system and showing the potential of this simple model to capture transport in complex geometries.

Comparison of fouling characteristics in different pore-sized submerged ceramic membrane bioreactors.

PubMed

Jin, Le; Ong, Say Leong; Ng, How Yong

2010-12-01

Membrane fouling, the key disadvantage that inevitably occurs continuously in the membrane bioreactor (MBR), baffles the wide-scale application of MBR. Ceramic membrane, which possesses high chemical and thermal resistance, has seldom been used in MBR to treat municipal wastewater. Four ceramic membranes with the same materials but different pore sizes, ranging from 80 to 300 nm, were studied in parallel using four lab-scale submerged MBRs (i.e., one type of ceramic membrane in one MBR). Total COD and ammonia nitrogen removal efficiencies were observed to be consistently above 94.5 and 98%, respectively, in all submerged ceramic membrane bioreactors. The experimental results showed that fouling was mainly affected by membrane's microstructure, surface roughness and pore sizes. Ceramic membrane with the roughest surface and biggest pore size (300 nm) had the highest fouling potential with respect to the TMP profile. The 80 nm membrane with a smoother surface and relatively uniform smaller pore openings experienced least membrane fouling with respect to TMP increase. The effects of the molecular weight distribution, particle size distribution and other biomass characteristics such as extracellular polymeric substances, zeta potential and capillary suction time, were also investigated in this study. Results showed that no significant differences of these attributes were observed. These observations indicate that the membrane surface properties are the dominant factors leading to different fouling potential in this study. Copyright © 2010 Elsevier Ltd. All rights reserved.

Hydraulic conductivity of variably saturated porous media: Film and corner flow in angular pore space

NASA Astrophysics Data System (ADS)

Tuller, Markus; Or, Dani

2001-05-01

Many models for hydraulic conductivity of partially saturated porous media rely on oversimplified representation of the pore space as a bundle of cylindrical capillaries and disregard flow in liquid films. Recent progress in modeling liquid behavior in angular pores of partially saturated porous media offers an alternative framework. We assume that equilibrium liquid-vapor interfaces provide well-defined and stable boundaries for slow laminar film and corner flow regimes in pore space comprised of angular pores connected to slit-shaped spaces. Knowledge of liquid configuration in the assumed geometry facilitates calculation of average liquid velocities in films and corners and enables derivation of pore-scale hydraulic conductivity as a function of matric potential. The pore-scale model is statistically upscaled to represent hydraulic conductivity for a sample of porous medium. Model parameters for the analytical sample-scale expressions are estimated from measured liquid retention data and other measurable medium properties. Model calculations illustrate the important role of film flow, whose contribution dominates capillary flow (in full pores and corners) at relatively high matric potentials (approximately -100 to -300 J kg-1, or -1 to 3 bars). The crossover region between film and capillary flow is marked by a significant change in the slope of the hydraulic conductivity function as often observed in measurements. Model predictions are compared with the widely applied van Genuchten-Mualem model and yield reasonable agreement with measured retention and hydraulic conductivity data over a wide range of soil textural classes.

One Hundred Ways to be Non-Fickian - A Rigorous Multi-Variate Statistical Analysis of Pore-Scale Transport

NASA Astrophysics Data System (ADS)

Most, Sebastian; Nowak, Wolfgang; Bijeljic, Branko

2015-04-01

Fickian transport in groundwater flow is the exception rather than the rule. Transport in porous media is frequently simulated via particle methods (i.e. particle tracking random walk (PTRW) or continuous time random walk (CTRW)). These methods formulate transport as a stochastic process of particle position increments. At the pore scale, geometry and micro-heterogeneities prohibit the commonly made assumption of independent and normally distributed increments to represent dispersion. Many recent particle methods seek to loosen this assumption. Hence, it is important to get a better understanding of the processes at pore scale. For our analysis we track the positions of 10.000 particles migrating through the pore space over time. The data we use come from micro CT scans of a homogeneous sandstone and encompass about 10 grain sizes. Based on those images we discretize the pore structure and simulate flow at the pore scale based on the Navier-Stokes equation. This flow field realistically describes flow inside the pore space and we do not need to add artificial dispersion during the transport simulation. Next, we use particle tracking random walk and simulate pore-scale transport. Finally, we use the obtained particle trajectories to do a multivariate statistical analysis of the particle motion at the pore scale. Our analysis is based on copulas. Every multivariate joint distribution is a combination of its univariate marginal distributions. The copula represents the dependence structure of those univariate marginals and is therefore useful to observe correlation and non-Gaussian interactions (i.e. non-Fickian transport). The first goal of this analysis is to better understand the validity regions of commonly made assumptions. We are investigating three different transport distances: 1) The distance where the statistical dependence between particle increments can be modelled as an order-one Markov process. This would be the Markovian distance for the process, where the validity of yet-unexplored non-Gaussian-but-Markovian random walks start. 2) The distance where bivariate statistical dependence simplifies to a multi-Gaussian dependence based on simple linear correlation (validity of correlated PTRW/CTRW). 3) The distance of complete statistical independence (validity of classical PTRW/CTRW). The second objective is to reveal characteristic dependencies influencing transport the most. Those dependencies can be very complex. Copulas are highly capable of representing linear dependence as well as non-linear dependence. With that tool we are able to detect persistent characteristics dominating transport even across different scales. The results derived from our experimental data set suggest that there are many more non-Fickian aspects of pore-scale transport than the univariate statistics of longitudinal displacements. Non-Fickianity can also be found in transverse displacements, and in the relations between increments at different time steps. Also, the found dependence is non-linear (i.e. beyond simple correlation) and persists over long distances. Thus, our results strongly support the further refinement of techniques like correlated PTRW or correlated CTRW towards non-linear statistical relations.

Saturation-dependent solute dispersivity in porous media: Pore-scale processes

NASA Astrophysics Data System (ADS)

Raoof, A.; Hassanizadeh, S. M.

2013-04-01

It is known that in variably saturated porous media, dispersion coefficient depends on Darcy velocity and water saturation. In one-dimensional flow, it is commonly assumed that the dispersion coefficient is a linear function of velocity. The coefficient of proportionality, called the dispersivity, is considered to depend on saturation. However, there is not much known about its dependence on saturation. In this study, we investigate, using a pore network model, how the longitudinal dispersivity varies nonlinearly with saturation. We schematize the porous medium as a network of pore bodies and pore throats with finite volumes. The pore space is modeled using the multidirectional pore-network concept, which allows for a distribution of pore coordination numbers. This topological property together with the distribution of pore sizes are used to mimic the microstructure of real porous media. The dispersivity is calculated by solving the mass balance equations for solute concentration in all network elements and averaging the concentrations over a large number of pores. We have introduced a new formulation of solute transport within pore space, where we account for different compartments of residual water within drained pores. This formulation makes it possible to capture the effect of limited mixing due to partial filling of the pores under variably saturated conditions. We found that dispersivity increases with the decrease in saturation, it reaches a maximum value, and then decreases with further decrease in saturation. To show the capability of our formulation to properly capture the effect of saturation on solute dispersion, we applied it to model the results of a reported experimental study.

Experimental evidence of the role of pores on movement and distribution of bacteria in soil

NASA Astrophysics Data System (ADS)

Kravchenko, Alexandra N.; Rose, Joan B.; Marsh, Terence L.; Guber, Andrey K.

2014-05-01

It has been generally recognized that micro-scale heterogeneity in soil environments can have a substantial effect on movement, fate, and survival of soil microorganisms. However, only recently the development of tools for micro-scale soil analyses, including X-ray computed micro-tomography (μ-CT), enabled quantitative analyses of these effects. The long-term goal of our work is to explore how differences in micro-scale characteristics of pore structures influence movement, spatial distribution patterns, and activities of soil microorganisms. Using X-ray μ-CT we found that differences in land use and management practices lead to development of contrasting patterns in pore size-distributions within intact soil aggregates. Then our experiments with Escherichia coli added to intact soil aggregates demonstrated that the differences in pore structures can lead to substantial differences in bacteria redistribution and movement within the aggregates. Specifically, we observed more uniform E.coli redistribution in aggregates with homogeneously spread pores, while heterogeneous pore structures resulted in heterogeneous E.coli patterns. Water flow driven by capillary forces through intact aggregate pores appeared to be the main contributor to the movement patterns of the introduced bacteria. Influence of pore structure on E.coli distribution within the aggregates further continued after the aggregates were subjected to saturated water flow. E. coli's resumed movement with saturated water flow and subsequent redistribution within the soil matrix was influenced by porosity, abundance of medium and large pores, pore tortuosity, and flow rates, indicating that greater flow accompanied by less convoluted pores facilitated E. coli transport within the intra-aggregate space. We also found that intra-aggregate heterogeneity of pore structures can have an effect on spatial distribution patterns of indigenous microbial populations. Preliminary analysis showed that in aggregates from an organic agricultural system with cover crops, characterized by greater intra-aggregate pore heterogeneity, bacteria of Actinobacteria and Firmicutes groups were more abundant in presence of large as compared to small pores. In contrast, no differences were observed in the aggregates from conventionally managed soil, overall characterized by homogeneous intra-aggregate pore patterns. Further research efforts are being directed towards quantification of the pore structure effects on activities and community composition of soil microorganisms.

Confinement-Driven Phase Separation of Quantum Liquid Mixtures

NASA Astrophysics Data System (ADS)

Prisk, T. R.; Pantalei, C.; Kaiser, H.; Sokol, P. E.

2012-08-01

We report small-angle neutron scattering studies of liquid helium mixtures confined in Mobil Crystalline Material-41 (MCM-41), a porous silica glass with narrow cylindrical nanopores (d=3.4nm). MCM-41 is an ideal model adsorbent for fundamental studies of gas sorption in porous media because its monodisperse pores are arranged in a 2D triangular lattice. The small-angle scattering consists of a series of diffraction peaks whose intensities are determined by how the imbibed liquid fills the pores. Pure He4 adsorbed in the pores show classic, layer-by-layer film growth as a function of pore filling, leaving the long range symmetry of the system intact. In contrast, the adsorption of He3-He4 mixtures produces a structure incommensurate with the pore lattice. Neither capillary condensation nor preferential adsorption of one helium isotope to the pore walls can provide the symmetry-breaking mechanism. The scattering is consistent with the formation of randomly distributed liquid-liquid microdomains ˜2.3nm in size, providing evidence that confinement in a nanometer scale capillary can drive local phase separation in quantum liquid mixtures.

Dynamic bulk and shear moduli due to grain-scale local fluid flow in fluid-saturated cracked poroelastic rocks: Theoretical model

NASA Astrophysics Data System (ADS)

Song, Yongjia; Hu, Hengshan; Rudnicki, John W.

2016-07-01

Grain-scale local fluid flow is an important loss mechanism for attenuating waves in cracked fluid-saturated poroelastic rocks. In this study, a dynamic elastic modulus model is developed to quantify local flow effect on wave attenuation and velocity dispersion in porous isotropic rocks. The Eshelby transform technique, inclusion-based effective medium model (the Mori-Tanaka scheme), fluid dynamics and mass conservation principle are combined to analyze pore-fluid pressure relaxation and its influences on overall elastic properties. The derivation gives fully analytic, frequency-dependent effective bulk and shear moduli of a fluid-saturated porous rock. It is shown that the derived bulk and shear moduli rigorously satisfy the Biot-Gassmann relationship of poroelasticity in the low-frequency limit, while they are consistent with isolated-pore effective medium theory in the high-frequency limit. In particular, a simplified model is proposed to quantify the squirt-flow dispersion for frequencies lower than stiff-pore relaxation frequency. The main advantage of the proposed model over previous models is its ability to predict the dispersion due to squirt flow between pores and cracks with distributed aspect ratio instead of flow in a simply conceptual double-porosity structure. Independent input parameters include pore aspect ratio distribution, fluid bulk modulus and viscosity, and bulk and shear moduli of the solid grain. Physical assumptions made in this model include (1) pores are inter-connected and (2) crack thickness is smaller than the viscous skin depth. This study is restricted to linear elastic, well-consolidated granular rocks.

Pore-scale modeling of capillary trapping in water-wet porous media: A new cooperative pore-body filling model

NASA Astrophysics Data System (ADS)

Ruspini, L. C.; Farokhpoor, R.; Øren, P. E.

2017-10-01

We present a pore-network model study of capillary trapping in water-wet porous media. The amount and distribution of trapped non-wetting phase is determined by the competition between two trapping mechanisms - snap-off and cooperative pore-body filling. We develop a new model to describe the pore-body filling mechanism in geologically realistic pore-networks. The model accounts for the geometrical characteristics of the pore, the spatial location of the connecting throats and the local fluid topology at the time of the displacement. We validate the model by comparing computed capillary trapping curves with published data for four different water-wet rocks. Computations are performed on pore-networks extracted from micro-CT images and process-based reconstructions of the actual rocks used in the experiments. Compared with commonly used stochastic models, the new model describes more accurately the experimental measurements, especially for well connected porous systems where trapping is controlled by subtleties of the pore structure. The new model successfully predicts relative permeabilities and residual saturation for Bentheimer sandstone using in-situ measured contact angles as input to the simulations. The simulated trapped cluster size distributions are compared with predictions from percolation theory.

Atomistic and continuum scale modeling of functionalized graphyne membranes for water desalination.

PubMed

Raju, Muralikrishna; Govindaraju, Pavan B; van Duin, Adri C T; Ihme, Matthias

2018-02-22

Recent theoretical and experimental studies reported ultra-high water permeability and salt rejection in nanoporous single-layer graphene. However, creating and controlling the size and distribution of nanometer-scale pores pose significant challenges to application of these membranes for water desalination. Graphyne and hydrogenated graphyne have tremendous potential as ultra-permeable membranes for desalination and wastewater reclamation due to their uniform pore-distribution, atomic thickness and mechano-chemical stability. Using molecular dynamics (MD) simulations and upscale continuum analysis, the desalination performance of bare and hydrogenated α-graphyne and γ-{2,3,4}-graphyne membranes is evaluated as a function of pore size, pore geometry, chemical functionalization and applied pressure. MD simulations show that pores ranging from 20 to 50 Å 2 reject in excess of 90% of the ions for pressures up to 1 GPa. Water permeability is found to range up to 85 L cm -2 day -1 MPa -1 , which is up to three orders of magnitude larger than commercial seawater reverse osmosis (RO) membranes and up to ten times that of nanoporous graphene. Pore chemistry, functionalization and geometry are shown to play a critical role in modulating the water flux, and these observations are explained by water velocity, density, and energy barriers in the pores. The atomistic scale investigations are complemented by upscale continuum analysis to examine the performance of these membranes in application to cross-flow RO systems. This upscale analysis, however, shows that the significant increase in permeability, observed from MD simulations, does not fully translate to current RO systems due to transport limitations. Nevertheless, upscale calculations predict that the higher permeability of graphyne membranes would allow up to six times higher permeate recovery or up to 6% less energy consumption as compared to thin-film composite membranes at currently accessible operating conditions. Significantly higher energy savings and permeate recovery can be achieved if higher feed-flow rates can be realized.

EVALUATION AND ANALYSIS OF MICROSCALE FLOW AND TRANSPORT DURING REMEDIATION

EPA Science Inventory

The design of in-situ remediation is currently based on a description at the macroscopic scale. Phenomena at the pore and pore-network scales are typically lumped in terms of averaged quantities, using empirical or ad hoc expressions. These models cannot address fundamental rem...

Multiscale modeling of shock wave localization in porous energetic material

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wood, M. A.; Kittell, D. E.; Yarrington, C. D.

Shock wave interactions with defects, such as pores, are known to play a key role in the chemical initiation of energetic materials. The shock response of hexanitrostilbene is studied through a combination of large-scale reactive molecular dynamics and mesoscale hydrodynamic simulations. In order to extend our simulation capability at the mesoscale to include weak shock conditions (< 6 GPa), atomistic simulations of pore collapse are used here to define a strain-rate-dependent strength model. Comparing these simulation methods allows us to impose physically reasonable constraints on the mesoscale model parameters. In doing so, we have been able to study shock wavesmore » interacting with pores as a function of this viscoplastic material response. Finally, we find that the pore collapse behavior of weak shocks is characteristically different than that of strong shocks.« less

Multiscale modeling of shock wave localization in porous energetic material

DOE PAGES

Wood, M. A.; Kittell, D. E.; Yarrington, C. D.; ...

2018-01-30

Shock wave interactions with defects, such as pores, are known to play a key role in the chemical initiation of energetic materials. The shock response of hexanitrostilbene is studied through a combination of large-scale reactive molecular dynamics and mesoscale hydrodynamic simulations. In order to extend our simulation capability at the mesoscale to include weak shock conditions (< 6 GPa), atomistic simulations of pore collapse are used here to define a strain-rate-dependent strength model. Comparing these simulation methods allows us to impose physically reasonable constraints on the mesoscale model parameters. In doing so, we have been able to study shock wavesmore » interacting with pores as a function of this viscoplastic material response. Finally, we find that the pore collapse behavior of weak shocks is characteristically different than that of strong shocks.« less

Imaging of forced-imbibition in carbonate rocks using synchrotron X-ray micro-tomography

NASA Astrophysics Data System (ADS)

Singh, K.; Menke, H. P.; Andrew, M. G.; Lin, Q.; Saif, T.; Al-Khulaifi, Y.; Reynolds, C. A.; Bijeljic, B.; Rau, C.; Blunt, M. J.

2016-12-01

We have investigated the pore-scale behavior of brine-oil systems and oil trapping during forced-imbibition in a water-wet carbonate rock in a capillary-dominated flow regime at reservoir pressure conditions. To capture the dynamics of the brine-oil front progression and snap-off process, real-time tomograms with a time resolution of 38 s (24 s for imaging and 14 s for recording the data) and a spatial resolution of 3.28 µm were acquired at Diamond Light Source (UK). The data were first analyzed at global scale (complete imaged rock) for overall front behavior. From the saturation profiles, we obtain the location of the tail of the desaturation front that progresses with a velocity of 13 µm/min. This velocity is smaller than average flow velocity 16.88 µm/min, which explains why it needs slightly more than 1 pore volume of brine injection to reach the residual saturation of oil in a water-wet rock. The data were further analyzed at local scale to investigate the pore-scale mechanisms of oil trapping during brine flooding. We isolated various trapping events which resulted in the creation of discrete oil ganglia occupying one to several pore bodies. We perform pore-scale curvature analysis of brine-oil interfaces to obtain local capillary pressure that will be related to the shape and the size of throats in which ganglia were trapped.

Capillary pressure-saturation relationships for porous granular materials: Pore morphology method vs. pore unit assembly method

NASA Astrophysics Data System (ADS)

Sweijen, Thomas; Aslannejad, Hamed; Hassanizadeh, S. Majid

2017-09-01

In studies of two-phase flow in complex porous media it is often desirable to have an estimation of the capillary pressure-saturation curve prior to measurements. Therefore, we compare in this research the capability of three pore-scale approaches in reproducing experimentally measured capillary pressure-saturation curves. To do so, we have generated 12 packings of spheres that are representative of four different glass-bead packings and eight different sand packings, for which we have found experimental data on the capillary pressure-saturation curve in the literature. In generating the packings, we matched the particle size distributions and porosity values of the granular materials. We have used three different pore-scale approaches for generating the capillary pressure-saturation curves of each packing: i) the Pore Unit Assembly (PUA) method in combination with the Mayer and Stowe-Princen (MS-P) approximation for estimating the entry pressures of pore throats, ii) the PUA method in combination with the hemisphere approximation, and iii) the Pore Morphology Method (PMM) in combination with the hemisphere approximation. The three approaches were also used to produce capillary pressure-saturation curves for the coating layer of paper, used in inkjet printing. Curves for such layers are extremely difficult to determine experimentally, due to their very small thickness and the presence of extremely small pores (less than one micrometer in size). Results indicate that the PMM and PUA-hemisphere method give similar capillary pressure-saturation curves, because both methods rely on a hemisphere to represent the air-water interface. The ability of the hemisphere approximation and the MS-P approximation to reproduce correct capillary pressure seems to depend on the type of particle size distribution, with the hemisphere approximation working well for narrowly distributed granular materials.

Micro-PIV Study of Supercritical CO2-Water Interactions in Porous Micromodels

NASA Astrophysics Data System (ADS)

Kazemifar, Farzan; Blois, Gianluca; Christensen, Kenneth T.

2015-11-01

Multiphase flow of immiscible fluids in porous media is encountered in numerous natural systems and engineering applications such as enhanced oil recovery (EOR), and CO2 sequestration among others. Geological sequestration of CO2 in saline aquifers has emerged as a viable option for reducing CO2 emissions, and thus it has been the subject of numerous studies in recent years. A key objective is improving the accuracy of numerical models used for field-scale simulations by incorporation/better representation of the pore-scale flow physics. This necessitates experimental data for developing, testing and validating such models. We have studied drainage and imbibition processes in a homogeneous, two-dimensional porous micromodel with CO2 and water at reservoir-relevant conditions. Microscopic particle image velocimetry (micro-PIV) technique was applied to obtain spatially- and temporally-resolved velocity vector fields in the aqueous phase. The results provide new insight into the flow processes at the pore scale.

Reversible Self-Actuated Thermo-Responsive Pore Membrane

PubMed Central

Park, Younggeun; Gutierrez, Maria Paz; Lee, Luke P.

2016-01-01

Smart membranes, which can selectively control the transfer of light, air, humidity and temperature, are important to achieve indoor climate regulation. Even though reversible self-actuation of smart membranes is desirable in large-scale, reversible self-regulation remains challenging. Specifically, reversible 100% opening/closing of pore actuation showing accurate responsiveness, reproducibility and structural flexibility, including uniform structure assembly, is currently very difficult. Here, we report a reversible, thermo-responsive self-activated pore membrane that achieves opening and closing of pores. The reversible, self-actuated thermo-responsive pore membrane was fabricated with hybrid materials of poly (N-isopropylacrylamide), (PNIPAM) within polytetrafluoroethylene (PTFE) to form a multi-dimensional pore array. Using Multiphysics simulation of heat transfer and structural mechanics based on finite element analysis, we demonstrated that pore opening and closing dynamics can be self-activated at environmentally relevant temperatures. Temperature cycle characterizations of the pore structure revealed 100% opening ratio at T = 40 °C and 0% opening ratio at T = 20 °C. The flexibility of the membrane showed an accurate temperature-responsive function at a maximum bending angle of 45°. Addressing the importance of self-regulation, this reversible self-actuated thermo-responsive pore membrane will advance the development of future large-scale smart membranes needed for sustainable indoor climate control. PMID:27991563

Reversible Self-Actuated Thermo-Responsive Pore Membrane

NASA Astrophysics Data System (ADS)

Park, Younggeun; Gutierrez, Maria Paz; Lee, Luke P.

2016-12-01

Smart membranes, which can selectively control the transfer of light, air, humidity and temperature, are important to achieve indoor climate regulation. Even though reversible self-actuation of smart membranes is desirable in large-scale, reversible self-regulation remains challenging. Specifically, reversible 100% opening/closing of pore actuation showing accurate responsiveness, reproducibility and structural flexibility, including uniform structure assembly, is currently very difficult. Here, we report a reversible, thermo-responsive self-activated pore membrane that achieves opening and closing of pores. The reversible, self-actuated thermo-responsive pore membrane was fabricated with hybrid materials of poly (N-isopropylacrylamide), (PNIPAM) within polytetrafluoroethylene (PTFE) to form a multi-dimensional pore array. Using Multiphysics simulation of heat transfer and structural mechanics based on finite element analysis, we demonstrated that pore opening and closing dynamics can be self-activated at environmentally relevant temperatures. Temperature cycle characterizations of the pore structure revealed 100% opening ratio at T = 40 °C and 0% opening ratio at T = 20 °C. The flexibility of the membrane showed an accurate temperature-responsive function at a maximum bending angle of 45°. Addressing the importance of self-regulation, this reversible self-actuated thermo-responsive pore membrane will advance the development of future large-scale smart membranes needed for sustainable indoor climate control.

A CSF-SPH method for simulating drainage and imbibition at pore-scale resolution while tracking interfacial areas

NASA Astrophysics Data System (ADS)

Sivanesapillai, Rakulan; Falkner, Nadine; Hartmaier, Alexander; Steeb, Holger

2016-09-01

We present a conservative smoothed particle hydrodynamics (SPH) model to study the flow of multiple, immiscible fluid phases in porous media using direct pore-scale simulations. Particular focus is put on continuously tracking the evolution of interfacial areas, which are considered to be important morphological quantities affecting multiphase transport in porous media. In addition to solving the Navier-Stokes equations, the model accounts for the effects of capillarity at interfaces and contact lines. This is done by means of incorporating the governing interfacial mass and momentum balances using the continuum surface force (CSF) method, thus rendering model calibration routines unnecessary and minimizing the set of constitutive and kinematic assumptions. We address the application of boundary conditions at rigid solid surfaces and study the predictive capability of the model as well as optimal choices for numerical parameters using an extensive model validation procedure. We demonstrate the applicability of the model to simulate multiphase flows involving partial wettability, dynamic effects, large density ratios (up to 1000), large viscosity ratios (up to 100), as well as fragmentation and coalescence of fluid phases. The model is used to study the evolution of fluid-fluid interfacial areas during saturation-controlled primary drainage and main imbibition of heterogeneous pore spaces at low capillary numbers. A variety of pore-scale effects, such as wetting phase entrapment and fragmentation due to snap-off, are observed. Specific fluid-fluid interfacial area is observed to monotonically increase during primary drainage and hysteretic effects are apparent during main imbibition.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, Li; He, YaLing; Tao, Wen -Quan

The electrode of a vanadium redox flow battery generally is a carbon fibre-based porous medium, in which important physicochemical processes occur. In this work, pore-scale simulations are performed to study complex multiphase flow and reactive transport in the electrode by using the lattice Boltzmann method (LBM). Four hundred fibrous electrodes with different fibre diameters and porosities are reconstructed. Both the permeability and diffusivity of the reconstructed electrodes are predicted and compared with empirical relationships in the literature. Reactive surface area of the electrodes is also evaluated and it is found that existing empirical relationship overestimates the reactive surface under lowermore » porosities. Further, a pore-scale electrochemical reaction model is developed to study the effects of fibre diameter and porosity on electrolyte flow, V II/V III transport, and electrochemical reaction at the electrolyte-fibre surface. Finally, evolution of bubble cluster generated by the side reaction is studied by adopting a LB multiphase flow model. Effects of porosity, fibre diameter, gas saturation and solid surface wettability on average bubble diameter and reduction of reactive surface area due to coverage of bubbles on solid surface are investigated in detail. It is found that gas coverage ratio is always lower than that adopted in the continuum model in the literature. Furthermore, the current pore-scale studies successfully reveal the complex multiphase flow and reactive transport processes in the electrode, and the simulation results can be further upscaled to improve the accuracy of the current continuum-scale models.« less

Tunable acoustic absorbers with periodical micro-perforations having varying pore shapes

NASA Astrophysics Data System (ADS)

Ren, Shuwei; Liu, Xuewei; Gong, Junqing; Tang, Yufan; Xin, Fengxian; Huang, Lixi; Lu, Tian Jian

2017-11-01

Circular pores with sub-millimeter diameters have been widely used to construct micro-perforated panels (MPPs), the acoustical performance of which can be predicted well using the Maa theory (MAA D.-Y., J. Acoust. Soc. Am., 104 (1998) 2861). We present a tunable MPP absorber with periodically arranged cylindrical pores, with their cross-sectional shapes systematically altered around the circle while maintaining their cross-sectional areas unchanged. Numerical analyses based on the viscous-thermal coupled acoustical equations are utilized to investigate the tunable acoustic performance of the proposed absorbers and to reveal the underlying physical mechanisms. We demonstrate that pore morphology significantly affects the sound absorbption of MPPs by modifying the velocity field (and hence viscous dissipation) in the pores. Pore shapes featured as meso-scale circular pores accompanied with micro-scale bulges along the boundaries can lead to perfect sound absorption at relatively low frequencies. This work not only enriches the classical Maa theory on MPPs having circular perforations, but it also opens a new avenue for designing subwavelength acoustic metamaterials of superior sound absorption in target frequency ranges.

Pore-scale Modeling of CO2 Local Trapping in Heterogeneous Porous Media with Inter-granular Cements

NASA Astrophysics Data System (ADS)

Wang, D.; Li, Y.

2017-12-01

Based on pore-scale modeling of CO2/brine multiphase flow in heterogeneous porous media with inter-granular cements, we numerically analyze the effects of cement-modified pore structure on CO2 local trapping. Results indicate: 1) small pore throat is the main reason for causing CO2 local trapping in front of low-porosity layers (namely dense layers) formed by inter-granular cements; 2) in the case of the same pore throat size, the smaller particle size can increase the number of flow paths for CO2 plume and equivalently enhances local permeability, which may counteract the impediment of high capillary pressure on CO2 migration to some extent and consequently disables CO2 local capillary trapping; 3) the isolated pores by inter-granular cements can lead to dramatic reduction of CO2 saturation inside the dense layers, whereas the change of connectivity of some pores due to the cements can increase CO2 accumulation in front of the dense layers by lowering the displacement area of CO2 plume.

X-ray CT analysis of pore structure in sand

NASA Astrophysics Data System (ADS)

Mukunoki, Toshifumi; Miyata, Yoshihisa; Mikami, Kazuaki; Shiota, Erika

2016-06-01

The development of microfocused X-ray computed tomography (CT) devices enables digital imaging analysis at the pore scale. The applications of these devices are diverse in soil mechanics, geotechnical and geoenvironmental engineering, petroleum engineering, and agricultural engineering. In particular, the imaging of the pore space in porous media has contributed to numerical simulations for single-phase and multiphase flows or contaminant transport through the pore structure as three-dimensional image data. These obtained results are affected by the pore diameter; therefore, it is necessary to verify the image preprocessing for the image analysis and to validate the pore diameters obtained from the CT image data. Moreover, it is meaningful to produce the physical parameters in a representative element volume (REV) and significant to define the dimension of the REV. This paper describes the underlying method of image processing and analysis and discusses the physical properties of Toyoura sand for the verification of the image analysis based on the definition of the REV. On the basis of the obtained verification results, a pore-diameter analysis can be conducted and validated by a comparison with the experimental work and image analysis. The pore diameter is deduced from Young-Laplace's law and a water retention test for the drainage process. The results from previous study and perforated-pore diameter originally proposed in this study, called the voxel-percolation method (VPM), are compared in this paper. In addition, the limitations of the REV, the definition of the pore diameter, and the effectiveness of the VPM for an assessment of the pore diameter are discussed.

A novel bio-safe phase separation process for preparing open-pore biodegradable polycaprolactone microparticles.

PubMed

Salerno, Aurelio; Domingo, Concepción

2014-09-01

Open-pore biodegradable microparticles are object of considerable interest for biomedical applications, particularly as cell and drug delivery carriers in tissue engineering and health care treatments. Furthermore, the engineering of microparticles with well definite size distribution and pore architecture by bio-safe fabrication routes is crucial to avoid the use of toxic compounds potentially harmful to cells and biological tissues. To achieve this important issue, in the present study a straightforward and bio-safe approach for fabricating porous biodegradable microparticles with controlled morphological and structural features down to the nanometer scale is developed. In particular, ethyl lactate is used as a non-toxic solvent for polycaprolactone particles fabrication via a thermal induced phase separation technique. The used approach allows achieving open-pore particles with mean particle size in the 150-250 μm range and a 3.5-7.9 m(2)/g specific surface area. Finally, the combination of thermal induced phase separation and porogen leaching techniques is employed for the first time to obtain multi-scaled porous microparticles with large external and internal pore sizes and potential improved characteristics for cell culture and tissue engineering. Samples were characterized to assess their thermal properties, morphology and crystalline structure features and textural properties. Copyright © 2014 Elsevier B.V. All rights reserved.

Pore-scale modeling of wettability effects on CO2-brine displacement during geological storage

NASA Astrophysics Data System (ADS)

Basirat, Farzad; Yang, Zhibing; Niemi, Auli

2017-11-01

Wetting properties of reservoir rocks and caprocks can vary significantly, and they strongly influence geological storage of carbon dioxide in deep saline aquifers, during which CO2 is supposed to displace the resident brine and to become permanently trapped. Fundamental understanding of the effect of wettability on CO2-brine displacement is thus important for improving storage efficiency and security. In this study, we investigate the influence of wetting properties on two-phase flow of CO2 and brine at the pore scale. A numerical model based on the phase field method is implemented to simulate the two-phase flow of CO2-brine in a realistic pore geometry. Our focus is to study the pore-scale fluid-fluid displacement mechanisms under different wetting conditions and to quantify the effect of wettability on macroscopic parameters such as residual brine saturation, capillary pressure, relative permeability, and specific interfacial area. Our simulation results confirm that both the trapped wetting phase saturation and the normalized interfacial area increase with decreasing contact angle. However, the wetting condition does not appear to influence the CO2 breakthrough time and saturation. We also show that the macroscopic capillary pressures based on the pressure difference between inlet and outlet can differ significantly from the phase averaging capillary pressures for all contact angles when the capillary number is high (log Ca > -5). This indicates that the inlet-outlet pressure difference may not be a good measure of the continuum-scale capillary pressure. In addition, the results show that the relative permeability of CO2 can be significantly lower in strongly water-wet conditions than in the intermediate-wet conditions.

Experimental and simulation studies of pore scale flow and reactive transport associated with supercritical CO2 injection into brine-filled reservoir rocks (Invited)

NASA Astrophysics Data System (ADS)

DePaolo, D. J.; Steefel, C. I.; Bourg, I. C.

2013-12-01

This talk will review recent research relating to pore scale reactive transport effects done in the context of the Department of Energy-sponsored Energy Frontier Research Center led by Lawrence Berkeley National Laboratory with several other laboratory and University partners. This Center, called the Center for Nanoscale Controls on Geologic CO2 (NCGC) has focused effort on the behavior of supercritical CO2 being injected into and/or residing as capillary trapped-bubbles in sandstone and shale, with particular emphasis on the description of nanoscale to pore scale processes that could provide the basis for advanced simulations. In general, simulation of reservoir-scale behavior of CO2 sequestration assumes a number of mostly qualitative relationships that are defensible as nominal first-order descriptions of single-fluid systems, but neglect the many complications that are associated with a two-phase or three-phase reactive system. The contrasts in properties, and the mixing behavior of scCO2 and brine provide unusual conditions for water-rock interaction, and the NCGC has investigated the underlying issues by a combination of approaches including theoretical and experimental studies of mineral nucleation and growth, experimental studies of brine films, mineral wetting properties, dissolution-precipitation rates and infiltration patterns, molecular dynamic simulations and neutron scattering experiments of fluid properties for fluid confined in nanopores, and various approaches to numerical simulation of reactive transport processes. The work to date has placed new constraints on the thickness of brine films, and also on the wetting properties of CO2 versus brine, a property that varies between minerals and with salinity, and may also change with time as a result of the reactivity of CO2-saturated brine. Mineral dissolution is dependent on reactive surface area, which can be shown to vary by a large factor for various minerals, especially when correlated with interconnected pore space. High-resolution numerical simulations of reactive transport can ultimate lead to quantitative descriptions of pore scale chemistry and flow, and examples of recent developments will be presented. However, only a limited description of the processes can realistically be treated in such simulations, and only for chemically simple systems. Whether and when more complete simulations will be achievable is yet to be determined.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wei, Chan Yi, E-mail: vicchanyiwei@hotmail.com; Ongkudon, Clarence M., E-mail: clarence@ums.edu.my; Kansil, Tamar, E-mail: tamarkansil87@gmail.com

Modern day synthesis protocols of methacrylate monolithic polymer adsorbent are based on existing polymerization blueprint without a thorough understanding of the dynamics of pore structure and formation. This has resulted in unproductiveness of polymer adsorbent consequently affecting purity and recovery of final product, productivity, retention time and cost effectiveness of the whole process. The problems magnified in monolith scaling-up where internal heat buildup resulting from external heating and high exothermic polymerization reaction was reflected in cracking of the adsorbent. We believe that through careful and precise control of the polymerization kinetics and parameters, it is possible to prepare macroporous methacrylatemore » monolithic adsorbents with controlled pore structures despite being carried out in an unstirred mould. This research involved the study of the effect of scaling-up on pore morphology of monolith, in other words, porous polymethacrylate adsorbents that were prepared via bulk free radical polymerization process by imaging the porous morphology of polymethacrylate with scanning electron microscope.« less

Comparison of Pore-scale CO2-water-glass System Wettability and Conventional Wettability Measurement on a Flat Plate for Geological CO2 Sequestration

NASA Astrophysics Data System (ADS)

Jafari, M.; Cao, S. C.; Jung, J.

2017-12-01

Goelogical CO2 sequestration (GCS) has been recently introduced as an effective method to mitigate carbon dioxide emission. CO2 from main producer sources is collected and then is injected underground formations layers to be stored for thousands to millions years. A safe and economical storage project depends on having an insight of trapping mechanisms, fluids dynamics, and interaction of fluids-rocks. Among different forces governing fluids mobility and distribution in GCS condition, capillary pressure is of importance, which, in turn, wettability (measured by contact angel (CA)) is the most controversial parameters affecting it. To explore the sources of discrepancy in the literature for CA measurement, we conducted a series of conventional captive bubble test on glass plates under high pressure condition. By introducing a shape factor, we concluded that surface imperfection can distort the results in such tests. Since the conventional methods of measuring the CA is affected by gravity and scale effect, we introduced a different technique to measure pore-scale CA inside a transparent glass microchip. Our method has the ability to consider pore sizes and simulate static and dynamics CA during dewetting and imbibition. Glass plates shows a water-wet behavior (CA 30° - 45°) by a conventional experiment consistent with literature. However, CA of miniature bubbles inside of the micromodel can have a weaker water-wet behavior (CA 55° - 69°). In a more realistic pore-scale condition, water- CO2 interface covers whole width of a pore throats. Under this condition, the receding CA, which is used for injectability and capillary breakthrough pressure, increases with decreasing pores size. On the other hand, advancing CA, which is important for residual or capillary trapping, does not show a correlation with throat sizes. Static CA measured in the pores during dewetting is lower than static CA on flat plate, but it is much higher when measured during imbibition implying weaker water-wet behavior. Pore-scale CA, which realistically represents rocks wettability behavior, shows weaker water-wet behavior than conventional measurement methods, which must be considered for safety of geological storage.

Importance of filter’s microstructure in dynamic filtration modeling of gasoline particulate filters (GPFs): Inhomogeneous porosity and pore size distribution

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gong, Jian; Stewart, Mark L.; Zelenyuk, Alla

The state-of-the-art multiscale modeling of GPFs including channel scale, wall scale, and pore scale is described. The microstructures of two GPFs were experimentally characterized. The pore size distributions of the GPFs were determined by mercury porosimetry. The porosity was measured by X-ray computed tomography (CT) and found to be inhomogeneous across the substrate wall. The significance of pore size distribution with respect to filtration performance was analyzed. The predictions of filtration efficiency were improved by including the pore size distribution in the filtration model. A dynamic heterogeneous multiscale filtration (HMF) model was utilized to simulate particulate filtration on a singlemore » channel particulate filter with realistic particulate emissions from a spark-ignition direct-injection (SIDI) gasoline engine. The dynamic evolution of filter’s microstructure and macroscopic filtration characteristics including mass- and number-based filtration efficiencies and pressure drop were predicted and discussed. The microstructure of the GPF substrate including inhomogeneous porosity and pore size distribution is found to significantly influence local particulate deposition inside the substrate and macroscopic filtration performance and is recommended to be resolved in the filtration model to simulate and evaluate the filtration performance of GPFs.« less

Importance of filter’s microstructure in dynamic filtration modeling of gasoline particulate filters (GPFs): Inhomogeneous porosity and pore size distribution

DOE PAGES

Gong, Jian; Stewart, Mark L.; Zelenyuk, Alla; ...

2018-01-03

The state-of-the-art multiscale modeling of gasoline particulate filter (GPF) including channel scale, wall scale, and pore scale is described. The microstructures of two GPFs were experimentally characterized. The pore size distributions of the GPFs were determined by mercury porosimetry. The porosity was measured by X-ray computed tomography (CT) and found to be inhomogeneous across the substrate wall. The significance of pore size distribution with respect to filtration performance was analyzed. The predictions of filtration efficiency were improved by including the pore size distribution in the filtration model. A dynamic heterogeneous multiscale filtration (HMF) model was utilized to simulate particulate filtrationmore » on a single channel particulate filter with realistic particulate emissions from a spark-ignition direct-injection (SIDI) gasoline engine. The dynamic evolution of filter’s microstructure and macroscopic filtration characteristics including mass- and number-based filtration efficiencies and pressure drop were predicted and discussed. In conclusion, the microstructure of the GPF substrate including inhomogeneous porosity and pore size distribution is found to significantly influence local particulate deposition inside the substrate and macroscopic filtration performance and is recommended to be resolved in the filtration model to simulate and evaluate the filtration performance of GPFs.« less

Importance of filter’s microstructure in dynamic filtration modeling of gasoline particulate filters (GPFs): Inhomogeneous porosity and pore size distribution

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gong, Jian; Stewart, Mark L.; Zelenyuk, Alla

The state-of-the-art multiscale modeling of gasoline particulate filter (GPF) including channel scale, wall scale, and pore scale is described. The microstructures of two GPFs were experimentally characterized. The pore size distributions of the GPFs were determined by mercury porosimetry. The porosity was measured by X-ray computed tomography (CT) and found to be inhomogeneous across the substrate wall. The significance of pore size distribution with respect to filtration performance was analyzed. The predictions of filtration efficiency were improved by including the pore size distribution in the filtration model. A dynamic heterogeneous multiscale filtration (HMF) model was utilized to simulate particulate filtrationmore » on a single channel particulate filter with realistic particulate emissions from a spark-ignition direct-injection (SIDI) gasoline engine. The dynamic evolution of filter’s microstructure and macroscopic filtration characteristics including mass- and number-based filtration efficiencies and pressure drop were predicted and discussed. In conclusion, the microstructure of the GPF substrate including inhomogeneous porosity and pore size distribution is found to significantly influence local particulate deposition inside the substrate and macroscopic filtration performance and is recommended to be resolved in the filtration model to simulate and evaluate the filtration performance of GPFs.« less

Role of medium heterogeneity and viscosity contrast in miscible flow regimes and mixing zone growth: A computational pore-scale approach

NASA Astrophysics Data System (ADS)

Afshari, Saied; Hejazi, S. Hossein; Kantzas, Apostolos

2018-05-01

Miscible displacement of fluids in porous media is often characterized by the scaling of the mixing zone length with displacement time. Depending on the viscosity contrast of fluids, the scaling law varies between the square root relationship, a sign for dispersive transport regime during stable displacement, and the linear relationship, which represents the viscous fingering regime during an unstable displacement. The presence of heterogeneities in a porous medium significantly affects the scaling behavior of the mixing length as it interacts with the viscosity contrast to control the mixing of fluids in the pore space. In this study, the dynamics of the flow and transport during both unit and adverse viscosity ratio miscible displacements are investigated in heterogeneous packings of circular grains using pore-scale numerical simulations. The pore-scale heterogeneity level is characterized by the variations of the grain diameter and velocity field. The growth of mixing length is employed to identify the nature of the miscible transport regime at different viscosity ratios and heterogeneity levels. It is shown that as the viscosity ratio increases to higher adverse values, the scaling law of mixing length gradually shifts from dispersive to fingering nature up to a certain viscosity ratio and remains almost the same afterwards. In heterogeneous media, the mixing length scaling law is observed to be generally governed by the variations of the velocity field rather than the grain size. Furthermore, the normalization of mixing length temporal plots with respect to the governing parameters of viscosity ratio, heterogeneity, medium length, and medium aspect ratio is performed. The results indicate that mixing length scales exponentially with log-viscosity ratio and grain size standard deviation while the impact of aspect ratio is insignificant. For stable flows, mixing length scales with the square root of medium length, whereas it changes linearly with length during unstable flows. This scaling procedure allows us to describe the temporal variation of mixing length using a generalized curve for various combinations of the flow conditions and porous medium properties.

Connecting the molecular scale to the continuum scale for diffusion processes in smectite-rich porous media.

PubMed

Bourg, Ian C; Sposito, Garrison

2010-03-15

In this paper, we address the manner in which the continuum-scale diffusive properties of smectite-rich porous media arise from their molecular- and pore-scale features. Our starting point is a successful model of the continuum-scale apparent diffusion coefficient for water tracers and cations, which decomposes it as a sum of pore-scale terms describing diffusion in macropore and interlayer "compartments." We then apply molecular dynamics (MD) simulations to determine molecular-scale diffusion coefficients D(interlayer) of water tracers and representative cations (Na(+), Cs(+), Sr(2+)) in Na-smectite interlayers. We find that a remarkably simple expression relates D(interlayer) to the pore-scale parameter δ(nanopore) ≤ 1, a constrictivity factor that accounts for the lower mobility in interlayers as compared to macropores: δ(nanopore) = D(interlayer)/D(0), where D(0) is the diffusion coefficient in bulk liquid water. Using this scaling expression, we can accurately predict the apparent diffusion coefficients of tracers H(2)0, Na(+), Sr(2+), and Cs(+) in compacted Na-smectite-rich materials.

Experimental evidence of chaotic mixing at pore scale in 3D porous media

NASA Astrophysics Data System (ADS)

Heyman, J.; Turuban, R.; Jimenez Martinez, J.; Lester, D. R.; Meheust, Y.; Le Borgne, T.

2017-12-01

Mixing of dissolved chemical species in porous media plays a central role in many natural and industrial processes, such as contaminant transport and degradation in soils, oxygen and nitrates delivery in river beds, clogging in geothermal systems, CO2 sequestration. In particular, incomplete mixing at the pore scale may strongly affect the spatio-temporal distribution of reaction rates in soils and rocks, questioning the validity of diffusion-reaction models at the Darcy scale. Recent theoretical [1] and numerical [2] studies of flow in idealized porous media have suggested that fluid mixing may be chaotic at pore scale, hence pointing to a whole new set of models for mixing and reaction in porous media. However, so far this remained to be confirmed experimentally. Here we present experimental evidence of the chaotic nature of transverse mixing at the pore scale in three-dimensional porous media. We designed a novel experimental setup allowing high resolution pore scale imaging of the structure of a tracer plume in porous media columns consisting of 7, 10 and 20 mm glass bead packings. We conjointly used refractive index matching techniques, laser induced fluorescence and a moving laser-sheet to reconstruct the shape of a steady tracer plume as it gets deformed by the porous media flow. In this talk, we focus on the transverse behavior of mixing, that is, on the plane orthogonal to the main flow direction, in the limit of high Péclet numbers (diffusion is negligible). Moving away from the injection point, the plume cross-section turns quickly into complex, interlaced, lamellar structures. These structures elongated at an exponential rate, characteristic of a chaotic system, that can be characterized by an average Lyapunov exponent. We finally discuss the origin of this chaotic behavior and its most significant consequences for upscaling mixing and reactive transport in porous media. Reference:[1] D. R. Lester, G. Metcafle, M. G. Trefry, Physical Review Letters, 111, 174101 (2013) [2] R. Turuban, D. R. Lester, T. Le Borgne, and Y. Méheust (2017), under review.

Experimental Quantification of Pore-Scale Flow Phenomena in 2D Heterogeneous Porous Micromodels: Multiphase Flow Towards Coupled Solid-Liquid Interactions

NASA Astrophysics Data System (ADS)

Li, Y.; Kazemifar, F.; Blois, G.; Christensen, K. T.

2017-12-01

Geological sequestration of CO2 within saline aquifers is a viable technology for reducing CO2 emissions. Central to this goal is accurately predicting both the fidelity of candidate sites pre-injection of CO2 and its post-injection migration. Moreover, local fluid pressure buildup may cause activation of small pre-existing unidentified faults, leading to micro-seismic events, which could prove disastrous for societal acceptance of CCS, and possibly compromise seal integrity. Recent evidence shows that large-scale events are coupled with pore-scale phenomena, which necessitates the representation of pore-scale stress, strain, and multiphase flow processes in large-scale modeling. To this end, the pore-scale flow of water and liquid/supercritical CO2 is investigated under reservoir-relevant conditions, over a range of wettability conditions in 2D heterogeneous micromodels that reflect the complexity of a real sandstone. High-speed fluorescent microscopy, complemented by a fast differential pressure transmitter, allows for simultaneous measurement of the flow field within and the instantaneous pressure drop across the micromodels. A flexible micromodel is also designed and fabricated, to be used in conjunction with the micro-PIV technique, enabling the quantification of coupled solid-liquid interactions.

The processing of aluminum gasarites via thermal decomposition of interstitial hydrides

NASA Astrophysics Data System (ADS)

Licavoli, Joseph J.

Gasarite structures are a unique type of metallic foam containing tubular pores. The original methods for their production limited them to laboratory study despite appealing foam properties. Thermal decomposition processing of gasarites holds the potential to increase the application of gasarite foams in engineering design by removing several barriers to their industrial scale production. The following study characterized thermal decomposition gasarite processing both experimentally and theoretically. It was found that significant variation was inherent to this process therefore several modifications were necessary to produce gasarites using this method. Conventional means to increase porosity and enhance pore morphology were studied. Pore morphology was determined to be more easily replicated if pores were stabilized by alumina additions and powders were dispersed evenly. In order to better characterize processing, high temperature and high ramp rate thermal decomposition data were gathered. It was found that the high ramp rate thermal decomposition behavior of several hydrides was more rapid than hydride kinetics at low ramp rates. This data was then used to estimate the contribution of several pore formation mechanisms to the development of pore structure. It was found that gas-metal eutectic growth can only be a viable pore formation mode if non-equilibrium conditions persist. Bubble capture cannot be a dominant pore growth mode due to high bubble terminal velocities. Direct gas evolution appears to be the most likely pore formation mode due to high gas evolution rate from the decomposing particulate and microstructural pore growth trends. The overall process was evaluated for its economic viability. It was found that thermal decomposition has potential for industrialization, but further refinements are necessary in order for the process to be viable.

Wettability effect on capillary trapping of supercritical CO2 at pore-scale: micromodel experiment and numerical modeling

NASA Astrophysics Data System (ADS)

Hu, R.; Wan, J.

2015-12-01

Wettability of reservoir minerals along pore surfaces plays a controlling role in capillary trapping of supercritical (sc) CO2 in geologic carbon sequestration. The mechanisms controlling scCO2 residual trapping are still not fully understood. We studied the effect of pore surface wettability on CO2 residual saturation at the pore-scale using engineered high pressure and high temperature micromodel (transparent pore networks) experiments and numerical modeling. Through chemical treatment of the micromodel pore surfaces, water-wet, intermediate-wet, and CO2-wet micromodels can be obtained. Both drainage and imbibition experiments were conducted at 8.5 MPa and 45 °C with controlled flow rate. Dynamic images of fluid-fluid displacement processes were recorded using a microscope with a CCD camera. Residual saturations were determined by analysis of late stage imbibition images of flow path structures. We performed direct numerical simulations of the full Navier-Stokes equations using a volume-of-fluid based finite-volume framework for the primary drainage and the followed imbibition for the micromodel experiments with different contact angles. The numerical simulations agreed well with our experimental observations. We found that more scCO2 can be trapped within the CO2-wet micromodel whereas lower residual scCO2 saturation occurred within the water-wet micromodels in both our experiments and the numerical simulations. These results provide direct and consistent evidence of the effect of wettability, and have important implications for scCO2 trapping in geologic carbon sequestration.

A molecular dynamics study of the pores formed by Escherichia coli OmpF porin in a fully hydrated palmitoyloleoylphosphatidylcholine bilayer.

PubMed

Tieleman, D P; Berendsen, H J

1998-06-01

In this paper we study the properties of pores formed by OmpF porin from Escherichia coli, based on a molecular dynamics simulation of the OmpF trimer, 318 palmitoyl-oleoyl-phosphatidylethanolamine lipids, 27 Na+ ions, and 12,992 water molecules. After equilibration and a nanosecond production run, the OmpF trimer exhibits a C-alpha root mean square deviation from the crystal structure of 0.23 nm and a stable secondary structure. No evidence is found for large-scale motions of the L3 loop. We investigate the pore dimensions, conductance, and the properties of water inside the pore. This water forms a complicated pattern, even when averaged over 1 ns of simulation time. Around the pore constriction zone the water dipoles are highly structured in the plane of the membrane, oriented by the strong transversal electric field. In addition, there is a net orientation along the pore axis pointing from the extracellular to the intracellular side of the bilayer. The diffusion coefficients of water inside the pore are greatly reduced compared to bulk. We compare our results to results from model pores (Breed et al., 1996. Biophys. J. 70:1 643-1 661; Sansom et al. 1997. Biophys. J. 73:2404-241 5) and discuss implications for further theoretical work.

Wettability control of micropore-array films by altering the surface nanostructures.

PubMed

Chang, Chi-Jung; Hung, Shao-Tsu

2010-07-01

By controlling the surface nanostructure, the wettability of films with similar pore-array microstructure can be tuned from hydrophilic to nearly superhydrophobic without variation of the chemical composition. PA1 pore-array film consisting of the horizontal ZnO nanosheets was nearly superhydrophobic. PA2 pore-array film consisting of growth-hindered vertically-aligned ZnO nanorods was hydrophilic. The influences of the nanostructure shape, orientation and the micropore size on the contact angle of the PA1 films were studied. This study provides a new approach to control the wettability of films with similar pore-array structure at the micro-scale by changing their surface nanostructure. PA1 films exhibited irradiation induced reversible wettability transition. The feasibility of creating a wetted radial pattern by selective UV irradiation of PA1 film through a mask with radial pattern and water vapor condensation was also evaluated.

Monitoring CO2 invasion processes at the pore scale using geological labs on chip.

PubMed

Morais, S; Liu, N; Diouf, A; Bernard, D; Lecoutre, C; Garrabos, Y; Marre, S

2016-09-21

In order to investigate at the pore scale the mechanisms involved during CO2 injection in a water saturated pore network, a series of displacement experiments is reported using high pressure micromodels (geological labs on chip - GLoCs) working under real geological conditions (25 < T (°C) < 75 and 4.5 < p (MPa) < 8). The experiments were focused on the influence of three experimental parameters: (i) the p, T conditions, (ii) the injection flow rates and (iii) the pore network characteristics. By using on-chip optical characterization and imaging approaches, the CO2 saturation curves as a function of either time or the number of pore volume injected were determined. Three main mechanisms were observed during CO2 injection, namely, invasion, percolation and drying, which are discussed in this paper. Interestingly, besides conventional mechanisms, two counterintuitive situations were observed during the invasion and drying processes.

Quantification of soil structure based on Minkowski functions

NASA Astrophysics Data System (ADS)

Vogel, H.-J.; Weller, U.; Schlüter, S.

2010-10-01

The structure of soils and other geologic media is a complex three-dimensional object. Most of the physical material properties including mechanical and hydraulic characteristics are immediately linked to the structure given by the pore space and its spatial distribution. It is an old dream and still a formidable challenge to relate structural features of porous media to their functional properties. Using tomographic techniques, soil structure can be directly observed at a range of spatial scales. In this paper we present a scale-invariant concept to quantify complex structures based on a limited set of meaningful morphological functions. They are based on d+1 Minkowski functionals as defined for d-dimensional bodies. These basic quantities are determined as a function of pore size or aggregate size obtained by filter procedures using mathematical morphology. The resulting Minkowski functions provide valuable information on the size of pores and aggregates, the pore surface area and the pore topology having the potential to be linked to physical properties. The theoretical background and the related algorithms are presented and the approach is demonstrated for the pore structure of an arable soil and the pore structure of a sand both obtained by X-ray micro-tomography. We also analyze the fundamental problem of limited resolution which is critical for any attempt to quantify structural features at any scale using samples of different size recorded at different resolutions. The results demonstrate that objects smaller than 5 voxels are critical for quantitative analysis.

Accounting for microbial habitats in modeling soil organic matter dynamics

NASA Astrophysics Data System (ADS)

Chenu, Claire; Garnier, Patricia; Nunan, Naoise; Pot, Valérie; Raynaud, Xavier; Vieublé, Laure; Otten, Wilfred; Falconer, Ruth; Monga, Olivier

2017-04-01

The extreme heterogeneity of soils constituents, architecture and inhabitants at the microscopic scale is increasingly recognized. Microbial communities exist and are active in a complex 3-D physical framework of mineral and organic particles defining pores of various sizes, more or less inter-connected. This results in a frequent spatial disconnection between soil carbon, energy sources and the decomposer organisms and a variety of microhabitats that are more or less suitable for microbial growth and activity. However, current biogeochemical models account for C dynamics at the macroscale (cm, m) and consider time- and spatially averaged relationships between microbial activity and soil characteristics. Different modelling approaches have intended to account for this microscale heterogeneity, based either on considering aggregates as surrogates for microbial habitats, or pores. Innovative modelling approaches are based on an explicit representation of soil structure at the fine scale, i.e. at µm to mm scales: pore architecture and their saturation with water, localization of organic resources and of microorganisms. Three recent models are presented here, that describe the heterotrophic activity of either bacteria or fungi and are based upon different strategies to represent the complex soil pore system (Mosaic, LBios and µFun). These models allow to hierarchize factors of microbial activity in soil's heterogeneous architecture. Present limits of these approaches and challenges are presented, regarding the extensive information required on soils at the microscale and to up-scale microbial functioning from the pore to the core scale.

Plasma flows and magnetic field interplay during the formation of a pore

NASA Astrophysics Data System (ADS)

Ermolli, I.; Cristaldi, A.; Giorgi, F.; Giannattasio, F.; Stangalini, M.; Romano, P.; Tritschler, A.; Zuccarello, F.

2017-04-01

Aims: Recent simulations of solar magneto-convection have offered new levels of understanding of the interplay between plasma motions and magnetic fields in evolving active regions. We aim at verifying some aspects of the formation of magnetic regions derived from recent numerical studies in observational data. Methods: We studied the formation of a pore in the active region (AR) NOAA 11462. We analysed data obtained with the Interferometric Bidimensional Spectrometer (IBIS) at the Dunn Solar Telescope on April 17, 2012, consisting of full Stokes measurements of the Fe I 617.3 nm lines. Furthermore, we analysed SDO/HMI observations in the continuum and vector magnetograms derived from the Fe I 617.3 nm line data taken from April 15 to 19, 2012. We estimated the magnetic field strength and vector components and the line-of-sight (LOS) and horizontal motions in the photospheric region hosting the pore formation. We discuss our results in light of other observational studies and recent advances of numerical simulations. Results: The pore formation occurs in less than 1 h in the leading region of the AR. We observe that the evolution of the flux patch in the leading part of the AR is faster (<12 h) than the evolution (20-30 h) of the more diffuse and smaller scale flux patches in the trailing region. During the pore formation, the ratio between magnetic and dark area decreases from 5 to 2. We observe strong downflows at the forming pore boundary and diverging proper motions of plasma in the vicinity of the evolving feature that are directed towards the forming pore. The average values and trends of the various quantities estimated in the AR are in agreement with results of former observational studies of steady pores and with their modelled counterparts, as seen in recent numerical simulations of a rising-tube process. The agreement with the outcomes of the numerical studies holds for both the signatures of the flux emergence process (e.g. appearance of small-scale mixed polarity patterns and elongated granules) and the evolution of the region. The processes driving the formation of the pore are identified with the emergence of a magnetic flux concentration and the subsequent reorganization of the emerged flux, by the combined effect of velocity and magnetic field, in and around the evolving structure. Movies associated to Figs. 1 and 4 are available at http://www.aanda.org

A USANS/SANS study of the accessibility of pores in the Barnett Shale to methane and water

USGS Publications Warehouse

Ruppert, Leslie F.; Sakurovs, Richard; Blach, Tomasz P.; He, Lilin; Melnichenko, Yuri B.; Mildner, David F.; Alcantar-Lopez, Leo

2013-01-01

Shale is an increasingly important source of natural gas in the United States. The gas is held in fine pores that need to be accessed by horizontal drilling and hydrofracturing techniques. Understanding the nature of the pores may provide clues to making gas extraction more efficient. We have investigated two Mississippian Barnett Shale samples, combining small-angle neutron scattering (SANS) and ultrasmall-angle neutron scattering (USANS) to determine the pore size distribution of the shale over the size range 10 nm to 10 μm. By adding deuterated methane (CD4) and, separately, deuterated water (D2O) to the shale, we have identified the fraction of pores that are accessible to these compounds over this size range. The total pore size distribution is essentially identical for the two samples. At pore sizes >250 nm, >85% of the pores in both samples are accessible to both CD4 and D2O. However, differences in accessibility to CD4 are observed in the smaller pore sizes (~25 nm). In one sample, CD4 penetrated the smallest pores as effectively as it did the larger ones. In the other sample, less than 70% of the smallest pores (4, but they were still largely penetrable by water, suggesting that small-scale heterogeneities in methane accessibility occur in the shale samples even though the total porosity does not differ. An additional study investigating the dependence of scattered intensity with pressure of CD4 allows for an accurate estimation of the pressure at which the scattered intensity is at a minimum. This study provides information about the composition of the material immediately surrounding the pores. Most of the accessible (open) pores in the 25 nm size range can be associated with either mineral matter or high reflectance organic material. However, a complementary scanning electron microscopy investigation shows that most of the pores in these shale samples are contained in the organic components. The neutron scattering results indicate that the pores are not equally proportioned in the different constituents within the shale. There is some indication from the SANS results that the composition of the pore-containing material varies with pore size; the pore size distribution associated with mineral matter is different from that associated with organic phases.

A multi-scale Lattice Boltzmann model for simulating solute transport in 3D X-ray micro-tomography images of aggregated porous materials

NASA Astrophysics Data System (ADS)

Zhang, Xiaoxian; Crawford, John W.; Flavel, Richard J.; Young, Iain M.

2016-10-01

The Lattice Boltzmann (LB) model and X-ray computed tomography (CT) have been increasingly used in combination over the past decade to simulate water flow and chemical transport at pore scale in porous materials. Because of its limitation in resolution and the hierarchical structure of most natural soils, the X-ray CT tomography can only identify pores that are greater than its resolution and treats other pores as solid. As a result, the so-called solid phase in X-ray images may in reality be a grey phase, containing substantial connected pores capable of conducing fluids and solute. Although modified LB models have been developed to simulate fluid flow in such media, models for solute transport are relatively limited. In this paper, we propose a LB model for simulating solute transport in binary soil images containing permeable solid phase. The model is based on the single-relaxation time approach and uses a modified partial bounce-back method to describe the resistance caused by the permeable solid phase to chemical transport. We derive the relationship between the diffusion coefficient and the parameter introduced in the partial bounce-back method, and test the model against analytical solution for movement of a pulse of tracer. We also validate it against classical finite volume method for solute diffusion in a simple 2D image, and then apply the model to a soil image acquired using X-ray tomography at resolution of 30 μm in attempts to analyse how the ability of the solid phase to diffuse solute at micron-scale affects the behaviour of the solute at macro-scale after a volumetric average. Based on the simulated results, we discuss briefly the danger in interpreting experimental results using the continuum model without fully understanding the pore-scale processes, as well as the potential of using pore-scale modelling and tomography to help improve the continuum models.

Chemical synthesis, characterisation, and biocompatibility of nanometre scale porous anodic aluminium oxide membranes for use as a cell culture substrate for the vero cell line: a preliminary study.

PubMed

Poinern, Gérrard Eddy Jai; Le, Xuan Thi; O'Dea, Mark; Becker, Thomas; Fawcett, Derek

2014-01-01

In this preliminary study we investigate for the first time the biomedical potential of using porous anodic aluminium oxide (AAO) membranes as a cell substrate for culturing the Cercopithecus aethiops (African green monkey) Kidney (Vero) epithelial cell line. One advantage of using the inorganic AAO membrane is the presence of nanometre scale pore channels that allow the exchange of molecules and nutrients across the membrane. The size of the pore channels can be preselected by adjusting the controlling parameters of a temperature controlled two-step anodization process. The cellular interaction and response of the Vero cell line with an in-house synthesised AAO membrane, a commercially available membrane, and a glass control were assessed by investigating cell adhesion, morphology, and proliferation over a 72 h period. The number of viable cells proliferating over the respective membrane surfaces revealed that the locally produced in-house AAO membrane had cells numbers similar to the glass control. The study revealed evidence of focal adhesion sites over the surface of the nanoporous membranes and the penetration of cellular extensions into the pore structure as well. The outcome of the study has revealed that nanometre scale porous AAO membranes have the potential to become practical cell culture scaffold substrates with the capability to enhance adhesion and proliferation of Vero cells.

Chemical Synthesis, Characterisation, and Biocompatibility of Nanometre Scale Porous Anodic Aluminium Oxide Membranes for Use as a Cell Culture Substrate for the Vero Cell Line: A Preliminary Study

PubMed Central

Poinern, Gérrard Eddy Jai; Le, Xuan Thi; Becker, Thomas; Fawcett, Derek

2014-01-01

In this preliminary study we investigate for the first time the biomedical potential of using porous anodic aluminium oxide (AAO) membranes as a cell substrate for culturing the Cercopithecus aethiops (African green monkey) Kidney (Vero) epithelial cell line. One advantage of using the inorganic AAO membrane is the presence of nanometre scale pore channels that allow the exchange of molecules and nutrients across the membrane. The size of the pore channels can be preselected by adjusting the controlling parameters of a temperature controlled two-step anodization process. The cellular interaction and response of the Vero cell line with an in-house synthesised AAO membrane, a commercially available membrane, and a glass control were assessed by investigating cell adhesion, morphology, and proliferation over a 72 h period. The number of viable cells proliferating over the respective membrane surfaces revealed that the locally produced in-house AAO membrane had cells numbers similar to the glass control. The study revealed evidence of focal adhesion sites over the surface of the nanoporous membranes and the penetration of cellular extensions into the pore structure as well. The outcome of the study has revealed that nanometre scale porous AAO membranes have the potential to become practical cell culture scaffold substrates with the capability to enhance adhesion and proliferation of Vero cells. PMID:24579077

Ultra-Long Time Dynamics of Contaminant Plume Mixing Induced by Transient Forcing Factors in Geologic Formations

NASA Astrophysics Data System (ADS)

Rajabi, F.; Battiato, I.

2016-12-01

Long term predictions of the impact of anthropogenic stressors on the environment is essential to reduce the risks associated with processes such as CO2 sequestration and nuclear waste storage in the subsurface. On the other hand, transient forcing factors (e.g. time-varying injection or pumping rate) with evolving heterogeneity of time scales spanning from days to years can influence transport phenomena at the pore scale. A comprehensive spatio-temporal prediction of reactive transport in porous media under time-dependent forcing factors for thousands of years requires the formulation of continuum scale models for time-averages. Yet, as every macroscopic model, time-averaged models can loose predictivity and accuracy when certain conditions are violated. This is true whenever lack of temporal and spatial scale separation occurs and it makes the continuum scale equation a poor assumption for the processes at the pore scale. In this work, we consider mass transport of a dissolved species undergoing a heterogeneous reaction and subject to time-varying boundary conditions in a periodic porous medium. By means of homogenization method and asymptotic expansion technique, we derive a macro-time continuum-scale equation as well as expressions for its effective properties. Our analysis demonstrates that the dynamics at the macro-scale is strongly influenced by the interplay between signal frequency at the boundary and transport processes at the pore level. In addition, we provide the conditions under which the space-time averaged equations accurately describe pore-scale processes. To validate our theoretical predictions, we consider a thin fracture with reacting walls and transient boundary conditions at the inlet. Our analysis shows a good agreement between numerical simulations and theoretical predictions. Furthermore, our numerical experiments show that mixing patterns of the contaminant plumes at the pore level strongly depend on the signal frequency.

Adaptive Multiscale Modeling of Geochemical Impacts on Fracture Evolution

NASA Astrophysics Data System (ADS)

Molins, S.; Trebotich, D.; Steefel, C. I.; Deng, H.

2016-12-01

Understanding fracture evolution is essential for many subsurface energy applications, including subsurface storage, shale gas production, fracking, CO2 sequestration, and geothermal energy extraction. Geochemical processes in particular play a significant role in the evolution of fractures through dissolution-driven widening, fines migration, and/or fracture sealing due to precipitation. One obstacle to understanding and exploiting geochemical fracture evolution is that it is a multiscale process. However, current geochemical modeling of fractures cannot capture this multi-scale nature of geochemical and mechanical impacts on fracture evolution, and is limited to either a continuum or pore-scale representation. Conventional continuum-scale models treat fractures as preferential flow paths, with their permeability evolving as a function (often, a cubic law) of the fracture aperture. This approach has the limitation that it oversimplifies flow within the fracture in its omission of pore scale effects while also assuming well-mixed conditions. More recently, pore-scale models along with advanced characterization techniques have allowed for accurate simulations of flow and reactive transport within the pore space (Molins et al., 2014, 2015). However, these models, even with high performance computing, are currently limited in their ability to treat tractable domain sizes (Steefel et al., 2013). Thus, there is a critical need to develop an adaptive modeling capability that can account for separate properties and processes, emergent and otherwise, in the fracture and the rock matrix at different spatial scales. Here we present an adaptive modeling capability that treats geochemical impacts on fracture evolution within a single multiscale framework. Model development makes use of the high performance simulation capability, Chombo-Crunch, leveraged by high resolution characterization and experiments. The modeling framework is based on the adaptive capability in Chombo which not only enables mesh refinement, but also refinement of the model-pore scale or continuum Darcy scale-in a dynamic way such that the appropriate model is used only when and where it is needed. Explicit flux matching provides coupling betwen the scales.

Percolation Network Study on the Gas Apparent Permeability of Rock

NASA Astrophysics Data System (ADS)

Wang, Y.; Tang, Y. B.; Li, M.

2017-12-01

We modeled the gas single phase transport behaviors of monomodal porous media using percolation networks. Different from the liquid absolute permeability, which is only related to topology and morphology of pore space, the gas permeability depends on pore pressure as well. A published gas flow conductance model, included usual viscous flow, slip flow and Knudsen diffusion in cylinder pipe, was used to simulated gas flow in 3D, simple cubic, body-center cubic and face-center cubic networks with different hydraulic radius, different coordination number, and different pipe radius distributions under different average pore pressure. The simulation results showed that the gas apparent permeability kapp obey the `universal' scaling law (independence of network lattices), kapp (z-zc)β, where exponent β is related to pore radius distribution, z is coordination number and zc=1.5. Following up on Bernabé et al.'s (2010) study of the effects of pore connectivity and pore size heterogeneity on liquid absolute permeability, gas apparent permeability kapp model and a new joint gas-liquid permeability (i.e., kapp/k∞) model, which could explain the Klinkenberg phenomenon, were proposed. We satisfactorily tested the models by comparison with published experimental data on glass beads and other datasets.

Porosity characterization for heterogeneous shales using integrated multiscale microscopy

NASA Astrophysics Data System (ADS)

Rassouli, F.; Andrew, M.; Zoback, M. D.

2016-12-01

Pore size distribution analysis plays a critical role in gas storage capacity and fluid transport characterization of shales. Study of the diverse distribution of pore size and structure in such low permeably rocks is withheld by the lack of tools to visualize the microstructural properties of shale rocks. In this paper we try to use multiple techniques to investigate the full pore size range in different sample scales. Modern imaging techniques are combined with routine analytical investigations (x-ray diffraction, thin section analysis and mercury porosimetry) to describe pore size distribution of shale samples from Haynesville formation in East Texas to generate a more holistic understanding of the porosity structure in shales, ranging from standard core plug down to nm scales. Standard 1" diameter core plug samples were first imaged using a Versa 3D x-ray microscope at lower resolutions. Then we pick several regions of interest (ROIs) with various micro-features (such as micro-cracks and high organic matters) in the rock samples to run higher resolution CT scans using a non-destructive interior tomography scans. After this step, we cut the samples and drill 5 mm diameter cores out of the selected ROIs. Then we rescan the samples to measure porosity distribution of the 5 mm cores. We repeat this step for samples with diameter of 1 mm being cut out of the 5 mm cores using a laser cutting machine. After comparing the pore structure and distribution of the samples measured form micro-CT analysis, we move to nano-scale imaging to capture the ultra-fine pores within the shale samples. At this stage, the diameter of the 1 mm samples will be milled down to 70 microns using the laser beam. We scan these samples in a nano-CT Ultra x-ray microscope and calculate the porosity of the samples by image segmentation methods. Finally, we use images collected from focused ion beam scanning electron microscopy (FIB-SEM) to be able to compare the results of porosity measurements from all different imaging techniques. These multi-scale characterization techniques are then compared with traditional analytical techniques such as Mercury Porosimetry.

Variations in Multiscale (nano to mm) Porosity in the Eagle Ford Shale as a Function of Maturity through the Oil Window

NASA Astrophysics Data System (ADS)

Anovitz, L. M.; Cole, D. R.; Swift, A.; Sheets, J.; Elston, H. W.; Gutierrez, M. A.; Cook, A.; Chipera, S.; Littrell, K. C.; Mildner, D. F.; Wasbrough, M.

2013-12-01

Porosity and permeability are key variables that link the thermal-hydrologic, geomechanical and geochemical behavior in rock systems and are thus important input parameters for transport models. Recent neutron scattering studies have indicated that the scales of pore sizes in rocks extend over many orders of magnitude from nanometer pores with huge amounts of total surface area to large open fracture systems (multiscale porosity, cf. Anovitz et al., 2009, 2011, 2013a,b). However, despite a considerable amount of effort combining conventional rock petrophysics with more sophisticated neutron scattering and electron microscopy studies, the quantitative nature of this porosity in tight gas shales, especially at smaller scales and over larger rock volumes, remains largely unknown (Clarkson, 2011). We lack a quantitative understanding of the multiscale porosity regime (i.e., pore size, shape, and volume, pore size distribution, pore connectivity, pore wall roughness) in rocks. Nor is it understood how porosity is affected by regional variation, thermal changes across the oil window, and, most critically, hydraulic fracturing operations. In order to begin to provide a quantitative understanding of porosity at nanometer to core scales in these shale formations and how it relates to gas storage and recovery we have used a combination of small and ultrasmall angle neutron scattering measurments made on the GP-SANS instrument at ORNL/HFIR, and the NG3-SANS and BT5-USANS instruments and NIST/NCNR, with SEM/BSE and X-ray Computed Tomographic imaging to analyze the pore structure of both clay and carbonate-rich samples of the Eagle Ford Shale. The Eagle Ford Shale is a late Cretaceous unit underlying much of southeast Texas and probably adjacent sections of Mexico. It outcrops in an arc from north of Austin, through San Antonio and then west towards Kinney County. It is hydrocarbon rich, and buried portions straddle the oil window. The Eagle Ford is currently one of the most actively drilled oil and gas targets in the US. The first successful horizontal well was drilled in 2008, and 2522 permits were recorded (Texas railroad commission) by Sept 1, 2011. While the oil and gas reserves in the Eagle Ford have been known since the 1970's, prior to the invention of horizontal drilling/hydraulic fracturing it was not considered economic. Several important trends in the rock pore structure have been identified using our approach. Pore distributions are clearly fractal but, as was observed for the St. Peter sandstone (Anovitz et al., 2013a), are composed of several size distributions. Initial porosity is strongly anisotropic, as expected for shales. However, this decreases for shales, and disappears for carbonates with maturity. In both cases significant reduction occurs in total porosity, with most of the change coming at the finest scales (< ~ 10 nm), and an observable decrease at intermediate scales (near 100 nm) Research sponsored by the Division of Chemical Sciences, Geosciences, and Biosciences, Office of Basic Energy Sciences, U.S. Department of Energy, and as part of the Center for Nanoscale Control of Geologic CO2, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science under U.S. Dept. of Energy (DOE) contract DE-AC02-05CH11231.

Convex hull approach for determining rock representative elementary volume for multiple petrophysical parameters using pore-scale imaging and Lattice-Boltzmann modelling

NASA Astrophysics Data System (ADS)

Shah, S. M.; Crawshaw, J. P.; Gray, F.; Yang, J.; Boek, E. S.

2017-06-01

In the last decade, the study of fluid flow in porous media has developed considerably due to the combination of X-ray Micro Computed Tomography (micro-CT) and advances in computational methods for solving complex fluid flow equations directly or indirectly on reconstructed three-dimensional pore space images. In this study, we calculate porosity and single phase permeability using micro-CT imaging and Lattice Boltzmann (LB) simulations for 8 different porous media: beadpacks (with bead sizes 50 μm and 350 μm), sandpacks (LV60 and HST95), sandstones (Berea, Clashach and Doddington) and a carbonate (Ketton). Combining the observed porosity and calculated single phase permeability, we shed new light on the existence and size of the Representative Element of Volume (REV) capturing the different scales of heterogeneity from the pore-scale imaging. Our study applies the concept of the 'Convex Hull' to calculate the REV by considering the two main macroscopic petrophysical parameters, porosity and single phase permeability, simultaneously. The shape of the hull can be used to identify strong correlation between the parameters or greatly differing convergence rates. To further enhance computational efficiency we note that the area of the convex hull (for well-chosen parameters such as the log of the permeability and the porosity) decays exponentially with sub-sample size so that only a few small simulations are needed to determine the system size needed to calculate the parameters to high accuracy (small convex hull area). Finally we propose using a characteristic length such as the pore size to choose an efficient absolute voxel size for the numerical rock.

Coupled Electro-Hydrodynamic Effects of Electro-Osmosis from Pore Scale to Darcy Scale

NASA Astrophysics Data System (ADS)

Schotting, R.; Joekar-Niasar, V.; Leijnse, A.

2011-12-01

Electro-osmosis is "movement of a fluid under the effect of an electric field in a porous medium". This phenomenon has many applications in civil engineering (slope stabilization, dewatering), environmental engineering (soil remediation, sludge dewatering), chemical engineering (micro- or nano- mixers), medical engineering (drug delivery), etc. The key factor in electro-osmosis is the competition between the electrochemical and hydrodynamic forces as well as the coupling between the solid surface and the electrolyte properties. The objective of this research is to understand the influence of pore-scale heterogeneities of surface properties on the Darcy-scale behavior. We develop novel analytical solutions for the flow and transport of electrolyte including electro-hydrodynamic forces in a single micro-channel. We propose the complete analytical solution for monovalent electrolyte at full range overlapping double layers, and nonlinear electric field, including the Donan effect in transport of ions. These pore-scale formulations are numerically upscaled to obtain the Darcy-scale behavior. Our results show the contribution of electro-osmotic, chemical-osmotic and hydrodynamic components of the flow equation on pressure field evolution and multi-directional flow field at Darcy scale.

Nonlinear transport of soft droplets in pore networks

NASA Astrophysics Data System (ADS)

Vernerey, Franck; Benet Cerda, Eduard; Koo, Kanghyeon

A large number of biological and technological processes depend on the transport of soft colloidal particles through porous media; this includes the transport and separation of cells, viruses or drugs through tissues, membranes and microfluidic devices. In these systems, the interactions between soft particles, background fluid and the surrounding pore space yield complex, nonlinear behaviors such as non-Darcy flows, localization and jamming. We devise a computational strategy to investigate the transport of non-wetting and deformable water droplets in a microfluidic device made of a random distribution of cylindrical obstacles. We first derive scaling laws for the entry of the droplet in a single pore and discuss the role of surface tension, contact angle and size in this process. This information is then used to study the transport of multiple droplets in an obstacle network. We find that when the droplet size is close to the pore size, fluid flow and droplet trafficking strongly interact, leading to local redistributions in pressure fields, intermittent clogging and jamming. Importantly, it is found that the overall droplet and fluid transport display three different scaling regimes depending on the forcing pressure, and that these regimes can be related to droplet properties.

Storage and recovery of methane-ethane mixtures in single shale pores

NASA Astrophysics Data System (ADS)

Wu, Haiyi; Qiao, Rui

2017-11-01

Natural gas production from shale formations has received extensive attention recently. While great progress has been made in understanding the adsorption and transport of single-component gas inside shales' nanopores, the adsorption and transport of multicomponent shale gas under reservoir conditions (CH4 and C2H6 mixture) has only begun to be studied. In this work, we use molecular simulations to compute the storage of CH4 and C2H6 mixtures in single nanopores and their subsequent recovery. We show that surface adsorption contributes greatly to the storage of CH4 and C2H6 inside the pores and C2H6 is enriched over CH4. The enrichment of C2H6 is enhanced as the pore is narrowed, but is weakened as the pressure increases. We show that the recovery of gas mixtures from the nanopores approximately follows the diffusive scaling law. The ratio of the production rates of C2H6 and CH4 is close to their initial mole ratio inside the pore despite that the mobility of pure C2H6 is much smaller than that of pure CH4 inside the pores. By using scale analysis, we show that the strong coupling between the transport of CH4 and C2H6 is responsible for the effective recovery of C2H6 from the nanopores.

Superdiffusive gas recovery from nanopores

NASA Astrophysics Data System (ADS)

Wu, Haiyi; He, Yadong; Qiao, Rui

2016-11-01

Understanding the recovery of gas from reservoirs featuring pervasive nanopores is essential for effective shale gas extraction. Classical theories cannot accurately predict such gas recovery and many experimental observations are not well understood. Here we report molecular simulations of the recovery of gas from single nanopores, explicitly taking into account molecular gas-wall interactions. We show that, in very narrow pores, the strong gas-wall interactions are essential in determining the gas recovery behavior both quantitatively and qualitatively. These interactions cause the total diffusion coefficients of the gas molecules in nanopores to be smaller than those predicted by kinetic theories, hence slowing down the rate of gas recovery. These interactions also lead to significant adsorption of gas molecules on the pore walls. Because of the desorption of these gas molecules during gas recovery, the gas recovery from the nanopore does not exhibit the usual diffusive scaling law (i.e., the accumulative recovery scales as R ˜t1 /2 ) but follows a superdiffusive scaling law R ˜tn (n >0.5 ), which is similar to that observed in some field experiments. For the system studied here, the superdiffusive gas recovery scaling law can be captured well by continuum models in which the gas adsorption and desorption from pore walls are taken into account using the Langmuir model.

Porosity and permeability determination of organic-rich Posidonia shales based on 3-D analyses by FIB-SEM microscopy

NASA Astrophysics Data System (ADS)

Grathoff, Georg H.; Peltz, Markus; Enzmann, Frieder; Kaufhold, Stephan

2016-07-01

The goal of this study is to better understand the porosity and permeability in shales to improve modelling fluid and gas flow related to shale diagenesis. Two samples (WIC and HAD) were investigated, both mid-Jurassic organic-rich Posidonia shales from Hils area, central Germany of different maturity (WIC R0 0.53 % and HAD R0 1.45 %). The method for image collection was focused ion beam (FIB) microscopy coupled with scanning electron microscopy (SEM). For image and data analysis Avizo and GeoDict was used. Porosity was calculated from segmented 3-D FIB based images and permeability was simulated by a Navier Stokes-Brinkman solver in the segmented images. Results show that the quantity and distribution of pore clusters and pores (≥ 40 nm) are similar. The largest pores are located within carbonates and clay minerals, whereas the smallest pores are within the matured organic matter. Orientation of the pores calculated as pore paths showed minor directional differences between the samples. Both samples have no continuous connectivity of pore clusters along the axes in the x, y, and z direction on the scale of 10 to 20 of micrometer, but do show connectivity on the micrometer scale. The volume of organic matter in the studied volume is representative of the total organic carbon (TOC) in the samples. Organic matter does show axis connectivity in the x, y, and z directions. With increasing maturity the porosity in organic matter increases from close to 0 to more than 5 %. These pores are small and in the large organic particles have little connection to the mineral matrix. Continuous pore size distributions are compared with mercury intrusion porosimetry (MIP) data. Differences between both methods are caused by resolution limits of the FIB-SEM and by the development of small pores during the maturation of the organic matter. Calculations show no permeability when only considering visible pores due to the lack of axis connectivity. Adding the organic matter with a background permeability of 1 × 10-21 m2 to the calculations, the total permeability increased by up to 1 order of magnitude for the low mature and decreases slightly for the overmature sample from the gas window. Anisotropy of permeability was observed. Permeability coefficients increase by 1 order of magnitude if simulations are performed parallel to the bedding. Our results compare well with experimental data from the literature suggesting that upscaling may be possible in the future as soon as maturity dependent organic matter permeability coefficients can be determined.

Fabrication of nanoporous membranes for tuning microbial interactions and biochemical reactions

DOE PAGES

Shankles, Peter G.; Timm, Andrea C.; Doktycz, Mitchel J.; ...

2015-10-21

Here we describe how new strategies for combining conventional photo- and soft- lithographic techniques with high-resolution patterning and etching strategies are needed in order to produce multi-scale fluidic platforms that address the full range of functional scales seen in complex biological and chemical systems. The smallest resolution required for an application often dictates the fabrication method used. Micromachining and micro-powder blasting yield higher throughput, but lack the resolution needed to fully address biological and chemical systems at the cellular and molecular scales. In contrast, techniques such as electron beam lithography or nanoimprinting allow nanoscale resolution, but are traditionally considered costlymore » and slow. Other techniques such as photolithography or soft lithography have characteristics between these extremes. Combining these techniques to fabricate multi-scale or hybrid fluidics allows fundamental biological and chemical questions can be answered. In this study, a combination of photolithography and electron beam lithography are used to produce two multi-scale fluidic devices that incorporate porous membranes into complex fluidic networks to control the flow of energy, information, and materials in chemical form. In the first device, materials and energy were used to support chemical reactions. A nanoporous membrane fabricated with e-beam lithography separates two parallel, serpentine channels. Photolithography was used to write microfluidic channels around the membrane. The pores were written at 150nm and reduced in size with silicon dioxide deposition from plasma enhanced chemical vapor deposition (PECVD) and atomic layer deposition (ALD). Using this method, the molecular weight cutoff (MWCO) of the membrane can be adapted to the system of interest. In the second approach, photolithography was used to fabricate 200nm thin pores. The pores confined microbes and allowed energy replenishment from a media perfusion channel. The same device can be used for study of intercellular communication via the secretion and uptake of signal molecules. Pore size was tested with 750nm fluorescent polystyrene beads and fluorescein dye. The 200nm PDMS pores were shown to be robust enough to hold 750nm beads while under pressure, but allow fluorescein to diffuse across the barrier. Further testing showed that extended culture of bacteria within the chambers was possible. Finally, these two examples show how lithographically defined porous membranes can be adapted to two unique situations and used to tune the flow of chemical energy, materials, and information within a microfluidic network.« less

Bead-Based Microfluidic Sediment Analogues: Fabrication and Colloid Transport.

PubMed

Guo, Yang; Huang, Jingwei; Xiao, Feng; Yin, Xiaolong; Chun, Jaehun; Um, Wooyong; Neeves, Keith B; Wu, Ning

2016-09-13

Mobile colloids can act as carriers for low-solubility contaminants in the environment. However, the dominant mechanism for this colloid-facilitated transport of chemicals is unclear. Therefore, we developed a bead-based microfluidic platform of sediment analogues and measured both single and population transport of model colloids. The porous medium is assembled through a bead-by-bead injection method. This approach has the versatility to build both electrostatically homogeneous and heterogeneous media at the pore scale. A T-junction at the exit also allowed for encapsulation and enumeration of colloids effluent at single particle resolution to give population dynamics. Tortuosity calculated from pore-scale trajectory analysis and its comparison with lattice Boltzmann simulations revealed that transport of colloids was influenced by the size exclusion effect. The porous media packed by positively and negatively charged beads into two layers showed distinctive colloidal particle retention and significant remobilization and re-adsorption of particles during water flushing. We demonstrated the potential of our method to fabricate porous media with surface heterogeneities at the pore scale. With both single and population dynamics measurement, our platform has the potential to connect pore-scale and macroscale colloid transport on a lab scale and to quantify the impact of grain surface heterogeneities that are natural in the subsurface environment.

Multiscale Pore Throat Network Reconstruction of Tight Porous Media Constrained by Mercury Intrusion Capillary Pressure and Nuclear Magnetic Resonance Measurements

NASA Astrophysics Data System (ADS)

Xu, R.; Prodanovic, M.

2017-12-01

Due to the low porosity and permeability of tight porous media, hydrocarbon productivity strongly depends on the pore structure. Effective characterization of pore/throat sizes and reconstruction of their connectivity in tight porous media remains challenging. Having a representative pore throat network, however, is valuable for calculation of other petrophysical properties such as permeability, which is time-consuming and costly to obtain by experimental measurements. Due to a wide range of length scales encountered, a combination of experimental methods is usually required to obtain a comprehensive picture of the pore-body and pore-throat size distributions. In this work, we combine mercury intrusion capillary pressure (MICP) and nuclear magnetic resonance (NMR) measurements by percolation theory to derive pore-body size distribution, following the work by Daigle et al. (2015). However, in their work, the actual pore-throat sizes and the distribution of coordination numbers are not well-defined. To compensate for that, we build a 3D unstructured two-scale pore throat network model initialized by the measured porosity and the calculated pore-body size distributions, with a tunable pore-throat size and coordination number distribution, which we further determine by matching the capillary pressure vs. saturation curve from MICP measurement, based on the fact that the mercury intrusion process is controlled by both the pore/throat size distributions and the connectivity of the pore system. We validate our model by characterizing several core samples from tight Middle East carbonate, and use the network model to predict the apparent permeability of the samples under single phase fluid flow condition. Results show that the permeability we get is in reasonable agreement with the Coreval experimental measurements. The pore throat network we get can be used to further calculate relative permeability curves and simulate multiphase flow behavior, which will provide valuable insights into the production optimization and enhanced oil recovery design.

Water Displacement in Oil-Wet Tight Reservoirs by Dynamic Network Simulation

NASA Astrophysics Data System (ADS)

Wang, Y.; Li, M.; Chen, M.

2017-12-01

Pore network simulation is an effective tool for studying the multiphase flow in porous media. Based on the topological information and pore-throat size distribution obtained from the analysis of Scanning Electron Microscope (SEM) and constant-rate mercury injection (CRMI) for tight cores (composed by micro-nano scale throats and micro scale pores), a simple cubic (SC) pore-throat network was built with equilateral triangular cross-section throats and cubic bodies. Rules for oil and water movement and redistribution were devised in accordance with the physics process at pore-throat scale. Water flooding from oil-saturated under irreducible water were simulated by considering the changing displacement rate and viscosity ratio at the slightly oil-wet condition (the static contact angle ranges between π/2 to 2π/3). Different from the double pressure field algorithm, a single pressure field which solved by using successive over relaxation method was used with the flow of irreducible water in corners was ignored while its swilling was take into consideration. Dynamic of displacement fronts, relative permeability curves and residual oil saturation were obtained. It showed that there were obviously snap-off at low capillary number (Nc<10-5) and fingering at high capillary number (Nc<10-4) even at a favorable viscosity ratio (M=1). The magnitude of viscosity ratio effect on relative permeability depended largely on the capillary number, which the effect wasn't noticeable for a high capillary number. For residual oil saturation Sor, it showed that Sor decreased with the increase of capillary number at different viscosity ratio. Changing of residual oil saturation from simulation was in good agreement with the experimental results in a certain range, which indicated that this network model could be used to character the water flooding in tight reservoirs.

Inertial effects during irreversible meniscus reconfiguration in angular pores

NASA Astrophysics Data System (ADS)

Ferrari, Andrea; Lunati, Ivan

2014-12-01

In porous media, the dynamics of the invading front between two immiscible fluids is often characterized by abrupt reconfigurations caused by local instabilities of the interface. As a prototype of these phenomena we consider the dynamics of a meniscus in a corner as it can be encountered in angular pores. We investigate this process in detail by means of direct numerical simulations that solve the Navier-Stokes equations in the pore space and employ the Volume of Fluid method (VOF) to track the evolution of the interface. We show that for a quasi-static displacement, the numerically calculated surface energy agrees well with the analytical solutions that we have derived for pores with circular and square cross sections. However, the spontaneous reconfigurations are irreversible and cannot be controlled by the injection rate: they are characterized by the amount of surface energy that is spontaneously released and transformed into kinetic energy. The resulting local velocities can be orders of magnitude larger than the injection velocity and they induce damped oscillations of the interface that possess their own time scales and depend only on fluid properties and pore geometry. In complex media (we consider a network of cubic pores) reconfigurations are so frequent and oscillations last long enough that increasing inertial effects leads to a different fluid distribution by influencing the selection of the next pore to be invaded. This calls into question simple pore-filling rules based only on capillary forces. Also, we demonstrate that inertial effects during irreversible reconfigurations can influence the work done by the external forces that is related to the pressure drop in Darcy's law. This suggests that these phenomena have to be considered when upscaling multiphase flow because local oscillations of the menisci affect macroscopic quantities and modify the constitutive relationships to be used in macro-scale models. These results can be extrapolated to other interface instabilities that are at the origin of fast pore-scale events, such as Haines jumps, snap-off and coalescence.

Small-scale variability in peatland pore-water biogeochemistry, Hudson Bay Lowland, Canada.

PubMed

Ulanowski, T A; Branfireun, B A

2013-06-01

The Hudson Bay Lowland (HBL) of northern Ontario, Manitoba and Quebec, Canada is the second largest contiguous peatland complex in the world, currently containing more than half of Canada's soil carbon. Recent concerns about the ecohydrological impacts to these large northern peatlands resulting from climate change and resource extraction have catalyzed a resurgence in scientific research into this ecologically important region. However, the sheer size, heterogeneity and elaborate landscape arrangements of this ecosystem raise important questions concerning representative sampling of environmental media for chemical or physical characterization. To begin to quantify such variability, this study assessed the small-scale spatial (1m) and short temporal (21 day) variability of surface pore-water biogeochemistry (pH, dissolved organic carbon, and major ions) in a Sphagnum spp.-dominated, ombrotrophic raised bog, and a Carex spp.-dominated intermediate fen in the HBL. In general, pore-water pH and concentrations of dissolved solutes were similar to previously reported literature values from this region. However, systematic sampling revealed consistent statistically significant differences in pore-water chemistries between the bog and fen peatland types, and large within-site spatiotemporal variability. We found that microtopography in the bog was associated with consistent differences in most biogeochemical variables. Temporal changes in dissolved solute chemistry, particularly base cations (Na(+), Ca(2+) and Mg(2+)), were statistically significant in the intermediate fen, likely a result of a dynamic connection between surficial waters and mineral-rich deep groundwater. In both the bog and fen, concentrations of SO4(2-) showed considerable spatial variability, and a significant decrease in concentrations over the study period. The observed variability in peatland pore-water biogeochemistry over such small spatial and temporal scales suggests that under-sampling in northern peatland environments could lead to erroneous conclusions concerning the abundance and distribution of natural elements and pollutants alike. Copyright © 2013 Elsevier B.V. All rights reserved.

Leaching of Conductive Species: Implications to Measurements of Electrical Resistivity

PubMed Central

Spragg, R; Jones, S; Bu, Y; Lu, Y; Bentz, D; Snyder, K; Weiss, J

2017-01-01

Electrical tests have been used to characterize the microstructure of porous materials, the measured electrical response being determined by the contribution of the microstructure (porosity and tortuosity) and the electrical properties of the solution (conductivity of the pore solution) inside the pores of the material. This study has shown how differences in concentration between the pore solution (i.e., the solution in the pores) and the storage solution surrounding the test specimen leads to significant transport (leaching) of the conductive ionic species between the pore solution and the storage solution. Leaching influences the resistivity of the pore solution, thereby influencing electrical measurements on the bulk material from either a surface or uniaxial bulk resistance test. This paper has three main conclusions: 1.) Leaching of conductive species does occur with concentration gradients and that a diffusion based approach can be used to estimate the time scale associated with this change. 2.) Leaching of ions in the pore solution can influence resistivity measurements, and the ratio of surface to uniaxial resistivity can be used as a method to assess the presence of leaching and 3.) An estimation of the magnitude of leaching for standardized tests of cementitious materials. PMID:28584407

Leaching of Conductive Species: Implications to Measurements of Electrical Resistivity.

PubMed

Spragg, R; Jones, S; Bu, Y; Lu, Y; Bentz, D; Snyder, K; Weiss, J

2017-05-01

Electrical tests have been used to characterize the microstructure of porous materials, the measured electrical response being determined by the contribution of the microstructure (porosity and tortuosity) and the electrical properties of the solution (conductivity of the pore solution) inside the pores of the material. This study has shown how differences in concentration between the pore solution (i.e., the solution in the pores) and the storage solution surrounding the test specimen leads to significant transport (leaching) of the conductive ionic species between the pore solution and the storage solution. Leaching influences the resistivity of the pore solution, thereby influencing electrical measurements on the bulk material from either a surface or uniaxial bulk resistance test. This paper has three main conclusions: 1.) Leaching of conductive species does occur with concentration gradients and that a diffusion based approach can be used to estimate the time scale associated with this change. 2.) Leaching of ions in the pore solution can influence resistivity measurements, and the ratio of surface to uniaxial resistivity can be used as a method to assess the presence of leaching and 3.) An estimation of the magnitude of leaching for standardized tests of cementitious materials.

Pore-network model of evaporation-induced salt precipitation in porous media: The effect of correlations and heterogeneity

NASA Astrophysics Data System (ADS)

Dashtian, Hassan; Shokri, Nima; Sahimi, Muhammad

2018-02-01

Salt transport and precipitation in porous media constitute a set of complex and fascinating phenomena that are of considerable interest to several important problems, ranging from storage of CO2 in geological formations, to soil fertility, and protection of pavements and roads, as well as historical monuments. The phenomena occur at the pore scale and are greatly influenced by the heterogeneity of the pore space morphology. We present a pore-network (PN) model to study the phenomena. Vapor diffusion, capillary effect at the brine-vapor interface, flow of brine, and transport of salt and its precipitation in the pores that plug the pores partially or completely are all accounted for. The drying process is modeled by the invasion percolation, while transport of salt in brine is accounted for by the convective-diffusion equation. We demonstrate that the drying patterns, the clustering and connectivity of the pore throats in which salt precipitation occurs, the saturation distribution, and the drying rate are all strongly dependent upon the pore-size distribution, the correlations among the pore sizes, and the anisotropy of the pore space caused by stratification that most natural porous media contain. In particular, if the strata are more or less parallel to the direction of injection of the gas that dries out the pore space (air, for example) and/or causes salt precipitation (CO2, for example), the drying rate increases significantly. Moreover, salt tends to precipitate in clusters of neighboring pores that are parallel to the open surface of the porous medium.

Pore-scale lattice Boltzmann simulation of micro-gaseous flow considering surface diffusion effect

DOE PAGES

Wang, Junjian; Kang, Qinjun; Chen, Li; ...

2016-11-21

Some recent studies have shown that adsorbed gas and its surface diffusion have profound influence on micro-gaseous flow through organic pores in shale gas reservoirs. Here, a multiple-relaxation-time (MRT) LB model is adopted to estimate the apparent permeability of organic shale and a new boundary condition, which combines Langmuir adsorption theory with Maxwellian diffusive reflection boundary condition, is proposed to capture gas slip and surface diffusion of adsorbed gas. The simulation results match well with previous studies carried out using Molecular Dynamics (MD) and show that Maxwell slip boundary condition fails to characterize gas transport in the near wall regionmore » under the influence of the adsorbed gas. The total molar flux can be either enhanced or reduced depending on variations in adsorbed gas coverage and surface diffusion velocity. The effects of pore width, pressure as well as Langmuir properties on apparent permeability of methane transport in organic pores are further studied. It is found that the surface transport plays a significant role in determining the apparent permeability, and the variation of apparent permeability with pore size and pressure is affected by the adsorption and surface diffusion.« less

Multiscale pore networks and their effect on deformation and transport property alteration associated with hydraulic fracturing

NASA Astrophysics Data System (ADS)

Daigle, Hugh; Hayman, Nicholas; Jiang, Han; Tian, Xiao; Jiang, Chunbi

2017-04-01

Multiple lines of evidence indicate that, during a hydraulic fracture stimulation, the permeability of the unfractured matrix far from the main, induced tensile fracture increases by one to two orders of magnitude. This permeability enhancement is associated with pervasive shear failure in a large region surrounding the main induced fracture. We have performed low-pressure gas sorption, mercury intrusion, and nuclear magnetic resonance measurements along with high-resolution scanning electron microscope imaging on several preserved and unpreserved shale samples from North American basins before and after inducing failure in confined compressive strength tests. We have observed that the pore structure in intact samples exhibits multiscale behavior, with sub-micron-scale pores in organic matter connected in isolated, micron-scale clusters which themselves are connected to each other through a network of microcracks. The organic-hosted pore networks are poorly connected due to a significant number of dead-end pores within the organic matter. Following shear failure, we often observe an increase in pore volume in the sub-micron range, which appears to be related to the formation of microcracks that propagate along grain boundaries and other planes of mechanical strength contrast. This is consistent with other experimental and field evidence. In some cases these microcracks cross or terminate in organic matter, intersecting the organic-hosted pores. The induced microcrack networks typically have low connectivity and do not appreciably increase the connectivity of the overall pore network. However, in other cases the shear deformation results in an overall pore volume decrease; samples which exhibit this behavior tend to have more clay minerals. Our interpretation of these phenomena is as follows. As organic matter is converted to hydrocarbons, organic-hosted pores develop, and the hydrocarbons contained in these pores are overpressured. The disconnected nature of these clusters of organic-hosted pores prevents the overpressure from dissipating, resulting in localized overpressure at the micron scale. When the rock is subjected to a hydraulic fracture stimulation, the rock surrounding the main induced fracture experiences shear deformation. Those parts of the rock that contain overpressured fluids in the organic-hosted pores will be more likely to experience dilatancy in the form of brittle deformation; the portions of the rock lacking in organic-hosted pores will tend to experience compactive shear failure since the effective normal stresses are larger. The microcrack networks that propagate into the regions of organic-hosted porosity allow the hydrocarbons resident in those pores to migrate to the main induced tensile fractures. The disconnected nature of the microcrack networks causes only a slight increase in permeability, which is consistent with other observations. Our work illustrates how multiscale pore networks in shale interact with in situ stresses to affect the bulk shale rheology.

Flow and Transport in Complex Microporous Carbonates as a Consequence of Separation of Scales

NASA Astrophysics Data System (ADS)

Bijeljic, B.; Raeini, A. Q.; Lin, Q.; Blunt, M. J.

2017-12-01

Some of the most important examples of flow and transport in complex pore structures are found in subsurface applications such as contaminant hydrology, carbon storage and enhanced oil recovery. Carbonate rock structures contain most of the world's oil reserves, considerable amount of water reserves, and potentially hold a storage capacity for carbon dioxide. However, this type of pore space is difficult to represent due to complexities associated with a wide range of pore sizes and variation in connectivity which poses a considerable challenge for quantitative predictions of transport across multiple scales.A new concept unifying X-ray tomography experiment and direct numerical simulation has been developed that relies on full description flow and solute transport at the pore scale. Differential imaging method (Lin et al. 2016) provides rich information in microporous space, while advective and diffusive mass transport are simulated on micro-CT images of pore-space: Navier-Stokes equations are solved for flow in the image voxels comprising the pore space, streamline-based simulation is used to account for advection, and diffusion is superimposed by random walk.Quantitative validation has been done on analytical solutions for diffusion and by comparing the model predictions versus the experimental NMR measurements in the dual porosity beadpack. Furthermore, we discriminate signatures of multi-scale transport behaviour for a range of carbonate rock (Figure 1), dependent on the heterogeneity of the inter- and intra-grain pore space, heterogeneity in the flow field, and the mass transfer characteristics of the porous media. Finally, we demonstrate the predictive capabilities of the model through an analysis that includes a number of probability density functions flow and transport (PDFs) measures of non-Fickian transport on the micro-CT i935mages. In complex porous media separation of scales exists, leading to flow and transport signatures that need to be described by multiple functions with distinct flow field and transport characteristics. Reference: Lin, Q., Al-Khulaifi Y., Blunt, M.J. and Bijeljic B. (2016). Advances in Water Resources, 96, 306-322, doi:10.1016/j.advwatres.2016.08.002.

Evolution of the pore structure during the early stages of the alkali-activation reaction: An in situ small-angle neutron scattering investigation

DOE PAGES

White, Claire E.; Olds, Daniel P.; Hartl, Monika; ...

2017-02-01

The long-term durability of cement-based materials is influenced by the pore structure and associated permeability at the sub-micrometre length scale. With the emergence of new types of sustainable cements in recent decades, there is a pressing need to be able to predict the durability of these new materials, and therefore nondestructive experimental techniques capable of characterizing the evolution of the pore structure are increasingly crucial for investigating cement durability. Here, small-angle neutron scattering is used to analyze the evolution of the pore structure in alkali-activated materials over the initial 24 h of reaction in order to assess the characteristic poremore » sizes that emerge during these short time scales. By using a unified fitting approach for data modeling, information on the pore size and surface roughness is obtained for a variety of precursor chemistries and morphologies (metakaolin- and slag-based pastes). Furthermore, the impact of activator chemistry is elucidatedviathe analysis of pastes synthesized using hydroxide- and silicate-based activators. It is found that the main aspect influencing the size of pores that are accessible using small-angle neutron scattering analysis (approximately 10–500 Å in diameter) is the availability of free silica in the activating solution, which leads to a more refined pore structure with smaller average pore size. Furthermore, as the reaction progresses the gel pores visible using this scattering technique are seen to increase in size.« less

Understanding hydraulic fracturing: a multi-scale problem.

PubMed

Hyman, J D; Jiménez-Martínez, J; Viswanathan, H S; Carey, J W; Porter, M L; Rougier, E; Karra, S; Kang, Q; Frash, L; Chen, L; Lei, Z; O'Malley, D; Makedonska, N

2016-10-13

Despite the impact that hydraulic fracturing has had on the energy sector, the physical mechanisms that control its efficiency and environmental impacts remain poorly understood in part because the length scales involved range from nanometres to kilometres. We characterize flow and transport in shale formations across and between these scales using integrated computational, theoretical and experimental efforts/methods. At the field scale, we use discrete fracture network modelling to simulate production of a hydraulically fractured well from a fracture network that is based on the site characterization of a shale gas reservoir. At the core scale, we use triaxial fracture experiments and a finite-discrete element model to study dynamic fracture/crack propagation in low permeability shale. We use lattice Boltzmann pore-scale simulations and microfluidic experiments in both synthetic and shale rock micromodels to study pore-scale flow and transport phenomena, including multi-phase flow and fluids mixing. A mechanistic description and integration of these multiple scales is required for accurate predictions of production and the eventual optimization of hydrocarbon extraction from unconventional reservoirs. Finally, we discuss the potential of CO2 as an alternative working fluid, both in fracturing and re-stimulating activities, beyond its environmental advantages.This article is part of the themed issue 'Energy and the subsurface'. © 2016 The Author(s).

Understanding hydraulic fracturing: a multi-scale problem

PubMed Central

Hyman, J. D.; Jiménez-Martínez, J.; Viswanathan, H. S.; Carey, J. W.; Porter, M. L.; Rougier, E.; Karra, S.; Kang, Q.; Frash, L.; Chen, L.; Lei, Z.; O’Malley, D.; Makedonska, N.

2016-01-01

Despite the impact that hydraulic fracturing has had on the energy sector, the physical mechanisms that control its efficiency and environmental impacts remain poorly understood in part because the length scales involved range from nanometres to kilometres. We characterize flow and transport in shale formations across and between these scales using integrated computational, theoretical and experimental efforts/methods. At the field scale, we use discrete fracture network modelling to simulate production of a hydraulically fractured well from a fracture network that is based on the site characterization of a shale gas reservoir. At the core scale, we use triaxial fracture experiments and a finite-discrete element model to study dynamic fracture/crack propagation in low permeability shale. We use lattice Boltzmann pore-scale simulations and microfluidic experiments in both synthetic and shale rock micromodels to study pore-scale flow and transport phenomena, including multi-phase flow and fluids mixing. A mechanistic description and integration of these multiple scales is required for accurate predictions of production and the eventual optimization of hydrocarbon extraction from unconventional reservoirs. Finally, we discuss the potential of CO2 as an alternative working fluid, both in fracturing and re-stimulating activities, beyond its environmental advantages. This article is part of the themed issue ‘Energy and the subsurface’. PMID:27597789

Pore size distribution and accessible pore size distribution in bituminous coals

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sakurovs, Richard; He, Lilin; Melnichenko, Yuri B

2012-01-01

The porosity and pore size distribution of coals determine many of their properties, from gas release to their behavior on carbonization, and yet most methods of determining pore size distribution can only examine a restricted size range. Even then, only accessible pores can be investigated with these methods. Small-angle neutron scattering (SANS) and ultra small-angle neutron scattering (USANS) are increasingly used to characterize the size distribution of all of the pores non-destructively. Here we have used USANS/SANS to examine 24 well-characterized bituminous and subbituminous coals: three from the eastern US, two from Poland, one from New Zealand and the restmore » from the Sydney and Bowen Basins in Eastern Australia, and determined the relationships of the scattering intensity corresponding to different pore sizes with other coal properties. The range of pore radii examinable with these techniques is 2.5 nm to 7 {micro}m. We confirm that there is a wide range of pore sizes in coal. The pore size distribution was found to be strongly affected by both rank and type (expressed as either hydrogen or vitrinite content) in the size range 250 nm to 7 {micro}m and 5 to 10 nm, but weakly in intermediate regions. The results suggest that different mechanisms control coal porosity on different scales. Contrast-matching USANS and SANS were also used to determine the size distribution of the fraction of the pores in these coals that are inaccessible to deuterated methane, CD{sub 4}, at ambient temperature. In some coals most of the small ({approx} 10 nm) pores were found to be inaccessible to CD{sub 4} on the time scale of the measurement ({approx} 30 min - 16 h). This inaccessibility suggests that in these coals a considerable fraction of inherent methane may be trapped for extended periods of time, thus reducing the effectiveness of methane release from (or sorption by) these coals. Although the number of small pores was less in higher rank coals, the fraction of total pores that was inaccessible was not rank dependent. In the Australian coals, at the 10 nm to 50 nm size scales the pores in inertinites appeared to be completely accessible to CD{sub 4}, whereas the pores in the vitrinite were about 75% inaccessible. Unlike the results for total porosity that showed no regional effects on relationships between porosity and coal properties, clear regional differences in the relationships between fraction of closed porosity and coal properties were found. The 10 to 50 nm-sized pores of inertinites of the US and Polish coals examined appeared less accessible to methane than those of the inertinites of Australian coals. This difference in pore accessibility in inertinites may explain why empirical relationships between fluidity and coking properties developed using Carboniferous coals do not apply to Australian coals.« less

Probing the Dynamics of Biomineralization at the Pore Scale Using X-ray Computed Tomography

NASA Astrophysics Data System (ADS)

Armstrong, R. T.; Ajo Franklin, J. B.

2009-12-01

Biomineralization is a natural subsurface process that upon stimulation can dramatically affect soil mechanics and hydraulics. This work presents the results of a study where synchrotron based X-Ray Computed Microtomography (CMT) is used to investigate temporal cementation dynamics and the spatial distribution of biogenic CaCO3 at the pore-scale, thus, shedding light on pore clogging and contact cementation. To facilitate these studies we have developed a family of flow-through bioreactors (ID 8 mm) which can be scanned continuously during precipitation experiments. The reactor is also equipped with differential pressure transducers to allow measurement of sample permeability. Porosity permeability correlations, cementation morphology, CaCO3 spatial distribution, and bulk cementation are addressed herein. Sporosarcina pasteurii (formally Bacillus pasteurii), our model organism, is a prevalent aerobic, motile, soil microbe with a very active urease enzyme. Hydrolysis of urea by the urease enzyme generates carbonate ions, ammonium and an increase in pH which favors carbonate precipitation if appropriate metal cations (e.g. Ca2+) are available. Brightfield microscope results show that precipitation occurs within close proximity of the cell membrane reducing microbial motility and forming a CaCO3 precipitate with a "fluffy" appearance. Besides providing an aqueous environment favorable for mineralization S. pasteurii also provides nucleation sites on its cell membrane. Since this microbe is very effective at inducing carbonate precipitation over a relativity short time span (2-3 days), it was used exclusively in our experiments. Prior to CMT imaging the feasibility of temporal imaging was investigated. Viable cell counts taken before and after imaging showed that a considerable amount of bacteria survived the monochromatic (30 KeV) X-ray exposure. Cementation experiments initiated with inoculation of the CMT column with microbes and urea media, cells were allowed to attach to particle surfaces, then subjected to sequential cementation treatments of urea media and calcium chloride. Current results indicate a morphological difference in formed CaCO3 depending on microbial acclimation to the system (i.e. surface attached or free floating microbes) and CaCO3 spatial arrangements within the porous matrix (i.e. pore necks or pore bodies). Our initial studies indicate that synchrotron CMT will be a powerful tool for pore-scale monitoring of biomineralization, a process relevant to geological carbon sequestration, bioremediation, enhanced oil recovery, slope stability and etc.

FINAL REPORT: Mechanistically-Base Field Scale Models of Uranium Biogeochemistry from Upscaling Pore-Scale Experiments and Models

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wood, Brian D.

2013-11-04

Biogeochemical reactive transport processes in the subsurface environment are important to many contemporary environmental issues of significance to DOE. Quantification of risks and impacts associated with environmental management options, and design of remediation systems where needed, require that we have at our disposal reliable predictive tools (usually in the form of numerical simulation models). However, it is well known that even the most sophisticated reactive transport models available today have poor predictive power, particularly when applied at the field scale. Although the lack of predictive ability is associated in part with our inability to characterize the subsurface and limitations inmore » computational power, significant advances have been made in both of these areas in recent decades and can be expected to continue. In this research, we examined the upscaling (pore to Darcy and Darcy to field) the problem of bioremediation via biofilms in porous media. The principle idea was to start with a conceptual description of the bioremediation process at the pore scale, and apply upscaling methods to formally develop the appropriate upscaled model at the so-called Darcy scale. The purpose was to determine (1) what forms the upscaled models would take, and (2) how one might parameterize such upscaled models for applications to bioremediation in the field. We were able to effectively upscale the bioremediation process to explain how the pore-scale phenomena were linked to the field scale. The end product of this research was to produce a set of upscaled models that could be used to help predict field-scale bioremediation. These models were mechanistic, in the sense that they directly incorporated pore-scale information, but upscaled so that only the essential features of the process were needed to predict the effective parameters that appear in the model. In this way, a direct link between the microscale and the field scale was made, but the upscaling process helped inform potential users of the model what kinds of information would be needed to accurately characterize the system.« less

Persistent Homology fingerprinting of microstructural controls on larger-scale fluid flow in porous media

NASA Astrophysics Data System (ADS)

Moon, C.; Mitchell, S. A.; Callor, N.; Dewers, T. A.; Heath, J. E.; Yoon, H.; Conner, G. R.

2017-12-01

Traditional subsurface continuum multiphysics models include useful yet limiting geometrical assumptions: penny- or disc-shaped cracks, spherical or elliptical pores, bundles of capillary tubes, cubic law fracture permeability, etc. Each physics (flow, transport, mechanics) uses constitutive models with an increasing number of fit parameters that pertain to the microporous structure of the rock, but bear no inter-physics relationships or self-consistency. Recent advances in digital rock physics and pore-scale modeling link complex physics to detailed pore-level geometries, but measures for upscaling are somewhat unsatisfactory and come at a high computational cost. Continuum mechanics rely on a separation between small scale pore fluctuations and larger scale heterogeneity (and perhaps anisotropy), but this can break down (particularly for shales). Algebraic topology offers powerful mathematical tools for describing a local-to-global structure of shapes. Persistent homology, in particular, analyzes the dynamics of topological features and summarizes into numeric values. It offers a roadmap to both "fingerprint" topologies of pore structure and multiscale connectedness as well as links pore structure to physical behavior, thus potentially providing a means to relate the dependence of constitutive behaviors of pore structures in a self-consistent way. We present a persistence homology (PH) analysis framework of 3D image sets including a focused ion beam-scanning electron microscopy data set of the Selma Chalk. We extract structural characteristics of sampling volumes via persistence homology and fit a statistical model using the summarized values to estimate porosity, permeability, and connectivity—Lattice Boltzmann methods for single phase flow modeling are used to obtain the relationships. These PH methods allow for prediction of geophysical properties based on the geometry and connectivity in a computationally efficient way. Sandia National Laboratories is a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia LLC, a wholly owned subsidiary of Honeywell International Inc. for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-NA0003525.

Porosity inside a metal casting

NASA Technical Reports Server (NTRS)

2003-01-01

Pores and voids often form in metal castings on Earth (above) making them useless. A transparent material that behaves at a large scale in microgravity the way that metals behave at the microscopic scale on Earth, will help show how voids form and learn how to prevent them. Scientists are using the microgravity environment on the International Space Station to study how these bubbles form, move and interact. The Pore Formation and Mobility Investigation (PFMI) in the Microgravity Science Glovebox aboard the International Space Station uses a transparent material called succinonitrile that behaves like a metal to study this problem. Video images sent to the ground allow scientists to watch the behavior of the bubbles as they control the melting and freezing of the material. The bubbles do not float to the top of the material in microgravity, so they can study their interactions.

Material Science

NASA Image and Video Library

2003-01-22

Pores and voids often form in metal castings on Earth (above) making them useless. A transparent material that behaves at a large scale in microgravity the way that metals behave at the microscopic scale on Earth, will help show how voids form and learn how to prevent them. Scientists are using the microgravity environment on the International Space Station to study how these bubbles form, move and interact. The Pore Formation and Mobility Investigation (PFMI) in the Microgravity Science Glovebox aboard the International Space Station uses a transparent material called succinonitrile that behaves like a metal to study this problem. Video images sent to the ground allow scientists to watch the behavior of the bubbles as they control the melting and freezing of the material. The bubbles do not float to the top of the material in microgravity, so they can study their interactions.

Pore-scale Simulation and Imaging of Multi-phase Flow and Transport in Porous Media (Invited)

NASA Astrophysics Data System (ADS)

Crawshaw, J.; Welch, N.; Daher, I.; Yang, J.; Shah, S.; Grey, F.; Boek, E.

2013-12-01

We combine multi-scale imaging and computer simulation of multi-phase flow and reactive transport in rock samples to enhance our fundamental understanding of long term CO2 storage in rock formations. The imaging techniques include Confocal Laser Scanning Microscopy (CLSM), micro-CT and medical CT scanning, with spatial resolutions ranging from sub-micron to mm respectively. First, we report a new sample preparation technique to study micro-porosity in carbonates using CLSM in 3 dimensions. Second, we use micro-CT scanning to generate high resolution 3D pore space images of carbonate and cap rock samples. In addition, we employ micro-CT to image the processes of evaporation in fractures and cap rock degradation due to exposure to CO2 flow. Third, we use medical CT scanning to image spontaneous imbibition in carbonate rock samples. Our imaging studies are complemented by computer simulations of multi-phase flow and transport, using the 3D pore space images obtained from the scanning experiments. We have developed a massively parallel lattice-Boltzmann (LB) code to calculate the single phase flow field in these pore space images. The resulting flow fields are then used to calculate hydrodynamic dispersion using a novel scheme to predict probability distributions for molecular displacements using the LB method and a streamline algorithm, modified for optimal solid boundary conditions. We calculate solute transport on pore-space images of rock cores with increasing degree of heterogeneity: a bead pack, Bentheimer sandstone and Portland carbonate. We observe that for homogeneous rock samples, such as bead packs, the displacement distribution remains Gaussian with time increasing. In the more heterogeneous rocks, on the other hand, the displacement distribution develops a stagnant part. We observe that the fraction of trapped solute increases from the beadpack (0 %) to Bentheimer sandstone (1.5 %) to Portland carbonate (8.1 %), in excellent agreement with PFG-NMR experiments. We then use our preferred multi-phase model to directly calculate flow in pore space images of two different sandstones and observe excellent agreement with experimental relative permeabilities. Also we calculate cluster size distributions in good agreement with experimental studies. Our analysis shows that the simulations are able to predict both multi-phase flow and transport properties directly on large 3D pore space images of real rocks. Pore space images, left and velocity distributions, right (Yang and Boek, 2013)

Morphology of the pore space in claystones - evidence from BIB/FIB ion beam sectioning and cryo-SEM observations

NASA Astrophysics Data System (ADS)

Desbois, G.; Urai, J. L.; Kukla, P. A.

2009-12-01

Mudrocks and clay-rich fault gouges are important mechanical elements in the Earth’s crust and form seals for crustal fluids such as groundwater and hydrocarbons. Other fields of interest are the storage of anthropogenic carbon dioxide and radioactive waste in geologic formations. In addition, coupled flows, capillary processes, and associated deformation are of importance in many applied fields. A key factor to understanding these processes is a detailed understanding of the morphology of the pore space. Classic studies of porosity in fine grained materials are performed on dried or freeze dried samples and include metal injection methods, magnetic susceptibility measurement, SEM and TEM imaging, neutron scattering, NMR spectroscopy, and ESEM. Confocal microscopy and X-ray tomography are used to image porosity in coarse grained sediments but the resolution of these techniques is not sufficient at present for applications to mudrocks or clay-rich fault gouges. Therefore, observations and interpretations remain difficult because none of these approaches is able to directly describe the in-situ porosity at the pore scale. In addition, some methods require dried samples in which the natural structure of pores may have been damaged to some extent due to desiccation and dehydration of the clay minerals. A recently developed alternative is to study wet samples using a cryo-SEM, which allows stabilization of wet media at cryo-temperature, in-situ sample preparation by ion beam cross-sectioning (BIB, FIB) and observations of the stabilized microstructure at high resolution. We report on a study of Boom clay from a proposed disposal site of radioactive waste (Mol site, Belgium) using cryo-SEM at cryogenic temperature, with ion beam cross-sectioning to prepare smooth, damage free surfaces. Pores commonly have crack-like tips, preferred orientation parallel to bedding and power law size distribution. We define a number of pore types depending on shape and location in the microstructure. 3-D reconstruction by serial cross-sectioning shows 3-D connectivity of the pore space. These findings offer a new insight into the morphology of pores down to nano-scale and provide the basis for microstructure-based models of transport in clays. SEM image (SE) of a Broad Ion Beam polished cross-section performed on dry Boom clay (Mol site, Belgium) showing the 2D apparent porosity (26.3%). The cross-section is perpendicular to the bedding.

Removal of bacteriophages with different surface charges by diverse ceramic membrane materials in pilot spiking tests.

PubMed

Hambsch, B; Bösl, M; Eberhagen, I; Müller, U

2012-01-01

This study examines mechanisms for removal of bacteriophages (MS2 and phiX174) by ceramic membranes without application of flocculants. The ceramic membranes considered included ultra- and microfiltration membranes of different materials. Phages were spiked into the feed water in pilot scale tests in a waterworks. The membranes with pore sizes of 10 nm provided a 2.5-4.0 log removal of the phages. For pore sizes of 50 nm, the log removal dropped to 0.96-1.8. The membrane with a pore size of 200 nm did not remove phages. So, the removal of both MS2- and phiX174-phages depended on the pore size of the membranes. But apart from pore size also other factors influence the removal of phages. Removal was 0.5-0.9 log higher for MS2-phages compared with phiX174-phages. Size exclusion seems to be the major but not the only mechanism which influences the efficiency of phage removal by ceramic membranes.

Spatially resolved D-T(2) correlation NMR of porous media.

PubMed

Zhang, Yan; Blümich, Bernhard

2014-05-01

Within the past decade, 2D Laplace nuclear magnetic resonance (NMR) has been developed to analyze pore geometry and diffusion of fluids in porous media on the micrometer scale. Many objects like rocks and concrete are heterogeneous on the macroscopic scale, and an integral analysis of microscopic properties provides volume-averaged information. Magnetic resonance imaging (MRI) resolves this spatial average on the contrast scale set by the particular MRI technique. Desirable contrast parameters for studies of fluid transport in porous media derive from the pore-size distribution and the pore connectivity. These microscopic parameters are accessed by 1D and 2D Laplace NMR techniques. It is therefore desirable to combine MRI and 2D Laplace NMR to image functional information on fluid transport in porous media. Because 2D Laplace resolved MRI demands excessive measuring time, this study investigates the possibility to restrict the 2D Laplace analysis to the sum signals from low-resolution pixels, which correspond to pixels of similar amplitude in high-resolution images. In this exploratory study spatially resolved D-T2 correlation maps from glass beads and mortar are analyzed. Regions of similar contrast are first identified in high-resolution images to locate corresponding pixels in low-resolution images generated with D-T2 resolved MRI for subsequent pixel summation to improve the signal-to-noise ratio of contrast-specific D-T2 maps. This method is expected to contribute valuable information on correlated sample heterogeneity from the macroscopic and the microscopic scales in various types of porous materials including building materials and rock. Copyright © 2014 Elsevier Inc. All rights reserved.

Multi-scale mechanical response of freeze-dried collagen scaffolds for tissue engineering applications.

PubMed

Offeddu, Giovanni S; Ashworth, Jennifer C; Cameron, Ruth E; Oyen, Michelle L

2015-02-01

Tissue engineering has grown in the past two decades as a promising solution to unresolved clinical problems such as osteoarthritis. The mechanical response of tissue engineering scaffolds is one of the factors determining their use in applications such as cartilage and bone repair. The relationship between the structural and intrinsic mechanical properties of the scaffolds was the object of this study, with the ultimate aim of understanding the stiffness of the substrate that adhered cells experience, and its link to the bulk mechanical properties. Freeze-dried type I collagen porous scaffolds made with varying slurry concentrations and pore sizes were tested in a viscoelastic framework by macroindentation. Membranes made up of stacks of pore walls were indented using colloidal probe atomic force microscopy. It was found that the bulk scaffold mechanical response varied with collagen concentration in the slurry consistent with previous studies on these materials. Hydration of the scaffolds resulted in a more compliant response, yet lesser viscoelastic relaxation. Indentation of the membranes suggested that the material making up the pore walls remains unchanged between conditions, so that the stiffness of the scaffolds at the scale of seeded cells is unchanged; rather, it is suggested that thicker pore walls or more of these result in the increased moduli for the greater slurry concentration conditions. Copyright © 2014 The Authors. Published by Elsevier Ltd.. All rights reserved.

Final report of “A Detailed Study of the Physical Mechanisms Controlling CO2-Brine Capillary Trapping in the Subsurface” (University of Arizona, DE-SC0006696)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schaap, Marcel G.

Carbon capture and storage (CCS) of carbon dioxide emissions generated by production or combustion of fossil fuels is a technologically viable means to reduce the build-up of CO2 in the atmosphere and oceans. Using advantages of scale and location, CCS is particularly suitable for large point sources near ubiquitous deep saline aquifers, depleted gas reservoirs, or at production reservoirs for enhanced oil recovery (EOR). In the BES-funded research project, Oregon State University (OSU) carried out capillary trapping experiments with proxy fluids that mimic the properties of the scCO2/brine system under ambient temperatures and pressures, and successfully developed a unique andmore » novel x-ray compatible, high-pressure, elevated temperature setup to study the scCO2/brine system under challenging reservoir conditions. Both methodologies were applied to a variety of porous media, including synthetic (glass bead) and geologic (Bentheimer sandstone) materials. The University of Arizona (UA) developed pore-scale lattice Boltzmann (LB) models which are able to handle the experimental conditions for proxy fluids, as well as the scCO2/brine system, that are capable of simulating permeability in volumes of tens of millions of fluid elements. We reached the following summary findings (main institute indicated): 1. (OSU/UA) To understand capillary trapping in a multiphase fluid-porous medium system, the system must be analyzed from a pore-scale force balance perspective; trapping can be enhanced by manipulating wetting and nonwetting phase fluid properties. 2. (OSU) Pore-scale fluid connectivity and topology has a clear and direct effect on nonwetting phase capillary trapping efficiency. 3. (OSU) Rock type and flow regime also have a pronounced effects on capillary trapping. 4. (OSU/UA) There is a predictable relationship between NWP connectivity and NWP saturation, which allows for development of injection strategies that optimize trapping. The commonly used Land model (Land, 1968) does not predict amount of trapped NWP accurately. 5. (UA) There are ambiguities regarding the segmentation of large-volume gray-scale CT data into pore-volumes suitable for pore-scale modeling. Simulated permeabilities vary by three orders of magnitude and do not resemble observed values very well. Small-volume synchrotron-based CT data (such as produced by OSU) does not suffer significantly from segmentation ambiguities. 6. (UA) A standard properly parameterized Shan-Chen model LB model is useful for simulating porous media with proxy fluids as well as the scCO2/brine system and produces results that are consistent with tomographic observations. 7. (UA) A LB model with fluid-interactions defined by a (modified) Peng-Robinson Equation of State is able to handle the scCO2/brine system with variable solid phase wettability. This model is numerically stable at temperatures between 0 and 250 °C and pressures between 3 and 50 MPa, and produces appropriate densities above the critical point of CO2 and exhibits three-phase separation below. Based on above findings OSU and UA have proposed continued experimentation and pore-scale modeling of the scCO2/brine system. The reported research has extensively covered capillary trapping using proxy fluids, but due to limited beam-time availability we were unable to apply our high-pressure CO2 setup to sufficient variation in fluid properties, and initial scCO2 connectivity. New data will also allow us to test, calibrate and apply our LB models to reservoir conditions beyond those that are currently feasible experimentally. Such experiments and simulations will also allow us to provide information how suitable proxy fluids are for the scCO2/brine system. We believe it would be worthwhile to pursue the following new research questions: 1. What are the fundamental differences in the physics underlying capillary trapping at ambient vs. supercritical conditions? 2. Do newly developed pore-scale trapping interactions and relationships translate to continuum scales? A motivation for these questions was elaborated in “Capillary Trapping of Super-Critical CO2: Linking Pore and Continuum Scales to Verify new Relationships” that was submitted to DOE-BES in 2015.« less

Computational and Experimental Studies of Microstructure-Scale Porosity in Metallic Fuels for Improved Gas Swelling Behavior

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mllett, Paul; McDeavitt, Sean; Deo, Chaitanya

This proposal will investigate the stability of bimodal pore size distributions in metallic uranium and uranium-zirconium alloys during sintering and re-sintering annealing treatments. The project will utilize both computational and experimental approaches. The computational approach includes both Molecular Dynamics simulations to determine the self-diffusion coefficients in pure U and U-Zr alloys in single crystals, grain boundaries, and free surfaces, as well as calculations of grain boundary and free surface interfacial energies. Phase-field simulations using MOOSE will be conducted to study pore and grain structure evolution in microstructures with bimodal pore size distributions. Experiments will also be performed to validate themore » simulations, and measure the time-dependent densification of bimodal porous compacts.« less

Insights into the role of wettability in cathode catalyst layer of proton exchange membrane fuel cell; pore scale immiscible flow and transport processes

NASA Astrophysics Data System (ADS)

Fathi, H.; Raoof, A.; Mansouri, S. H.

2017-05-01

The production of liquid water in cathode catalyst layer, CCL, is a significant barrier to increase the efficiency of proton exchange membrane fuel cell. Here we present, for the first time, a direct three-dimensional pore-scale modelling to look at the complex immiscible two-phase flow in CCL. After production of the liquid water at the surface of CCL agglomerates due to the electrochemical reactions, water spatial distribution affects transport of oxygen through the CCL as well as the rate of reaction at the agglomerate surfaces. To explore the wettability effects, we apply hydrophilic and hydrophobic properties using different surface contact angles. Effective diffusivity is calculated under several water saturation levels. Results indicate larger diffusive transport values for hydrophilic domain compared to the hydrophobic media where the liquid water preferentially floods the larger pores. However, hydrophobic domain showed more available surface area and higher oxygen consumption rate at the reaction sites under various saturation levels, which is explained by the effect of wettability on pore-scale distribution of water. Hydrophobic domain, with a contact angle of 150, reveals efficient water removal where only 28% of the pore space stays saturated. This condition contributes to the enhanced available reaction surface area and oxygen diffusivity.

The role of mesopores in MTBE removal with granular activated carbon.

PubMed

Redding, Adam M; Cannon, Fred S

2014-06-01

This activated carbon research appraised how pore size and empty-bed contact time influenced the removal of methyl tert-butyl ether (MTBE) at part-per-billion (ppb) concentrations when MTBE was the sole organic impurity. The study compared six granular activated carbons (GACs) from three parent sources; these GACs contained a range of pore volume distributions and had uniform slurry pHs of 9.7-10.4 (i.e. the carbons' bulk surface chemistries were basic). Several of these activated carbons had been specifically tailored for enhanced sorption of trace organic compounds. In these tests, MTBE was spiked into deionized-distilled water (∼pH 7); MTBE loading was measured by isotherms and by rapid small-scale column tests (RSSCTs) that simulated full-scale empty-bed contact times of 7, 14, and 28 min. The results showed that both ultra-fine micropores and small-diameter mesopores were important for MTBE adsorption. Specifically, full MTBE loading during RSSCTs bore a strong correlation (R(2) = 0.94) to the product (mL/g × mL/g) of pore volume ≤4.06 Å wide and pore volume between ∼22 Å and ∼59 Å wide. This correlation was greater than for the product of any other pore volume combinations. Also, this product exhibited a stronger correlation than for just one or the other of these two pore ranges. This multiplicative relationship implied that both of these pore sizes were important for the optimum GAC performance of these six carbons (i.e. favorable mass transfer coupled with favorable sorption). The authors also compared MTBE mass loading during RSSCTs (μg MTBE/g GAC) to isotherm capacity (μg MTBE/g GAC). This RSSCT loading "efficiency" ranged from 28% to 96% for the six GACs; this efficiency correlated most strongly to pores that were 14-200 Å wide (R(2) = 0.94). This correlation indicated that only those carbons with a sufficient volume of 14-200 Å pores could adsorb MTBE to the extent that would be predicted from isotherm data. Copyright © 2014 Elsevier Ltd. All rights reserved.

Consideration of grain packing in granular iron treatability studies

NASA Astrophysics Data System (ADS)

Firdous, R.; Devlin, J. F.

2014-08-01

Commercial granular iron (GI) is light steel that is used in Permeable Reactive Barriers (PRBs). Investigations into the reactivity of GI have focused on its chemical nature and relatively little direct work has been done to account for the effects of grain shape and packing. Both of these factors are expected to influence available grain surface area, which is known to correlate to reactivity. Commercial granular iron grains are platy and therefore pack in preferential orientations that could affect solution access to the surface. Three packing variations were investigated using Connelly Iron and trichloroethylene (TCE). Experimental kinetic data showed reaction rates 2-4 times higher when grains were packed with long axes preferentially parallel to flow (VP) compared to packings with long axes preferentially perpendicular to flow (HP) or randomly arranged (RP). The variations were found to be explainable by variations in reactive sorption capacities, i.e., sorption to sites where chemical transformations took place. The possibility that the different reactive sorption capacities were related to physical pore-scale differences was assessed by conducting an image analysis of the pore structure of sectioned columns. The analyses suggested that pore-scale factors - in particular the grain surface availability, reflected in the sorption capacity terms of the kinetic model used - could only account for a fraction of the observed reactivity differences between packing types. It is concluded that packing does affect observable reaction rates but that micro-scale features on the grain surfaces, rather than the pore scale characteristics, account for most of the apparent reactivity differences. This result suggests that treatability tests should consider the packing of columns carefully if they are to mimic field performance of PRBs to the greatest extent possible.

Statistical scaling of geometric characteristics in stochastically generated pore microstructures

DOE PAGES

Hyman, Jeffrey D.; Guadagnini, Alberto; Winter, C. Larrabee

2015-05-21

In this study, we analyze the statistical scaling of structural attributes of virtual porous microstructures that are stochastically generated by thresholding Gaussian random fields. Characterization of the extent at which randomly generated pore spaces can be considered as representative of a particular rock sample depends on the metrics employed to compare the virtual sample against its physical counterpart. Typically, comparisons against features and/patterns of geometric observables, e.g., porosity and specific surface area, flow-related macroscopic parameters, e.g., permeability, or autocorrelation functions are used to assess the representativeness of a virtual sample, and thereby the quality of the generation method. Here, wemore » rely on manifestations of statistical scaling of geometric observables which were recently observed in real millimeter scale rock samples [13] as additional relevant metrics by which to characterize a virtual sample. We explore the statistical scaling of two geometric observables, namely porosity (Φ) and specific surface area (SSA), of porous microstructures generated using the method of Smolarkiewicz and Winter [42] and Hyman and Winter [22]. Our results suggest that the method can produce virtual pore space samples displaying the symptoms of statistical scaling observed in real rock samples. Order q sample structure functions (statistical moments of absolute increments) of Φ and SSA scale as a power of the separation distance (lag) over a range of lags, and extended self-similarity (linear relationship between log structure functions of successive orders) appears to be an intrinsic property of the generated media. The width of the range of lags where power-law scaling is observed and the Hurst coefficient associated with the variables we consider can be controlled by the generation parameters of the method.« less

Pore Formation and Mobility Investigation video images

NASA Technical Reports Server (NTRS)

2003-01-01

Video images sent to the ground allow scientists to watch the behavior of the bubbles as they control the melting and freezing of the material during the Pore Formation and Mobility Investigation (PFMI) in the Microgravity Science Glovebox aboard the International Space Station. While the investigation studies the way that metals behave at the microscopic scale on Earth -- and how voids form -- the experiment uses a transparent material called succinonitrile that behaves like a metal to study this problem. The bubbles do not float to the top of the material in microgravity, so they can study their interactions.

Effects of pore-scale dispersion, degree of heterogeneity, sampling size, and source volume on the concentration moments of conservative solutes in heterogeneous formations

Treesearch

Daniele Tonina; Alberto Bellin

2008-01-01

Pore-scale dispersion (PSD), aquifer heterogeneity, sampling volume, and source size influence solute concentrations of conservative tracers transported in heterogeneous porous formations. In this work, we developed a new set of analytical solutions for the concentration ensemble mean, variance, and coefficient of variation (CV), which consider the effects of all these...

The Backscattering Phase Function for a Sphere with a Two-Scale Relief of Rough Surface

NASA Astrophysics Data System (ADS)

Klass, E. V.

2017-12-01

The backscattering of light from spherical surfaces characterized by one and two-scale roughness reliefs has been investigated. The analysis is performed using the three-dimensional Monte-Carlo program POKS-RG (geometrical-optics approximation), which makes it possible to take into account the roughness of objects under study by introducing local geometries of different levels. The geometric module of the program is aimed at describing objects by equations of second-order surfaces. One-scale roughness is set as an ensemble of geometric figures (convex or concave halves of ellipsoids or cones). The two-scale roughness is modeled by convex halves of ellipsoids, with surface containing ellipsoidal pores. It is shown that a spherical surface with one-scale convex inhomogeneities has a flatter backscattering phase function than a surface with concave inhomogeneities (pores). For a sphere with two-scale roughness, the dependence of the backscattering intensity is found to be determined mostly by the lower-level inhomogeneities. The influence of roughness on the dependence of the backscattering from different spatial regions of spherical surface is analyzed.

A multi-topographical-instrument analysis: the breast implant texture measurement

NASA Astrophysics Data System (ADS)

Garabédian, Charles; Delille, Rémi; Deltombe, Raphaël; Anselme, Karine; Atlan, Michael; Bigerelle, Maxence

2017-06-01

Capsular contracture is a major complication after implant-based breast augmentation. To address this tissue reaction, most manufacturers texture the outer breast implant surfaces with calibrated salt grains. However, the analysis of these surfaces on sub-micron scales has been under-studied. This scale range is of interest to understand the future of silicone particles potentially released from the implant surface and the aetiology of newly reported complications, such as Anaplastic Large Cell Lymphoma. The surface measurements were accomplished by tomography and by two optical devices based on interferometry and on focus variation. The robustness of the measurements was investigated from the tissue scale to the cellular scale. The macroscopic pore-based structure of the textured implant surfaces is consistently measured by the three instruments. However, the multi-scale analyses start to be discrepant in a scale range between 50 µm and 500 µm characteristic of a finer secondary roughness regardless of the pore shape. The focus variation and the micro-tomography would fail to capture this roughness regime because of a focus-related optical artefact and of step-shaped artefact respectively.

Prediction of Gas Injection Performance for Heterogeneous Reservoirs

DOE Office of Scientific and Technical Information (OSTI.GOV)

Blunt, Martin J.; Orr, Franklin M.

This report describes research carried out in the Department of Petroleum Engineering at Stanford University from September 1997 - September 1998 under the second year of a three-year grant from the Department of Energy on the "Prediction of Gas Injection Performance for Heterogeneous Reservoirs." The research effort is an integrated study of the factors affecting gas injection, from the pore scale to the field scale, and involves theoretical analysis, laboratory experiments, and numerical simulation. The original proposal described research in four areas: (1) Pore scale modeling of three phase flow in porous media; (2) Laboratory experiments and analysis of factorsmore » influencing gas injection performance at the core scale with an emphasis on the fundamentals of three phase flow; (3) Benchmark simulations of gas injection at the field scale; and (4) Development of streamline-based reservoir simulator. Each state of the research is planned to provide input and insight into the next stage, such that at the end we should have an integrated understanding of the key factors affecting field scale displacements.« less

Study of pore pressure reaction on hydraulic fracturing

NASA Astrophysics Data System (ADS)

Trimonova, Mariia; Baryshnikov, Nikolay; Turuntaev, Sergey; Zenchenko, Evgeniy; Zenchenko, Petr

2017-04-01

We represent the results of the experimental study of the hydraulic fracture propagation influence on the fluid pore pressure. Initial pore pressure was induced by injection and production wells. The experiments were carried out according to scaling analysis based on the radial model of the fracture. All required geomechanical and hydrodynamical properties of a sample were derived from the scaling laws. So, gypsum was chosen as a sample material and vacuum oil as a fracturing fluid. The laboratory setup allows us to investigate the samples of cylindrical shape. It can be considered as an advantage in comparison with standard cubic samples, because we shouldn't consider the stress field inhomogeneity induced by the corners. Moreover, we can set 3D-loading by this setting. Also the sample diameter is big enough (43cm) for placing several wells: the fracturing well in the center and injection and production wells on two opposite sides of the central well. The experiment consisted of several stages: a) applying the horizontal pressure; b) applying the vertical pressure; c) water solution injection in the injection well with a constant pressure; d) the steady state obtaining; e) the oil injection in the central well with a constant rate. The pore pressure was recorded in the 15 points along bottom side of the sample during the whole experiment. We observe the pore pressure change during all the time of the experiment. First, the pore pressure changed due to water injection. Then we began to inject oil in the central well. We compared the obtained experimental data on the pore pressure changes with the solution of the 2D single-phase equation of pore-elasticity, and we found significant difference. The variation of the equation parameters couldn't help to resolve the discrepancy. After the experiment, we found that oil penetrated into the sample before and after the fracture initiation. This fact encouraged us to consider another physical process - the oil-water displacement. Have taken into account the phenomenon, we could find the parameter values for the best matching the experimental data with the analytical one. After such a comparison, we could estimate the permeability variation in the different directions due to changes in the pore pressure during fracturing. Thus it was found that for the correct solution of hydrodynamic problems in relation with hydraulic fracturing (for example, to estimate the production rate of the fractured well) one should take into account the change of the permeability in the vicinity of the fracture and solve nonlinear pore-elasticity problem.

Methane Recovery from Hydrate-bearing Sediments

DOE Office of Scientific and Technical Information (OSTI.GOV)

J. Carlos Santamarina; Costas Tsouris

2011-04-30

Gas hydrates are crystalline compounds made of gas and water molecules. Methane hydrates are found in marine sediments and permafrost regions; extensive amounts of methane are trapped in the form of hydrates. Methane hydrate can be an energy resource, contribute to global warming, or cause seafloor instability. This study placed emphasis on gas recovery from hydrate bearing sediments and related phenomena. The unique behavior of hydrate-bearing sediments required the development of special research tools, including new numerical algorithms (tube- and pore-network models) and experimental devices (high pressure chambers and micromodels). Therefore, the research methodology combined experimental studies, particle-scale numerical simulations,more » and macro-scale analyses of coupled processes. Research conducted as part of this project started with hydrate formation in sediment pores and extended to production methods and emergent phenomena. In particular, the scope of the work addressed: (1) hydrate formation and growth in pores, the assessment of formation rate, tensile/adhesive strength and their impact on sediment-scale properties, including volume change during hydrate formation and dissociation; (2) the effect of physical properties such as gas solubility, salinity, pore size, and mixed gas conditions on hydrate formation and dissociation, and it implications such as oscillatory transient hydrate formation, dissolution within the hydrate stability field, initial hydrate lens formation, and phase boundary changes in real field situations; (3) fluid conductivity in relation to pore size distribution and spatial correlation and the emergence of phenomena such as flow focusing; (4) mixed fluid flow, with special emphasis on differences between invading gas and nucleating gas, implications on relative gas conductivity for reservoir simulations, and gas recovery efficiency; (5) identification of advantages and limitations in different gas production strategies with emphasis; (6) detailed study of CH4-CO2 exchange as a unique alternative to recover CH4 gas while sequestering CO2; (7) the relevance of fines in otherwise clean sand sediments on gas recovery and related phenomena such as fines migration and clogging, vuggy structure formation, and gas-driven fracture formation during gas production by depressurization.« less

Percolation properties of 3-D multiscale pore networks: how connectivity controls soil filtration processes

NASA Astrophysics Data System (ADS)

Perrier, E. M. A.; Bird, N. R. A.; Rieutord, T. B.

2010-04-01

Quantifying the connectivity of pore networks is a key issue not only for modelling fluid flow and solute transport in porous media but also for assessing the ability of soil ecosystems to filter bacteria, viruses and any type of living microorganisms as well inert particles which pose a contamination risk. Straining is the main mechanical component of filtration processes: it is due to size effects, when a given soil retains a conveyed entity larger than the pores through which it is attempting to pass. We postulate that the range of sizes of entities which can be trapped inside soils has to be associated with the large range of scales involved in natural soil structures and that information on the pore size distribution has to be complemented by information on a Critical Filtration Size (CFS) delimiting the transition between percolating and non percolating regimes in multiscale pore networks. We show that the mass fractal dimensions which are classically used in soil science to quantify scaling laws in observed pore size distributions can also be used to build 3-D multiscale models of pore networks exhibiting such a critical transition. We extend to the 3-D case a new theoretical approach recently developed to address the connectivity of 2-D fractal networks (Bird and Perrier, 2009). Theoretical arguments based on renormalisation functions provide insight into multi-scale connectivity and a first estimation of CFS. Numerical experiments on 3-D prefractal media confirm the qualitative theory. These results open the way towards a new methodology to estimate soil filtration efficiency from the construction of soil structural models to be calibrated on available multiscale data.

Percolation properties of 3-D multiscale pore networks: how connectivity controls soil filtration processes

NASA Astrophysics Data System (ADS)

Perrier, E. M. A.; Bird, N. R. A.; Rieutord, T. B.

2010-10-01

Quantifying the connectivity of pore networks is a key issue not only for modelling fluid flow and solute transport in porous media but also for assessing the ability of soil ecosystems to filter bacteria, viruses and any type of living microorganisms as well inert particles which pose a contamination risk. Straining is the main mechanical component of filtration processes: it is due to size effects, when a given soil retains a conveyed entity larger than the pores through which it is attempting to pass. We postulate that the range of sizes of entities which can be trapped inside soils has to be associated with the large range of scales involved in natural soil structures and that information on the pore size distribution has to be complemented by information on a critical filtration size (CFS) delimiting the transition between percolating and non percolating regimes in multiscale pore networks. We show that the mass fractal dimensions which are classically used in soil science to quantify scaling laws in observed pore size distributions can also be used to build 3-D multiscale models of pore networks exhibiting such a critical transition. We extend to the 3-D case a new theoretical approach recently developed to address the connectivity of 2-D fractal networks (Bird and Perrier, 2009). Theoretical arguments based on renormalisation functions provide insight into multi-scale connectivity and a first estimation of CFS. Numerical experiments on 3-D prefractal media confirm the qualitative theory. These results open the way towards a new methodology to estimate soil filtration efficiency from the construction of soil structural models to be calibrated on available multiscale data.

Pore-scale investigation on stress-dependent characteristics of granular packs and the impact of pore deformation on fluid distribution

DOE PAGES

Yoon, Hongkyu; Klise, Katherine A.; Torrealba, Victor A.; ...

2015-05-25

Understanding the effect of changing stress conditions on multiphase flow in porous media is of fundamental importance for many subsurface activities including enhanced oil recovery, water drawdown from aquifers, soil confinement, and geologic carbon storage. Geomechanical properties of complex porous systems are dynamically linked to flow conditions, but their feedback relationship is often oversimplified due to the difficulty of representing pore-scale stress deformation and multiphase flow characteristics in high fidelity. In this work, we performed pore-scale experiments of single- and multiphase flow through bead packs at different confining pressure conditions to elucidate compaction-dependent characteristics of granular packs and their impactmore » on fluid flow. A series of drainage and imbibition cycles were conducted on a water-wet, soda-lime glass bead pack under varying confining stress conditions. Simultaneously, X-ray micro-CT was used to visualize and quantify the degree of deformation and fluid distribution corresponding with each stress condition and injection cycle. Micro-CT images were segmented using a gradient-based method to identify fluids (e.g., oil and water), and solid phase redistribution throughout the different experimental stages. Changes in porosity, tortuosity, and specific surface area were quantified as a function of applied confining pressure. Results demonstrate varying degrees of sensitivity of these properties to confining pressure, which suggests that caution must be taken when considering scalability of these properties for practical modeling purposes. Changes in capillary number with confining pressure are attributed to the increase in pore velocity as a result of pore contraction. Furthermore, this increase in pore velocity was found to have a marginal impact on average phase trapping at different confining pressures.« less

Lab and Pore-Scale Study of Low Permeable Soils Diffusional Tortuosity

NASA Astrophysics Data System (ADS)

Lekhov, V.; Pozdniakov, S. P.; Denisova, L.

2016-12-01

Diffusion plays important role in contaminant spreading in low permeable units. The effective diffusion coefficient of saturated porous medium depends on this coefficient in water, porosity and structural parameter of porous space - tortuosity. Theoretical models of relationship between porosity and diffusional tortuosity are usually derived for conceptual granular models of medium filled by solid particles of simple geometry. These models usually do not represent soils with complex microstructure. The empirical models, like as Archie's law, based on the experimental electrical conductivity data are mostly useful for practical applications. Such models contain empirical parameters that should be defined experimentally for given soil type. In this work, we compared tortuosity values obtained in lab-scale diffusional experiments and pore scale diffusion simulation for the studied soil microstructure and exanimated relationship between tortuosity and porosity. Samples for the study were taken from borehole cores of low-permeable silt-clay formation. Using the samples of 50 cm3 we performed lab scale diffusional experiments and estimated the lab-scale tortuosity. Next using these samples we studied the microstructure with X-ray microtomograph. Shooting performed on undisturbed microsamples of size 1,53 mm with a resolution ×300 (10243 vox). After binarization of each obtained 3-D structure, its spatial correlation analysis was performed. This analysis showed that the spatial correlation scale of the indicator variogram is considerably smaller than microsample length. Then there was the numerical simulation of the Laplace equation with binary coefficients for each microsamples. The total number of simulations at the finite-difference grid of 1753 cells was 3500. As a result the effective diffusion coefficient, tortuosity and porosity values were obtained for all studied microsamples. The results were analyzed in the form of graph of tortuosity versus porosity. The 6 experimental tortuosity values well agree with pore-scale simulations falling in the general pattern that shows nonlinear decreasing of tortuosity with decreasing of porosity. Fitting this graph by Archie model we found exponent value in the range between 1,8 and 2,4. This work was supported by RFBR via grant 14-05-00409.

A level set method for determining critical curvatures for drainage and imbibition.

PubMed

Prodanović, Masa; Bryant, Steven L

2006-12-15

An accurate description of the mechanics of pore level displacement of immiscible fluids could significantly improve the predictions from pore network models of capillary pressure-saturation curves, interfacial areas and relative permeability in real porous media. If we assume quasi-static displacement, at constant pressure and surface tension, pore scale interfaces are modeled as constant mean curvature surfaces, which are not easy to calculate. Moreover, the extremely irregular geometry of natural porous media makes it difficult to evaluate surface curvature values and corresponding geometric configurations of two fluids. Finally, accounting for the topological changes of the interface, such as splitting or merging, is nontrivial. We apply the level set method for tracking and propagating interfaces in order to robustly handle topological changes and to obtain geometrically correct interfaces. We describe a simple but robust model for determining critical curvatures for throat drainage and pore imbibition. The model is set up for quasi-static displacements but it nevertheless captures both reversible and irreversible behavior (Haines jump, pore body imbibition). The pore scale grain boundary conditions are extracted from model porous media and from imaged geometries in real rocks. The method gives quantitative agreement with measurements and with other theories and computational approaches.

Quantification of Soil Pore Structure Based on Minkowski-Functions

NASA Astrophysics Data System (ADS)

Vogel, H.; Weller, U.; Schlüter, S.

2009-05-01

The porous structure in soils and other geologic media is typically a complex 3-dimensional object. Most of the physical material properties including mechanical and hydraulic characteristics are immediately linked to this structure which can be directly observed using non-invasive techniques as e.g. X-ray tomography. It is an old dream and still a formidable challenge to related structural features of porous media to their physical properties. In this contribution we present a scale-invariant concept to quantify pore structure based on a limited set of meaningful morphological functions. They are based on d+1 Minkowski functionals as defined for d-dimensional bodies. These basic quantities are determined as a function of pore size obtained by filter procedures using mathematical morphology. The resulting Minkowski functions provide valuable information on pore size, pore surface area and pore topology having the potential to be linked to physical properties. The theoretical background and the related algorithms are presented and the approach is demonstrated for the structure of an arable topsoil obtained by X-ray micro tomography. We also discuss the fundamental problem of limited resolution which is critical for any attempt to quantify structural features at any scale.

Membrane properties change in fine-pore aeration diffusers: full-scale variations of transfer efficiency and headloss.

PubMed

Rosso, Diego; Libra, Judy A; Wiehe, Wolfgang; Stenstrom, Michael K

2008-05-01

Fine-pore diffusers are the most common aeration system in municipal wastewater treatment. Punched polymeric membranes are often used in fine-pore aeration due to their advantageous initial performance. These membranes are subject to fouling and scaling, resulting in increased headloss and reduced oxygen transfer efficiency, both contributing to increased plant energy costs. This paper describes and discusses the change in material properties for polymeric fine-pore diffusers, comparing new and used membranes. Three different diffuser technologies were tested and sample diffusers from two wastewater treatment facilities were analysed. The polymeric membranes analysed in this paper were composed of ethylene-propylene-diene monomer (EPDM), polyurethane, and silicon. Transfer efficiency is usually lower with longer times in operation, as older, dilated orifices produce larger bubbles, which are unfavourable to mass transfer. At the same time, headloss increases with time in operation, since membranes increase in rigidity and hardness, and fouling and scaling phenomena occur at the orifice opening. Change in polymer properties and laboratory test results correlate with the decrease in oxygen transfer efficiency.

Pore scale Assessment of Heat and Mass transfer in Porous Medium Using Phase Field Method with Application to Soil Borehole Thermal Storage (SBTES) Systems

NASA Astrophysics Data System (ADS)

Moradi, A.

2015-12-01

To properly model soil thermal performance in unsaturated porous media, for applications such as SBTES systems, knowledge of both soil hydraulic and thermal properties and how they change in space and time is needed. Knowledge obtained from pore scale to macroscopic scale studies can help us to better understand these systems and contribute to the state of knowledge which can then be translated to engineering applications in the field (i.e. implementation of SBTES systems at the field scale). One important thermal property that varies with soil water content, effective thermal conductivity, is oftentimes included in numerical models through the use of empirical relationships and simplified mathematical formulations developed based on experimental data obtained at either small laboratory or field scales. These models assume that there is local thermodynamic equilibrium between the air and water phases for a representative elementary volume. However, this assumption may not always be valid at the pore scale, thus questioning the validity of current modeling approaches. The purpose of this work is to evaluate the validity of the local thermodynamic equilibrium assumption as related to the effective thermal conductivity at pore scale. A numerical model based on the coupled Cahn-Hilliard and heat transfer equation was developed to solve for liquid flow and heat transfer through variably saturated porous media. In this model, the evolution of phases and the interfaces between phases are related to a functional form of the total free energy of the system. A unique solution for the system is obtained by solving the Navier-Stokes equation through free energy minimization. Preliminary results demonstrate that there is a correlation between soil temperature / degree of saturation and equivalent thermal conductivity / heat flux. Results also confirm the correlation between pressure differential magnitude and equilibrium time for multiphase flow to reach steady state conditions. Based on these results, the equivalent time for steady-state heat transfer is much larger than the equivalent time for steady-state multiphase flow for a given pressure differential. Moreover, the wetting phase flow and consequently heat transfer appear to be sensitive to contact angle and porosity of the domain.

Pore-level mechanics of foam generation and coalescence in the presence of oil.

PubMed

Almajid, Muhammad M; Kovscek, Anthony R

2016-07-01

The stability of foam in porous media is extremely important for realizing the advantages of foamed gas on gas mobility reduction. Foam texture (i.e., bubbles per volume of gas) achieved is dictated by foam generation and coalescence processes occurring at the pore-level. For foam injection to be widely applied during gas injection projects, we need to understand these pore-scale events that lead to foam stability/instability so that they are modeled accurately. Foam flow has been studied for decades, but most efforts focused on studying foam generation and coalescence in the absence of oil. Here, the extensive existing literature is reviewed and analyzed to identify open questions. Then, we use etched-silicon micromodels to observe foam generation and coalescence processes at the pore-level. Special emphasis is placed on foam coalescence in the presence of oil. For the first time, lamella pinch-off as described by Myers and Radke [40] is observed in porous media and documented. Additionally, a new mechanism coined "hindered generation" is found. Hindered generation refers to the role oil plays in preventing the successful formation of a lamella following snap-off near a pore throat. Copyright © 2015 Elsevier B.V. All rights reserved.

Investigation of the Klinkenberg effect in a micro/nanoporous medium by direct simulation Monte Carlo method

NASA Astrophysics Data System (ADS)

Yang, Guang; Weigand, Bernhard

2018-04-01

The pressure-driven gas transport characteristics through a porous medium consisting of arrays of discrete elements is investigated by using the direct simulation Monte Carlo (DSMC) method. Different porous structures are considered, accounting for both two- and three-dimensional arrangements of basic microscale and nanoscale elements. The pore scale flow patterns in the porous medium are obtained, and the Knudsen diffusion in the pores is studied in detail for slip and transition flow regimes. A new effective pore size of the porous medium is defined, which is a function of the porosity, the tortuosity, the contraction factor, and the intrinsic permeability of the porous medium. It is found that the Klinkenberg effect in different porous structures can be fully described by the Knudsen number characterized by the effective pore size. The accuracies of some widely used Klinkenberg correlations are evaluated by the present DSMC results. It is also found that the available correlations for apparent permeability, most of which are derived from simple pipe or channel flows, can still be applicative for more complex porous media flows, by using the effective pore size defined in this study.

Smooth DNA transport through a narrowed pore geometry.

PubMed

Carson, Spencer; Wilson, James; Aksimentiev, Aleksei; Wanunu, Meni

2014-11-18

Voltage-driven transport of double-stranded DNA through nanoscale pores holds much potential for applications in quantitative molecular biology and biotechnology, yet the microscopic details of translocation have proven to be challenging to decipher. Earlier experiments showed strong dependence of transport kinetics on pore size: fast regular transport in large pores (> 5 nm diameter), and slower yet heterogeneous transport time distributions in sub-5 nm pores, which imply a large positional uncertainty of the DNA in the pore as a function of the translocation time. In this work, we show that this anomalous transport is a result of DNA self-interaction, a phenomenon that is strictly pore-diameter dependent. We identify a regime in which DNA transport is regular, producing narrow and well-behaved dwell-time distributions that fit a simple drift-diffusion theory. Furthermore, a systematic study of the dependence of dwell time on DNA length reveals a single power-law scaling of 1.37 in the range of 35-20,000 bp. We highlight the resolution of our nanopore device by discriminating via single pulses 100 and 500 bp fragments in a mixture with >98% accuracy. When coupled to an appropriate sequence labeling method, our observation of smooth DNA translocation can pave the way for high-resolution DNA mapping and sizing applications in genomics.

Oncogenic Mutations Differentially Affect Bax Monomer, Dimer, and Oligomeric Pore Formation in the Membrane.

PubMed

Zhang, Mingzhen; Zheng, Jie; Nussinov, Ruth; Ma, Buyong

2016-09-15

Dysfunction of Bax, a pro-apoptotic regulator of cellular metabolism is implicated in neurodegenerative diseases and cancer. We have constructed the first atomistic models of the Bax oligomeric pore consisting with experimental residue-residue distances. The models are stable, capturing well double electron-electron resonance (DEER) spectroscopy measurements and provide structural details in line with the DEER data. Comparison with the latest experimental results revealed that our models agree well with both Bax and Bak pores, pointed to a converged structural arrangement for Bax and Bak pore formation. Using multi-scale molecular dynamics simulations, we probed mutational effects on Bax transformation from monomer → dimer → membrane pore formation at atomic resolution. We observe that two cancer-related mutations, G40E and S118I, allosterically destabilize the monomer and stabilize an off-pathway swapped dimer, preventing productive pore formation. This observation suggests a mechanism whereby the mutations may work mainly by over-stabilizing the monomer → dimer transformation toward an unproductive off-pathway swapped-dimer state. Our observations point to misfolded Bax states, shedding light on the molecular mechanism of Bax mutation-elicited cancer. Most importantly, the structure of the Bax pore facilitates future study of releases cytochrome C in atomic detail.

Oncogenic Mutations Differentially Affect Bax Monomer, Dimer, and Oligomeric Pore Formation in the Membrane

NASA Astrophysics Data System (ADS)

Zhang, Mingzhen; Zheng, Jie; Nussinov, Ruth; Ma, Buyong

2016-09-01

Dysfunction of Bax, a pro-apoptotic regulator of cellular metabolism is implicated in neurodegenerative diseases and cancer. We have constructed the first atomistic models of the Bax oligomeric pore consisting with experimental residue-residue distances. The models are stable, capturing well double electron-electron resonance (DEER) spectroscopy measurements and provide structural details in line with the DEER data. Comparison with the latest experimental results revealed that our models agree well with both Bax and Bak pores, pointed to a converged structural arrangement for Bax and Bak pore formation. Using multi-scale molecular dynamics simulations, we probed mutational effects on Bax transformation from monomer → dimer → membrane pore formation at atomic resolution. We observe that two cancer-related mutations, G40E and S118I, allosterically destabilize the monomer and stabilize an off-pathway swapped dimer, preventing productive pore formation. This observation suggests a mechanism whereby the mutations may work mainly by over-stabilizing the monomer → dimer transformation toward an unproductive off-pathway swapped-dimer state. Our observations point to misfolded Bax states, shedding light on the molecular mechanism of Bax mutation-elicited cancer. Most importantly, the structure of the Bax pore facilitates future study of releases cytochrome C in atomic detail.

Big and small: menisci in soil pores affect water pressures, dynamics of groundwater levels, and catchment-scale average matric potentials

NASA Astrophysics Data System (ADS)

de Rooij, G. H.

2010-09-01

Soil water is confined behind the menisci of its water-air interface. Catchment-scale fluxes (groundwater recharge, evaporation, transpiration, precipitation, etc.) affect the matric potential, and thereby the interface curvature and the configuration of the phases. In turn, these affect the fluxes (except precipitation), creating feedbacks between pore-scale and catchment-scale processes. Tracking pore-scale processes beyond the Darcy scale is not feasible. Instead, for a simplified system based on the classical Darcy's Law and Laplace-Young Law we i) clarify how menisci transfer pressure from the atmosphere to the soil water, ii) examine large-scale phenomena arising from pore-scale processes, and iii) analyze the relationship between average meniscus curvature and average matric potential. In stagnant water, changing the gravitational potential or the curvature of the air-water interface changes the pressure throughout the water. Adding small amounts of water can thus profoundly affect water pressures in a much larger volume. The pressure-regulating effect of the interface curvature showcases the meniscus as a pressure port that transfers the atmospheric pressure to the water with an offset directly proportional to its curvature. This property causes an extremely rapid rise of phreatic levels in soils once the capillary fringe extends to the soil surface and the menisci flatten. For large bodies of subsurface water, the curvature and vertical position of any meniscus quantify the uniform hydraulic potential under hydrostatic equilibrium. During unit-gradient flow, the matric potential corresponding to the mean curvature of the menisci should provide a good approximation of the intrinsic phase average of the matric potential.

Estimating dynamic permeability in fractal pore network saturated by Maxwellian fluid

NASA Astrophysics Data System (ADS)

Sun, W.

2017-12-01

The frequency dependent flow of fluid in porous media is an important issue in geophysical prospecting. Oscillating flow in pipe leads to frequency dependent dynamic permeability and has been studied in pore network containing Newtonian fluid. But there is little work on oscillating complex fluid in pipe network, especially in irregular network. Here we formulated frequency dependent permeability for Maxwellian fluid and estimated the permeability in three-dimensional fractal network model. We consider an infinitely long cylindrical pipe with rigid solid wall. The pipe is filled with Maxwellian fluids. Based on the mass conservation equation, the equilibrium equation of force and Maxwell constitutive relationship, we formulated the flux by integration of axial velocity component over the pipe's cross section. Then we extend single pipe formulation to a 3D irregular network. Flux balance condition yields a set of linear equations whose unknowns are the fluid pressure at each node. By evaluating the total flow flux through the network, the dynamic permeability can be calculated.We investigated the dynamic permeability of brine and CPyCl/NaSal in a 3D porous sample with a cubic side length 1 cm. The pore network is created by a Voronoi cell filling method. The porosity, i.e., volume ratio between pore/pipe network and the overall cubic, is set as 0.1. The irregular pore network has a fractal structure. The dimension d of the pore network is defined by the relation between node number M within a sphere and the radius r of the sphere,M=rd.The results show that both brine and Maxwellian fluid's permeability maintain a stable value at low frequency, then decreases with fluctuating peaks. The dynamic permeability in pore networks saturated by Maxwellian fluid (CPyCl/NaSal (60 mM)) show larger peaks during the decline process at high frequency, which represents the typical resonance behavior. Dynamic permeability shows clear dependence on the dimension of the fractal network. Small-scale network has higher dimension than large-scale networks. The reason is that in larger networks pore and inter-pore connections are so dense that the probability P(r) to have a neighboring pore at distance r decays faster. The proposed model may be used to explain velocity dispersion in unconventional reservoir rocks observed in laboratory.

Pore-scale simulations of concentration tails in heterogeneous porous media

NASA Astrophysics Data System (ADS)

Di Palma, Paolo Roberto; Parmigiani, Andrea; Huber, Christian; Guyennon, Nicolas; Viotti, Paolo

2017-10-01

The retention of contaminants in the finest and less-conductive regions of natural aquifer is known to strongly affect the decontamination of polluted aquifers. In fact, contaminant transfer from low to high mobility regions at the back end of a contaminant plume (i.e. back diffusion) is responsible for the long-term release of contaminants during remediation operation. In this paper, we perform pore-scale calculations for the transport of contaminant through heterogeneous porous media composed of low and high mobility regions with two objectives: (i) study the effect of permeability contrast and solute transport conditions on the exchange of solutes between mobile and immobile regions and (ii) estimate the mass of contaminants sequestered in low mobility regions based on concentration breakthrough curves.

Upscaling soil saturated hydraulic conductivity from pore throat characteristics

NASA Astrophysics Data System (ADS)

Ghanbarian, Behzad; Hunt, Allen G.; Skaggs, Todd H.; Jarvis, Nicholas

2017-06-01

Upscaling and/or estimating saturated hydraulic conductivity Ksat at the core scale from microscopic/macroscopic soil characteristics has been actively under investigation in the hydrology and soil physics communities for several decades. Numerous models have been developed based on different approaches, such as the bundle of capillary tubes model, pedotransfer functions, etc. In this study, we apply concepts from critical path analysis, an upscaling technique first developed in the physics literature, to estimate saturated hydraulic conductivity at the core scale from microscopic pore throat characteristics reflected in capillary pressure data. With this new model, we find Ksat estimations to be within a factor of 3 of the average measured saturated hydraulic conductivities reported by Rawls et al. (1982) for the eleven USDA soil texture classes.

Rapid fabrication of self-ordered porous alumina with 10-/sub-10-nm-scale nanostructures by selenic acid anodizing

PubMed Central

Nishinaga, Osamu; Kikuchi, Tatsuya; Natsui, Shungo; Suzuki, Ryosuke O.

2013-01-01

Anodic porous alumina has been widely investigated and used as a nanostructure template in various nanoapplications. The porous structure consists of numerous hexagonal cells perpendicular to the aluminum substrate and each cell has several tens or hundreds of nanoscale pores at its center. Because the nanomorphology of anodic porous alumina is limited by the electrolyte during anodizing, the discovery of additional electrolytes would expand the applicability of porous alumina. In this study, we report a new self-ordered nanoporous alumina formed by selenic acid (H2SeO4) anodizing. By optimizing the anodizing conditions, anodic alumina possessing 10-nm-scale pores was rapidly assembled (within 1 h) during selenic acid anodizing without any special electrochemical equipment. Novel sub-10-nm-scale spacing can also be achieved by selenic acid anodizing and metal sputter deposition. Our new nanoporous alumina can be used as a nanotemplate for various nanostructures in 10-/sub-10-nm-scale manufacturing. PMID:24067318

Polymer translocation in solid-state nanopores: Dependence on hydrodynamic interactions and polymer configuration

NASA Astrophysics Data System (ADS)

Edmonds, Christopher M.; Hesketh, Peter J.; Nair, Sankar

2013-11-01

We present a Brownian dynamics investigation of 3-D Rouse and Zimm polymer translocation through solid-state nanopores. We obtain different scaling exponents α for both polymers using two initial configurations: minimum energy, and 'steady-state'. For forced translocation, Rouse polymers (no hydrodynamic interactions), shows a large dependence of α on initial configuration and voltage. Higher voltages result in crowding at the nanopore exit and reduced α. When the radius of gyration is in equilibrium at the beginning and end of translocation, α = 1 + υ where υ is the Flory exponent. For Zimm polymers (including hydrodynamic interactions), crowding is reduced and α = 2υ. Increased pore diameter does not affect α at moderate voltages that reduce diffusion effects. For unforced translocation using narrow pores, both polymers give α = 1 + 2υ. Due to increased polymer-pore interactions in the narrow pore, hydrodynamic drag effects are reduced, resulting in identical scaling.

Bio-inspired Murray materials for mass transfer and activity

NASA Astrophysics Data System (ADS)

Zheng, Xianfeng; Shen, Guofang; Wang, Chao; Li, Yu; Dunphy, Darren; Hasan, Tawfique; Brinker, C. Jeffrey; Su, Bao-Lian

2017-04-01

Both plants and animals possess analogous tissues containing hierarchical networks of pores, with pore size ratios that have evolved to maximize mass transport and rates of reactions. The underlying physical principles of this optimized hierarchical design are embodied in Murray's law. However, we are yet to realize the benefit of mimicking nature's Murray networks in synthetic materials due to the challenges in fabricating vascularized structures. Here we emulate optimum natural systems following Murray's law using a bottom-up approach. Such bio-inspired materials, whose pore sizes decrease across multiple scales and finally terminate in size-invariant units like plant stems, leaf veins and vascular and respiratory systems provide hierarchical branching and precise diameter ratios for connecting multi-scale pores from macro to micro levels. Our Murray material mimics enable highly enhanced mass exchange and transfer in liquid-solid, gas-solid and electrochemical reactions and exhibit enhanced performance in photocatalysis, gas sensing and as Li-ion battery electrodes.

Development of a New Analog Test System Capable of Modeling Tectonic Deformation Incorporating the Effects of Pore Fluid Pressure

NASA Astrophysics Data System (ADS)

Zhang, M.; Nakajima, H.; Takeda, M.; Aung, T. T.

2005-12-01

Understanding and predicting the tectonic deformation within geologic strata has been a very important research subject in many fields such as structural geology and petroleum geology. In recent years, such research has also become a fundamental necessity for the assessment of active fault migration, site selection for geological disposal of radioactive nuclear waste and exploration for methane hydrate. Although analog modeling techniques have played an important role in the elucidation of the tectonic deformation mechanisms, traditional approaches have typically used dry materials and ignored the effects of pore fluid pressure. In order for analog models to properly depict the tectonic deformation of the targeted, large-prototype system within a small laboratory-scale configuration, physical properties of the models, including geometry, force, and time, must be correctly scaled. Model materials representing brittle rock behavior require an internal friction identical to the prototype rock and virtually zero cohesion. Granular materials such as sand, glass beads, or steel beads of dry condition have been preferably used for this reason in addition to their availability and ease of handling. Modeling protocols for dry granular materials have been well established but such model tests cannot account for the pore fluid effects. Although the concept of effective stress has long been recognized and the role of pore-fluid pressure in tectonic deformation processes is evident, there have been few analog model studies that consider the effects of pore fluid movement. Some new applications require a thorough understanding of the coupled deformation and fluid flow processes within the strata. Taking the field of waste management as an example, deep geological disposal of radioactive waste has been thought to be an appropriate methodology for the safe isolation of the wastes from the human environment until the toxicity of the wastes decays to non-hazardous levels. For the deep geological disposal concept, besides containing the wastes with engineering methods such as the glassification of the radioactive wastes, the geological formation itself is expected to serve as a natural barrier that retards migration of radionuclides. To evaluate the long-term safety of deep geological disposal, a better understanding of the fate and transport of radionuclides in a geologically heterogeneous environment is necessary. To meet such requirements, a new analog test sandbox model system was developed. This model system allows the pore fluid flows to be controlled during the model tests and permits the study of flow and transport phenomena in the deformed heterogeneous model. One- or two-dimensional fluid flow is controlled using a side-wall piston. Deformation processes can be observed through a transparent front panel, and pore fluid movement can be also visualized using a color tracer. In this study, the scaling requirements for analog modeling, including pore water pressure, are discussed based on the theory of dimensional analysis, supplemented by data from a series of laboratory shear tests, and a detailed description of the model system. Preliminary experimental results are presented.

Fabrication of scalable tissue engineering scaffolds with dual-pore microarchitecture by combining 3D printing and particle leaching.

PubMed

Mohanty, Soumyaranjan; Sanger, Kuldeep; Heiskanen, Arto; Trifol, Jon; Szabo, Peter; Dufva, Marin; Emnéus, Jenny; Wolff, Anders

2016-04-01

Limitations in controlling scaffold architecture using traditional fabrication techniques are a problem when constructing engineered tissues/organs. Recently, integration of two pore architectures to generate dual-pore scaffolds with tailored physical properties has attracted wide attention in tissue engineering community. Such scaffolds features primary structured pores which can efficiently enhance nutrient/oxygen supply to the surrounding, in combination with secondary random pores, which give high surface area for cell adhesion and proliferation. Here, we present a new technique to fabricate dual-pore scaffolds for various tissue engineering applications where 3D printing of poly(vinyl alcohol) (PVA) mould is combined with salt leaching process. In this technique the sacrificial PVA mould, determining the structured pore architecture, was filled with salt crystals to define the random pore regions of the scaffold. After crosslinking the casted polymer the combined PVA-salt mould was dissolved in water. The technique has advantages over previously reported ones, such as automated assembly of the sacrificial mould, and precise control over pore architecture/dimensions by 3D printing parameters. In this study, polydimethylsiloxane and biodegradable poly(ϵ-caprolactone) were used for fabrication. However, we show that this technique is also suitable for other biocompatible/biodegradable polymers. Various physical and mechanical properties of the dual-pore scaffolds were compared with control scaffolds with either only structured or only random pores, fabricated using previously reported methods. The fabricated dual-pore scaffolds supported high cell density, due to the random pores, in combination with uniform cell distribution throughout the scaffold, and higher cell proliferation and viability due to efficient nutrient/oxygen transport through the structured pores. In conclusion, the described fabrication technique is rapid, inexpensive, scalable, and compatible with different polymers, making it suitable for engineering various large scale organs/tissues. Copyright © 2015. Published by Elsevier B.V.

Application of method of volume averaging coupled with time resolved PIV to determine transport characteristics of turbulent flows in porous bed

NASA Astrophysics Data System (ADS)

Patil, Vishal; Liburdy, James

2012-11-01

Turbulent porous media flows are encountered in catalytic bed reactors and heat exchangers. Dispersion and mixing properties of these flows play an essential role in efficiency and performance. In an effort to understand these flows, pore scale time resolved PIV measurements in a refractive index matched porous bed were made. Pore Reynolds numbers, based on hydraulic diameter and pore average velocity, were varied from 400-4000. Jet-like flows and recirculation regions associated with large scale structures were found to exist. Coherent vortical structures which convect at approximately 0.8 times the pore average velocity were identified. These different flow regions exhibited different turbulent characteristics and hence contributed unequally to global transport properties of the bed. The heterogeneity present within a pore and also from pore to pore can be accounted for in estimating transport properties using the method of volume averaging. Eddy viscosity maps and mean velocity field maps, both obtained from PIV measurements, along with the method of volume averaging were used to predict the dispersion tensor versus Reynolds number. Asymptotic values of dispersion compare well to existing correlations. The role of molecular diffusion was explored by varying the Schmidt number and molecular diffusion was found to play an important role in tracer transport, especially in recirculation regions. Funding by NSF grant 0933857, Particulate and Multiphase Processing.

Characterizing TPS Microstructure: A Review of Some techniques

NASA Technical Reports Server (NTRS)

Gasch, Matthew; Stackpole, Mairead; Agrawal, Parul; Chavez-Garcie, Jose

2011-01-01

I. When seeking to understand ablator microstructure and morphology there are several useful techniques A. SEM 1) Visual characteriza3on at various length scales. 2) Chemical mapping by backscatter or x-ray highlights areas of interest. 3) Combined with other techniques (density, weight change, chemical analysis) SEM is a powerful tool to aid in explaining thermo/structural data. B. ASAP. 1) Chemical characteriza3on at various length scales. 2) Chemical mapping of pore structure by gas adsorption. 3) Provides a map of pore size vs. pore volume. 4) Provided surface area of exposed TPS. II. Both methods help characterize and understand how ablators react with other chemical species and provides insight into how they oxidize.

Slip-flow in complex porous media as determined by a multi-relaxation-time lattice Boltzmann model

NASA Astrophysics Data System (ADS)

Landry, C. J.; Prodanovic, M.; Eichhubl, P.

2014-12-01

The pores and throats of shales and mudrocks are predominantly found within a range of 1-100 nm, within this size range the flow of gas at reservoir conditions will fall within the slip-flow and low transition-flow regime (0.001 < Kn < 0.5). Currently, the study of slip-flows is for the most part limited to simple tube and channel geometries, however, the geometry of mudrock pores is often sponge-like (organic matter) and/or platy (clays). Molecular dynamics (MD) simulations can be used to predict slip-flow in complex geometries, but due to prohibitive computational demand are generally limited to small volumes (one to several pores). Here we present a multi-relaxation-time lattice Boltzmann model (LBM) parameterized for slip-flow (Guo et al. 2008) and adapted here to complex geometries. LBMs are inherently parallelizable, such that flow in complex geometries of significant (near REV-scale) volumes can be readily simulated at a fraction of the computational cost of MD simulations. At the macroscopic-scale the LBM is parameterized with local effective viscosities at each node to capture the variance of the mean-free-path of gas molecules in a bounded system. The corrected mean-free-path for each lattice node is determined using the mean distance of the node to the pore-wall and Stop's correction for mean-free-paths in an infinite parallel-plate geometry. At the microscopic-scale, a combined bounce-back specular-reflection boundary condition is applied to the pore-wall nodes to capture Maxwellian-slip. The LBM simulation results are first validated in simple tube and channel geometries, where good agreement is found for Knudsen numbers below 0.1, and fair agreement is found for Knudsen numbers between 0.1 and 0.5. More complex geometries are then examined including triangular-ducts and ellipsoid-ducts, both with constant and tapering/expanding cross-sections, as well as a clay pore-network imaged from a hydrocarbon producing shale by sequential focused ion-beam scanning electron microscopy. These results are analyzed to determine grid-independent resolutions, and used to explore the relationship between effective permeability and Knudsen number in complex geometries.

Pore geometry effects on intrapore viscous to inertial flows and on effective hydraulic parameters

NASA Astrophysics Data System (ADS)

Chaudhary, Kuldeep; Cardenas, M. Bayani; Deng, Wen; Bennett, Philip C.

2013-02-01

In this article, the effects of different diverging-converging pore geometries were investigated, and the microscale fluid flow and effective hydraulic properties from these pores were compared with that of a pipe from viscous to inertial laminar flow regimes. The flow fields are obtained using computational fluid dynamics, and the comparative analysis is based on a new dimensionless hydraulic shape factor β, which is the "specific surface" scaled by the length of pores. Results from all diverging-converging pores show an inverse pattern in velocity and vorticity distributions relative to the pipe flow. The hydraulic conductivity K of all pores is dependent on and can be predicted from β with a power function with an exponent of 3/2. The differences in K are due to the differences in distribution of local friction drag on the pore walls. At Reynolds number (Re) ˜ 0 flows, viscous eddies are found to exist almost in all pores in different sizes, but not in the pipe. Eddies grow when Re → 1 and leads to the failure of Darcy's law. During non-Darcy or Forchheimer flows, the apparent hydraulic conductivity Ka decreases due to the growth of eddies, which constricts the bulk flow region. At Re > 1, the rate of decrease in Ka increases, and at Re >> 1, it decreases to where the change in Ka ≈ 0, and flows once again exhibits a Darcy-type relationship. The degree of nonlinearity during non-Darcy flow decreases for pores with increasing β. The nonlinear flow behavior becomes weaker as β increases to its maximum value in the pipe, which shows no nonlinearity in the flow; in essence, Darcy's law stays valid in the pipe at all laminar flow conditions. The diverging-converging geometry in pores plays a critical role in modifying the intrapore fluid flow, implying that this property should be incorporated in effective larger-scale models, e.g., pore-network models.

Structural characteristics of gels prepared from sonohydrolysis and conventional hydrolysis of TEOS: an emphasis on the mass fractal as determined from the pore size distribution

NASA Astrophysics Data System (ADS)

Vollet, D. R.; Torres, R. R.; Donatti, D. A.; Ibañez Ruiz, A.

2005-11-01

Silica gels were preparated from fixed proportion mixtures of tetraethoxysilane, water and hydrocloric acid, using either ultrasound stimulation (US) or conventional method (CO) in the hydrolysis step of the process. Wet gels were obtained with the same silica volume concentration and density. According to small-angle X-ray scattering, the structure of the wet gels can be described as mass fractal structures with mass fractal dimension D = 2.20 in a length scale = 7.9 nm, in the case of wet gels US, and D = 2.26 in a length scale = 6.9 nm, in the case of wet gels CO. The mass fractal characteristics of the wet gels US and CO account for the different structures evolved in the drying of the gels US and CO in the obtaining of xerogels and aerogels. The pore structure of the dried gels was studied by nitrogen adsorption as a function of the temperature. Aerogels (US and CO) present high porosity with pore size distribution (PSD) curves in the mesopore region while xerogels (US and CO) present minor porosity with PSD curves mainly in the micropore region. The dried gels US (aerogels and xerogels) generally present pore volume and specific surface area greater than the dried gels CO. The mass fractal structure of the aerogels has been studied from an approach based on the PSD curves exclusively.

Micro-PIV measurements of multiphase flow of water and liquid CO2 in 2-D heterogeneous porous micromodels

NASA Astrophysics Data System (ADS)

Li, Yaofa; Kazemifar, Farzan; Blois, Gianluca; Christensen, Kenneth T.

2017-07-01

We present an experimental study of pore-scale flow dynamics of liquid CO2 and water in a two-dimensional heterogeneous porous micromodel, inspired by the structure of a reservoir rock, at reservoir-relevant conditions (80 bar, 21°C). The entire process of CO2 infiltration into a water-saturated micromodel was captured using fluorescence microscopy and the micro-PIV method, which together reveal complex fluid displacement patterns and abrupt changes in velocity. The CO2 front migrated through the resident water in an intermittent manner, forming dendritic structures, termed fingers, in directions along, normal to, and even opposing the bulk pressure gradient. Such characteristics indicate the dominance of capillary fingering through the micromodel. Velocity burst events, termed Haines jumps, were also captured in the heterogeneous micromodel, during which the local Reynolds number was estimated to be ˜21 in the CO2 phase, exceeding the range of validity of Darcy's law. Furthermore, these drainage events were observed to be cooperative (i.e., across multiple pores simultaneously), with the zone of influence of such events extending beyond tens of pores, confirming, in a quantitative manner, that Haines jumps are nonlocal phenomena. After CO2 completely breaks through the porous section, shear-induced circulations caused by flowing CO2 were also observed, in agreement with previous studies using a homogeneous porous micromodel. To our knowledge, this study is the first quantitative measurement that incorporates both reservoir-relevant conditions and rock-inspired heterogeneity, and thus will be useful for pore-scale model development and validation.

Physics Applied to Oil and Gas Exploration

NASA Astrophysics Data System (ADS)

Schwartz, Larry

2002-03-01

Problems involving transport in porous media are of interest throughout the fields of petroleum exploration and environmental monitoring and remediation. The systems being studied can vary in size from centimeter scale rock or soil samples to kilometer scale reservoirs and aquifers. Clearly, the smaller the sample the more easily can the medium's structure and composition be characterized, and the better defined are the associated experimental and theoretical modeling problems. The study of transport in such geological systems is then similar to corresponding problems in the study of other heterogeneous systems such as polymer gels, catalytic beds and cementitious materials. The defining characteristic of porous media is that they are comprised of two percolating interconnected channels, the solid and pore networks. Transport processes of interest in such systems typically involve the flow of electrical current, viscous fluids or fine grained particles. A closely related phenomena, nuclear magnetic resonance (NMR), is controlled by diffusion in the pore network. Also of interest is the highly non-linear character of the stress-strain response of granular porous media. We will review the development of two and three dimensional model porous media, and will outline the calculation of their physical properties. We will also discuss the direct measurement of the pore structure by synchrotron X-ray microtomography.

Scale-Dependent Rates of Uranyl Surface Complexation Reaction in Sediments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Chongxuan; Shang, Jianying; Kerisit, Sebastien N.

Scale-dependency of uranyl[U(VI)] surface complexation rates was investigated in stirred flow-cell and column systems using a U(VI)-contaminated sediment from the US Department of Energy, Hanford site, WA. The experimental results were used to estimate the apparent rate of U(VI) surface complexation at the grain-scale and in porous media. Numerical simulations using molecular, pore-scale, and continuum models were performed to provide insights into and to estimate the rate constants of U(VI) surface complexation at the different scales. The results showed that the grain-scale rate constant of U(VI) surface complexation was over 3 to 10 orders of magnitude smaller, dependent on themore » temporal scale, than the rate constant calculated using the molecular simulations. The grain-scale rate was faster initially and slower with time, showing the temporal scale-dependency. The largest rate constant at the grain-scale decreased additional 2 orders of magnitude when the rate was scaled to the porous media in the column. The scaling effect from the grain-scale to the porous media became less important for the slower sorption sites. Pore-scale simulations revealed the importance of coupled mass transport and reactions in both intragranular and inter-granular domains, which caused both spatial and temporal dependence of U(VI) surface complexation rates in the sediment. Pore-scale simulations also revealed a new rate-limiting mechanism in the intragranular porous domains that the rate of coupled diffusion and surface complexation reaction was slower than either process alone. The results provided important implications for developing models to scale geochemical/biogeochemical reactions.« less

Poroelastic stress-triggering of the 2005 M8.7 Nias earthquake by the 2004 M9.2 Sumatra-Andaman earthquake

USGS Publications Warehouse

Hughes, K.L.H.; Masterlark, Timothy; Mooney, W.D.

2010-01-01

The M9.2 Sumatra-Andaman earthquake (SAE) occurred three months prior to the M8.7 Nias earthquake (NE). We propose that the NE was mechanically triggered by the SAE, and that poroelastic effects were a major component of this triggering. This study uses 3D finite element models (FEMs) of the Sumatra-Andaman subduction zone (SASZ) to predict the deformation, stress, and pore pressure fields of the SAE. The coseismic slip distribution for the SAE is calibrated to near-field GPS data using FEM-generated Green's Functions and linear inverse methods. The calibrated FEM is then used to predict the postseismic poroelastic contribution to stress-triggering along the rupture surface of the NE, which is adjacent to the southern margin of the SAE. The coseismic deformation of the SAE, combined with the rheologic configuration of the SASZ produces two transient fluid flow regimes having separate time constants. SAE coseismic pore pressures in the relatively shallow forearc and volcanic arc regions (within a few km depth) dissipate within one month after the SAE. However, pore pressures in the oceanic crust of the down-going slab persist several months after the SAE. Predictions suggest that the SAE initially induced MPa-scale negative pore pressure near the hypocenter of the NE. This pore pressure slowly recovered (increased) during the three-month interval separating the SAE and NE due to lateral migration of pore fluids, driven by coseismic pressure gradients, within the subducting oceanic crust. Because pore pressure is a fundamental component of Coulomb stress, the MPa-scale increase in pore pressure significantly decreased stability of the NE fault during the three-month interval after the SAE and prior to rupture of the NE. A complete analysis of stress-triggering due to the SAE must include a poroelastic component. Failure to include poroelastic mechanics will lead to an incomplete model that cannot account for the time interval between the SAE and NE. Our transient poroelastic model explains both the spatial and temporal characteristics of triggering of the NE by the SAE. ?? 2010 Elsevier B.V.

Pore-scale analysis of the minimum liquid film thickness around elongated bubbles in confined gas-liquid flows

NASA Astrophysics Data System (ADS)

Magnini, M.; Beisel, A. M.; Ferrari, A.; Thome, J. R.

2017-11-01

The fluid mechanics of elongated bubbles in confined gas-liquid flows in micro-geometries is important in pore-scale flow processes for enhanced oil recovery and mobilization of colloids in unsaturated soil. The efficiency of such processes is traditionally related to the thickness of the liquid film trapped between the elongated bubble and the pore's wall, which is assumed constant. However, the surface of long bubbles presents undulations in the vicinity of the rear meniscus, which may significantly decrease the local thickness of the liquid film, thus impacting the process of interest. This study presents a systematic analysis of these undulations and the minimum film thickness induced in the range Ca = 0.001- 0.5 and Re = 0.1- 2000 . Pore-scale Computational Fluid Dynamics (CFD) simulations are performed with a self-improved version of the opensource solver ESI OpenFOAM which is based on a Volume of Fluid method to track the gas-liquid interface. A lubrication model based on the extension of the classical axisymmetric Bretherton theory is utilized to better understand the CFD results. The profiles of the rear meniscus of the bubble obtained with the lubrication model agree fairly well with those extracted from the CFD simulations. This study shows that the Weber number of the flow, We = Ca Re , is the parameter that best describes the dynamics of the interfacial waves. When We < 0.1, a single wave crest is observed and the minimum film thickness tends to an asymptotic value, which depends on the capillary number, as We → 0. Undulations dampen as the capillary number increases and disappear completely when Ca = 0.5 . When We > 0.1, a larger number of wave crests becomes evident on the surface of the rear meniscus of the bubble. The liquid film thickness at the crests of the undulations thins considerably as the Reynolds number is increased, down to less than 60% of the value measured in the flat film region. This may significantly influence important environmental processes, such as the detachment and mobilization of micron-sized pollutants and pathogenic micro-organisms adhering at the pore's wall in unsaturated soil.

Pore-scale dynamics of salt transport and distribution in drying porous media

NASA Astrophysics Data System (ADS)

Shokri, Nima

2014-01-01

Understanding the physics of water evaporation from saline porous media is important in many natural and engineering applications such as durability of building materials and preservation of monuments, water quality, and mineral-fluid interactions. We applied synchrotron x-ray micro-tomography to investigate the pore-scale dynamics of dissolved salt distribution in a three dimensional drying saline porous media using a cylindrical plastic column (15 mm in height and 8 mm in diameter) packed with sand particles saturated with CaI2 solution (5% concentration by mass) with a spatial and temporal resolution of 12 μm and 30 min, respectively. Every time the drying sand column was set to be imaged, two different images were recorded using distinct synchrotron x-rays energies immediately above and below the K-edge value of Iodine. Taking the difference between pixel gray values enabled us to delineate the spatial and temporal distribution of CaI2 concentration at pore scale. Results indicate that during early stages of evaporation, air preferentially invades large pores at the surface while finer pores remain saturated and connected to the wet zone at bottom via capillary-induced liquid flow acting as evaporating spots. Consequently, the salt concentration increases preferentially in finer pores where evaporation occurs. Higher salt concentration was observed close to the evaporating surface indicating a convection-driven process. The obtained salt profiles were used to evaluate the numerical solution of the convection-diffusion equation (CDE). Results show that the macro-scale CDE could capture the overall trend of the measured salt profiles but fail to produce the exact slope of the profiles. Our results shed new insight on the physics of salt transport and its complex dynamics in drying porous media and establish synchrotron x-ray tomography as an effective tool to investigate the dynamics of salt transport in porous media at high spatial and temporal resolution.

Pore-scale dynamics of salt transport and distribution in drying porous media

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shokri, Nima, E-mail: nima.shokri@manchester.ac.uk

2014-01-15

Understanding the physics of water evaporation from saline porous media is important in many natural and engineering applications such as durability of building materials and preservation of monuments, water quality, and mineral-fluid interactions. We applied synchrotron x-ray micro-tomography to investigate the pore-scale dynamics of dissolved salt distribution in a three dimensional drying saline porous media using a cylindrical plastic column (15 mm in height and 8 mm in diameter) packed with sand particles saturated with CaI{sub 2} solution (5% concentration by mass) with a spatial and temporal resolution of 12 μm and 30 min, respectively. Every time the drying sandmore » column was set to be imaged, two different images were recorded using distinct synchrotron x-rays energies immediately above and below the K-edge value of Iodine. Taking the difference between pixel gray values enabled us to delineate the spatial and temporal distribution of CaI{sub 2} concentration at pore scale. Results indicate that during early stages of evaporation, air preferentially invades large pores at the surface while finer pores remain saturated and connected to the wet zone at bottom via capillary-induced liquid flow acting as evaporating spots. Consequently, the salt concentration increases preferentially in finer pores where evaporation occurs. Higher salt concentration was observed close to the evaporating surface indicating a convection-driven process. The obtained salt profiles were used to evaluate the numerical solution of the convection-diffusion equation (CDE). Results show that the macro-scale CDE could capture the overall trend of the measured salt profiles but fail to produce the exact slope of the profiles. Our results shed new insight on the physics of salt transport and its complex dynamics in drying porous media and establish synchrotron x-ray tomography as an effective tool to investigate the dynamics of salt transport in porous media at high spatial and temporal resolution.« less

Coupling root architecture and pore network modeling - an attempt towards better understanding root-soil interactions

NASA Astrophysics Data System (ADS)

Leitner, Daniel; Bodner, Gernot; Raoof, Amir

2013-04-01

Understanding root-soil interactions is of high importance for environmental and agricultural management. Root uptake is an essential component in water and solute transport modeling. The amount of groundwater recharge and solute leaching significantly depends on the demand based plant extraction via its root system. Plant uptake however not only responds to the potential demand, but in most situations is limited by supply form the soil. The ability of the plant to access water and solutes in the soil is governed mainly by root distribution. Particularly under conditions of heterogeneous distribution of water and solutes in the soil, it is essential to capture the interaction between soil and roots. Root architecture models allow studying plant uptake from soil by describing growth and branching of root axes in the soil. Currently root architecture models are able to respond dynamically to water and nutrient distribution in the soil by directed growth (tropism), modified branching and enhanced exudation. The porous soil medium as rooting environment in these models is generally described by classical macroscopic water retention and sorption models, average over the pore scale. In our opinion this simplified description of the root growth medium implies several shortcomings for better understanding root-soil interactions: (i) It is well known that roots grow preferentially in preexisting pores, particularly in more rigid/dry soil. Thus the pore network contributes to the architectural form of the root system; (ii) roots themselves can influence the pore network by creating preferential flow paths (biopores) which are an essential element of structural porosity with strong impact on transport processes; (iii) plant uptake depend on both the spatial location of water/solutes in the pore network as well as the spatial distribution of roots. We therefore consider that for advancing our understanding in root-soil interactions, we need not only to extend our root models, but also improve the description of the rooting environment. Until now there have been no attempts to couple root architecture and pore network models. In our work we present a first attempt to join both types of models using the root architecture model of Leitner et al., (2010) and a pore network model presented by Raoof et al. (2010). The two main objectives of coupling both models are: (i) Representing the effect of root induced biopores on flow and transport processes: For this purpose a fixed root architecture created by the root model is superimposed as a secondary root induced pore network to the primary soil network, thus influencing the final pore topology in the network generation. (ii) Representing the influence of pre-existing pores on root branching: Using a given network of (rigid) pores, the root architecture model allocates its root axes into these preexisting pores as preferential growth paths with thereby shape the final root architecture. The main objective of our study is to reveal the potential of using a pore scale description of the plant growth medium for an improved representation of interaction processes at the interface of root and soil. References Raoof, A., Hassanizadeh, S.M. 2010. A New Method for Generating Pore-Network Models. Transp. Porous Med. 81, 391-407. Leitner, D, Klepsch, S., Bodner, G., Schnepf, S. 2010. A dynamic root system growth model based on L-Systems. Tropisms and coupling to nutrient uptake from soil. Plant Soil 332, 177-192.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li Wei; Faculty of Science, Kunming University of Science and Technology, Kunming 650093; Peng Jinhui

Experiments to prepare activated carbon by microwave heating indicated that microwave energy can decrease reaction temperature, save the energy and shorten processing time remarkably compared to conventional heating, owing to its internal and volumetric heating effects. The above results were based on the laboratory-scale experiments. It is desirable to develop a pilot-scale microwave heating equipment and investigate the parameters with the aim of technological industrialization. In the present study, the components and features of the self-invented equipment were introduced. The temperature rise curves of the chars were obtained. Iodine numbers of the activated carbons all exceed the state standard ofmore » China under the following conditions: 25 kg/h charging rate, 0.42 rev/min turning rate of ceramic tube, flow rate of steam at pressure of 0.01 MPa and 40 kW microwave heating power after 60 kW pre-activation for 30 min. Pore structure of the sample obtained at a time point of 46 h, which contained BET surface area, and pore size distributions of micropores and total pores, was tested by nitrogen adsorption at 77 K.« less

EFFECTS OF PORE STRUCTURE CHANGE AND MULTI-SCALE HETEROGENEITY ON CONTAMINANT TRANSPORT AND REACTION RATE UPSCALING

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lindquist, W. Brent; Jones, Keith W.; Um, Wooyong

2013-02-15

This project addressed the scaling of geochemical reactions to core and field scales, and the interrelationship between reaction rates and flow in porous media. We targeted reactive transport problems relevant to the Hanford site - specifically the reaction of highly caustic, radioactive waste solutions with subsurface sediments, and the immobilization of 90Sr and 129I through mineral incorporation and passive flow blockage, respectively. We addressed the correlation of results for pore-scale fluid-soil interaction with field-scale fluid flow, with the specific goals of (i) predicting attenuation of radionuclide concentration; (ii) estimating changes in flow rates through changes of soil permeabilities; and (iii)more » estimating effective reaction rates. In supplemental work, we also simulated reactive transport systems relevant to geologic carbon sequestration. As a whole, this research generated a better understanding of reactive transport in porous media, and resulted in more accurate methods for reaction rate upscaling and improved prediction of permeability evolution. These scientific advancements will ultimately lead to better tools for management and remediation of DOE’s legacy waste problems. We established three key issues of reactive flow upscaling, and organized this project in three corresponding thrust areas. 1) Reactive flow experiments. The combination of mineral dissolution and precipitation alters pore network structure and the subsequent flow velocities, thereby creating a complex interaction between reaction and transport. To examine this phenomenon, we conducted controlled laboratory experimentation using reactive flow-through columns. Results and Key Findings: Four reactive column experiments (S1, S3, S4, S5) have been completed in which simulated tank waste leachage (STWL) was reacted with pure quartz sand, with and without Aluminum. The STWL is a caustic solution that dissolves quartz. Because Al is a necessary element in the formation of secondary mineral precipitates (cancrinite), conducting experiments under conditions with and without Al allowed us to experimentally separate the conditions that lead to quartz dissolution from the conditions that lead to quartz dissolution plus cancrinite precipitation. Consistent with our expectations, in the experiments without Al, there was a substantial reduction in volume of the solid matrix. With Al there was a net increase in the volume of the solid matrix. The rate and extent of reaction was found to increase with temperature. These results demonstrate a successful effort to identify conditions that lead to increases and conditions that lead to decreases in solid matrix volume due to reactions of caustic tank wastes with quartz sands. In addition, we have begun to work with slightly larger, intermediate-scale columns packed with Hanford natural sediments and quartz. Similar dissolution and precipitation were observed in these colums. The measurements are being interpreted with reactive transport modeling using STOMP; preliminary observations are reported here. 2) Multi-Scale Imaging and Analysis. Mineral dissolution and precipitation rates within a porous medium will be different in different pores due to natural heterogeneity and the heterogeneity that is created from the reactions themselves. We used a combination of X-ray computed microtomography, backscattered electron and energy dispersive X-ray spectroscopy combined with computational image analysis to quantify pore structure, mineral distribution, structure changes and fluid-air and fluid-grain interfaces. Results and Key Findings: Three of the columns from the reactive flow experiments at PNNL (S1, S3, S4) were imaged using 3D X-ray computed microtomography (XCMT) at BNL and analyzed using 3DMA-rock at SUNY Stony Brook. The imaging results support the mass balance findings reported by Dr. Um’s group, regarding the substantial dissolution of quartz in column S1. An important observation is that of grain movement accompanying dissolution in the unconsolidated media. The resultant movement changes the anticipated findings for pore and throat size distributions. For column S3, with cancrinite precipitation accompanying quartz dissolution, the precitiation halts much of the grain movement and more systematic distributions are obtained. Column S4, which was sealed with caustic solution acted as a control sample to study reactive effects during periods when columns S1 and S3 were sealed between flow experiments. No significant changes are observed in S4 with time. At Princeton, the imaging and analysis work focused on the effects of mineral precipitation and advancing our understanding of the impacts of these reactions on reactive transport in subsurface sediments. These findings are described in detail below, and have been published in L.E. Crandell, C.A. Peters, W. Um, K.W. Jones, W.B. Lindquist, 2012. “Changes in the pore network structure of Hanford sediment after reaction with caustic tank wastes.” Journal of Contaminant Hydrology 131 (2012) 89–99. 3) Multi-Scale Modeling and Up-Scaling. Using an array of modeling approaches, we examined pore-scale variations in physical and mineralogical properties, flow velocities, and (for unsaturated conditions) wetting fluid/grain surface areas, and permeability evolution. Results and Key Findings: To predict the column permeability and estimate the impact of mineral precipitation, pore network models were informed using the pore and throat-size distributions from the imaging analyses. As a comparison, supplemental analyses were performed on Viking sandstone specimens from the Alberta sedimentary basin. In another part of this study we sought to understand how carbonate rocks in contact with CO2-rich brines change due to the precipitation or dissolution of fast-reacting minerals such as calcite and dolomite. Using a newly developed reactive-transport pore-network model we were able to identify the conditions that lead to significant permeability changes. These findings are presented below and are compiled in a publication that is under review: J.P. Nogues, J.P. Fitts, M.A. Celia, C.A. Peters. “Permeability evolution due to dissolution and precipitation of carbonates using reactive transport modeling in pore networks”, Submitted: Water Resources Research, 2013.« less

Focused ion beam assisted three-dimensional rock imaging at submicron scale

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tomutsa, Liviu; Radmilovic, Velimir

2003-05-09

Computation of effective flow properties of fluids in porous media based on three dimensional (3D) pore structure information has become more successful in the last few years, due to both improvements in the input data and the network models. Computed X-ray microtomography has been successful in 3D pore imaging at micron scale, which is adequate for many sandstones. For other rocks of economic interest, such as chalk and diatomite, submicron resolution is needed in order to resolve the 3D-pore structure. To achieve submicron resolution, a new method of sample serial sectioning and imaging using Focused Ion Beam (FIB) technology hasmore » been developed and 3D pore images of the pore system for diatomite and chalk have been obtained. FIB was used in the milling of layers as wide as 50 micrometers and as thin as 100 nanometers by sputtering of atoms from the sample surface. The focused ion beam, consisting of gallium ions (Ga+) accelerated by potentials of up to 30 kV and currents up to 20,000 pA, yields very clean, flat surfaces in which the pore-grain boundaries appear in high contrast. No distortion of the pore boundaries due to the ion milling is apparent. After each milling step, as a new surface is exposed, an image of the surface is generated. Using secondary electrons or ions, resolutions as high as 10 nm can be obtained. Afterwards, the series of 2D images can be stacked in the computer and, using appropriate interpolation and surface rendering algorithms, the 3D pore structure is reconstructed.« less

A Theoretical Analysis of the Interaction Between Pores and Inclusions During the Continuous Casting of Steel

NASA Astrophysics Data System (ADS)

Nick, Arash Safavi; Vynnycky, Michael; Fredriksson, Hasse

2016-06-01

A mathematical model is derived to predict the trajectories of pores and inclusions that are nucleated in the interdendritic region during the continuous casting of steel. Using basic fluid mechanics and heat transfer, scaling analysis, and asymptotic methods, the model accounts for the possible lateral drift of the pores as a result of the dependence of the surface tension on temperature and sulfur concentration. Moreover, the soluto-thermocapillary drift of such pores prior to final solidification, coupled to the fact that any inclusions present can only have a vertical trajectory, can help interpret recent experimental observations of pore-inclusion clusters in solidified steel castings.

Non-perturbative Quantification of Ionic Charge Transfer through Nm-Scale Protein Pores Using Graphene Microelectrodes

NASA Astrophysics Data System (ADS)

Ping, Jinglei; Johnson, A. T. Charlie; A. T. Charlie Johnson Team

Conventional electrical methods for detecting charge transfer through protein pores perturb the electrostatic condition of the solution and chemical reactivity of the pore, and are not suitable to be used for complex biofluids. We developed a non-perturbative methodology ( fW input power) for quantifying trans-pore electrical current and detecting the pore status (i.e., open vs. closes) via graphene microelectrodes. Ferritin was used as a model protein featuring a large interior compartment, well-separated from the exterior solution with discrete pores as charge commuting channels. The charge flowing through the ferritin pores transfers into the graphene microelectrode and is recorded by an electrometer. In this example, our methodology enables the quantification of an inorganic nanoparticle-protein nanopore interaction in complex biofluids. The authors acknowledge the support from the Defense Advanced Research Projects Agency (DARPA) and the U.S. Army Research Office under Grant Number W911NF1010093.

A detailed study of CO 2-brine capillary trapping mechanisms as applied to geologic carbon storage. Final Report

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wildenschild, Dorthe

2017-04-06

The proposed research focuses on improved fundamental understanding of the efficiency of physical trapping mechanisms, and as such will provide the basis for subsequent upscaling efforts. The overarching hypothesis of the proposed research is that capillary pressure plays a significant role in capillary trapping of CO 2, especially during the water imbibition stage of the sequestration process. We posit that the relevant physics of the sequestration process is more complex than is currently captured in relative permeability models, which are often based on so-called trapping models to represent relative permeability hysteresis. Our 4 main questions, guiding the 4 main tasksmore » of the proposed research, are as follows: (1) What is the morphology of capillary trapped CO 2 at the pore scale as a function of temperature, pressure, brine concentration, interfacial tension, and pore-space morphology under injection and subsequent imbibition? (2) Is it possible to describe the capillary trapping process using formation-dependent, but otherwise unique continuum-scale functions in permeability-capillary pressure, interfacial area and saturation space, rather than hysteretic functions in permeability-saturation or capillary pressure-saturation space? (3) How do continuum-scale relationships between kr-Pc-S-Anw developed based on pore-scale observations compare with traditional models incorporating relative permeability hysteresis (such as Land’s and other models,) and with observations at the core (5-10cm) scale? (4) How can trapped CO 2 volume be optimized via engineered injection and sweep strategies, and as a function of formation type (incl. heterogeneity)?« less

Investigating textural controls on Archie's porosity exponent using process-based, pore-scale modelling

NASA Astrophysics Data System (ADS)

Niu, Q.; Zhang, C.

2017-12-01

Archie's law is an important empirical relationship linking the electrical resistivity of geological materials to their porosity. It has been found experimentally that the porosity exponent m in Archie's law in sedimentary rocks might be related to the degree of cementation, and therefore m is termed as "cementation factor" in most literatures. Despite it has been known for many years, there is lack of well-accepted physical interpretations of the porosity exponent. Some theoretical and experimental evidences have also shown that m may be controlled by the particle and/or pore shape. In this study, we conduct a pore-scale modeling of the porosity exponent that incorporates different geological processes. The evolution of m of eight synthetic samples with different particle sizes and shapes are calculated during two geological processes, i.e., compaction and cementation. The numerical results show that in dilute conditions, m is controlled by the particle shape. As the samples deviate from dilute conditions, m increases gradually due to the strong interaction between particles. When the samples are at static equilibrium, m is noticeably larger than its values at dilution condition. The numerical simulation results also show that both geological compaction and cementation induce a significant increase in m. In addition, the geometric characteristics of these samples (e.g., pore space/throat size, and their distributions) during compaction and cementation are also calculated. Preliminary analysis shows a unique correlation between the pore size broadness and porosity exponent for all eight samples. However, such a correlation is not found between m and other geometric characteristics.

Pore-scale Numerical Simulation Using Lattice Boltzmann Method for Mud Erosion in Methane Hydrate Bearing Layers

NASA Astrophysics Data System (ADS)

Yoshida, T.; Sato, T.; Oyama, H.

2014-12-01

Methane hydrates in subsea environments near Japan are believed to new natural gas resources. These methane hydrate crystals are very small and existed in the intergranular pores of sandy sediments in sand mud alternate layers. For gas production, several processes for recovering natural gas from the methane hydrate in a sedimentary reservoir have been proposed, but almost all technique are obtain dissociated gas from methane hydrates. When methane hydrates are dissociated, gas and water are existed. These gas and water are flown in pore space of sand mud alternate layers, and there is a possibility that the mud layer is eroded by these flows. It is considered that the mad erosion causes production trouble such as making skins or well instability. In this study, we carried out pore scale numerical simulation to represent mud erosion. This research aims to develop a fundamental simulation method based on LBM (Lattice Boltzmann Method). In the simulation, sand particles are generated numerically in simulation area which is approximately 200x200x200μm3. The periodic boundary condition is used except for mud layers. The water/gas flow in pore space is calculated by LBM, and shear stress distribution is obtained at the position flow interacting mud surface. From this shear stress, we consider that the driving force of mud erosion. As results, mud erosion can be reproduced numerically by adjusting the parameters such as critical shear stress. We confirmed that the simulation using LBM is appropriate for mud erosion.

Adsorption of Poly(methyl methacrylate) on Concave Al2O3 Surfaces in Nanoporous Membranes

PubMed Central

Nunnery, Grady; Hershkovits, Eli; Tannenbaum, Allen; Tannenbaum, Rina

2009-01-01

The objective of this study was to determine the influence of polymer molecular weight and surface curvature on the adsorption of polymers onto concave surfaces. Poly(methyl methacrylate) (PMMA) of various molecular weights was adsorbed onto porous aluminum oxide membranes having various pore sizes, ranging from 32 to 220 nm. The surface coverage, expressed as repeat units per unit surface area, was observed to vary linearly with molecular weight for molecular weights below ~120 000 g/mol. The coverage was independent of molecular weight above this critical molar mass, as was previously reported for the adsorption of PMMA on convex surfaces. Furthermore, the coverage varied linearly with pore size. A theoretical model was developed to describe curvature-dependent adsorption by considering the density gradient that exists between the surface and the edge of the adsorption layer. According to this model, the density gradient of the adsorbed polymer segments scales inversely with particle size, while the total coverage scales linearly with particle size, in good agreement with experiment. These results show that the details of the adsorption of polymers onto concave surfaces with cylindrical geometries can be used to calculate molecular weight (below a critical molecular weight) if pore size is known. Conversely, pore size can also be determined with similar adsorption experiments. Most significantly, for polymers above a critical molecular weight, the precise molecular weight need not be known in order to determine pore size. Moreover, the adsorption developed and validated in this work can be used to predict coverage also onto surfaces with different geometries. PMID:19415910

Measurement and Visualization of Tight Rock Exposed to CO2 Using NMR Relaxometry and MRI

PubMed Central

Wang, Haitao; Lun, Zengmin; Lv, Chengyuan; Lang, Dongjiang; Ji, Bingyu; Luo, Ming; Pan, Weiyi; Wang, Rui; Gong, Kai

2017-01-01

Understanding mechanisms of oil mobilization of tight matrix during CO2 injection is crucial for CO2 enhanced oil recovery (EOR) and sequestration engineering design. In this study exposure behavior between CO2 and tight rock of the Ordos Basin has been studied experimentally by using nuclear magnetic resonance transverse relaxation time (NMR T2) spectrum and magnetic resonance imaging (MRI) under the reservoir pressure and temperature. Quantitative analysis of recovery at the pore scale and visualization of oil mobilization are achieved. Effects of CO2 injection, exposure times and pressure on recovery performance have been investigated. The experimental results indicate that oil in all pores can be gradually mobilized to the surface of rock by CO2 injection. Oil mobilization in tight rock is time-consuming while oil on the surface of tight rock can be mobilized easily. CO2 injection can effectively mobilize oil in all pores of tight rock, especially big size pores. This understanding of process of matrix exposed to CO2 could support the CO2 EOR in tight reservoirs. PMID:28281697

Tortuosity measurement and the effects of finite pulse widths on xenon gas diffusion NMR studies of porous media

NASA Technical Reports Server (NTRS)

Mair, R. W.; Hurlimann, M. D.; Sen, P. N.; Schwartz, L. M.; Patz, S.; Walsworth, R. L.

2001-01-01

We have extended the utility of NMR as a technique to probe porous media structure over length scales of approximately 100-2000 microm by using the spin 1/2 noble gas 129Xe imbibed into the system's pore space. Such length scales are much greater than can be probed with NMR diffusion studies of water-saturated porous media. We utilized Pulsed Gradient Spin Echo NMR measurements of the time-dependent diffusion coefficient, D(t), of the xenon gas filling the pore space to study further the measurements of both the pore surface-area-to-volume ratio, S/V(p), and the tortuosity (pore connectivity) of the medium. In uniform-size glass bead packs, we observed D(t) decreasing with increasing t, reaching an observed asymptote of approximately 0.62-0.65D(0), that could be measured over diffusion distances extending over multiple bead diameters. Measurements of D(t)/D(0) at differing gas pressures showed this tortuosity limit was not affected by changing the characteristic diffusion length of the spins during the diffusion encoding gradient pulse. This was not the case at the short time limit, where D(t)/D(0) was noticeably affected by the gas pressure in the sample. Increasing the gas pressure, and hence reducing D(0) and the diffusion during the gradient pulse served to reduce the previously observed deviation of D(t)/D(0) from the S/V(p) relation. The Pade approximation is used to interpolate between the long and short time limits in D(t). While the short time D(t) points lay above the interpolation line in the case of small beads, due to diffusion during the gradient pulse on the order of the pore size, it was also noted that the experimental D(t) data fell below the Pade line in the case of large beads, most likely due to finite size effects.

Smooth DNA Transport through a Narrowed Pore Geometry

PubMed Central

Carson, Spencer; Wilson, James; Aksimentiev, Aleksei; Wanunu, Meni

2014-01-01

Voltage-driven transport of double-stranded DNA through nanoscale pores holds much potential for applications in quantitative molecular biology and biotechnology, yet the microscopic details of translocation have proven to be challenging to decipher. Earlier experiments showed strong dependence of transport kinetics on pore size: fast regular transport in large pores (> 5 nm diameter), and slower yet heterogeneous transport time distributions in sub-5 nm pores, which imply a large positional uncertainty of the DNA in the pore as a function of the translocation time. In this work, we show that this anomalous transport is a result of DNA self-interaction, a phenomenon that is strictly pore-diameter dependent. We identify a regime in which DNA transport is regular, producing narrow and well-behaved dwell-time distributions that fit a simple drift-diffusion theory. Furthermore, a systematic study of the dependence of dwell time on DNA length reveals a single power-law scaling of 1.37 in the range of 35–20,000 bp. We highlight the resolution of our nanopore device by discriminating via single pulses 100 and 500 bp fragments in a mixture with >98% accuracy. When coupled to an appropriate sequence labeling method, our observation of smooth DNA translocation can pave the way for high-resolution DNA mapping and sizing applications in genomics. PMID:25418307

Three-dimensional video imaging of drainage and imbibition processes in model porous medium

NASA Astrophysics Data System (ADS)

Sharma, Prerna; Aswathi, P.; Sane, Anit; Ghosh, Shankar; Bhattacharya, Sabyasachi

2011-03-01

We report experimental results where we have performed three dimensional video imaging of the displacement of an oil phase by an aqueous phase and vice versa in a model porous medium. The stability of the oil water interface was studied as a function of their viscosity ratios, the wettability of the porous medium and the variation in the pore size distribution. Our experiments captures the pore scale information of the displacement process and its role in determining the long time structure of the interface.

[Preparation of nano-nacre artificial bone].

PubMed

Chen, Jian-ting; Tang, Yong-zhi; Zhang, Jian-gang; Wang, Jian-jun; Xiao, Ying

2008-12-01

To assess the improvements in the properties of nano-nacre artificial bone prepared on the basis of nacre/polylactide acid composite artificial bone and its potential for clinical use. The compound of nano-scale nacre powder and poly-D, L-lactide acid (PDLLA) was used to prepare the cylindrical hollow artificial bone, whose properties including raw material powder scale, pore size, porosity and biomechanical characteristics were compared with another artificial bone made of micron-scale nacre powder and PDLLA. Scanning electron microscope showed that the average particle size of the nano-nacre powder was 50.4-/+12.4 nm, and the average pore size of the artificial bone prepared using nano-nacre powder was 215.7-/+77.5 microm, as compared with the particle size of the micron-scale nacre powder of 5.0-/+3.0 microm and the pore size of the resultant artificial bone of 205.1-/+72.0 microm. The porosities of nano-nacre artificial bone and the micron-nacre artificial bone were (65.4-/+2.9)% and (53.4-/+2.2)%, respectively, and the two artificial bones had comparable compressive strength and Young's modulus, but the flexural strength of the nano-nacre artificial bone was lower than that of the micro-nacre artificial bone. The nano-nacre artificial bone allows better biodegradability and possesses appropriate pore size, porosity and biomechanical properties for use as a promising material in bone tissue engineering.

Kinetic roughening and porosity scaling in film growth with subsurface lateral aggregation.

PubMed

Reis, F D A Aarão

2015-06-01

We study surface and bulk properties of porous films produced by a model in which particles incide perpendicularly to a substrate, interact with deposited neighbors in its trajectory, and aggregate laterally with probability of order a at each position. The model generalizes ballisticlike models by allowing attachment to particles below the outer surface. For small values of a, a crossover from uncorrelated deposition (UD) to correlated growth is observed. Simulations are performed in 1+1 and 2+1 dimensions. Extrapolation of effective exponents and comparison of roughness distributions confirm Kardar-Parisi-Zhang roughening of the outer surface for a>0. A scaling approach for small a predicts crossover times as a(-2/3) and local height fluctuations as a(-1/3) at the crossover, independent of substrate dimension. These relations are different from all previously studied models with crossovers from UD to correlated growth due to subsurface aggregation, which reduces scaling exponents. The same approach predicts the porosity and average pore height scaling as a(1/3) and a(-1/3), respectively, in good agreement with simulation results in 1+1 and 2+1 dimensions. These results may be useful for modeling samples with desired porosity and long pores.

Experimental and modeling study of Newtonian and non-Newtonian fluid flow in pore network micromodels.

PubMed

Perrin, Christian L; Tardy, Philippe M J; Sorbie, Ken S; Crawshaw, John C

2006-03-15

The in situ rheology of polymeric solutions has been studied experimentally in etched silicon micromodels which are idealizations of porous media. The rectangular channels in these etched networks have dimensions typical of pore sizes in sandstone rocks. Pressure drop/flow rate relations have been measured for water and non-Newtonian hydrolyzed-polyacrylamide (HPAM) solutions in both individual straight rectangular capillaries and in networks of such capillaries. Results from these experiments have been analyzed using pore-scale network modeling incorporating the non-Newtonian fluid mechanics of a Carreau fluid. Quantitative agreement is seen between the experiments and the network calculations in the Newtonian and shear-thinning flow regions demonstrating that the 'shift factor,'alpha, can be calculated a priori. Shear-thickening behavior was observed at higher flow rates in the micromodel experiments as a result of elastic effects becoming important and this remains to be incorporated in the network model.

Effects of management and pore characteristics on organic matter composition of macroaggregates: evidence from characterization of organic matter and imaging: Pore characteristics and OM composition of macroaggregates

DOE Office of Scientific and Technical Information (OSTI.GOV)

Toosi, E. R.; Kravchenko, A. N.; Mao, J.

Macroaggregates are of interest because of their fast response to land management and their role in the loss or restoration of soil organic carbon (SOC). The study included two experiments. In Experiment I, we investigated the effect of long-term (27 years) land management on the chemical composition of organic matter (OM) of macroaggregates. Macroaggregates were sampled from topsoil under conventional cropping, cover cropping and natural succession systems. The OM of macroaggregates from conventional cropping was more decomposed than that of cover cropping and especially natural succession, based on larger δ 15N values and decomposition indices determined by multiple magic-angle spinningmore » nuclear magnetic resonance ( 13C CP/MAS NMR) and Fourier transform infrared (FTIR) spectroscopy. Previous research at the sites studied suggested that this was mainly because of reduced diversity and activity of the decomposer community, change in nutrient stoichiometry from fertilization and contrasting formation pathways of macroaggregates in conventional cropping compared with cover cropping and, specifically, natural succession. In Experiment II, we investigated the relation between OM composition and pore characteristics of macroaggregates. Macroaggregates from the natural succession system only were studied. We determined 3-D pore-size distribution of macroaggregates with X-ray microtomography, for which we cut the macroaggregates into sections that had contrasting dominant pore sizes. Then, we characterized the OM of macroaggregate sections with FTIR and δ15N methods. The results showed that within a macroaggregate, the OM was less decomposed in areas where the small (13–32 µm) or large (136–260 µm) pores were abundant. This was attributed to the role of large pores in supplying fresh OM and small pores in the effective protection of OM in macroaggregates. Previous research at the site studied had shown increased abundance of large and small intra-aggregate pores following adoption of less intensive management systems. It appears that land management can alter the OM composition of macroaggregates, partly by the regulation of OM turnover at the intra-aggregate scale.« less

Generalized Hydrodynamic Treatment of the Interplay between Restricted Transport and Catalytic Reactions in Nanoporous Materials

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ackerman, David M.; Wang, Jing; Evans, James W.

2012-05-30

Behavior of catalytic reactions in narrow pores is controlled by a delicate interplay between fluctuations in adsorption-desorption at pore openings, restricted diffusion, and reaction. This behavior is captured by a generalized hydrodynamic formulation of appropriate reaction-diffusion equations (RDE). These RDE incorporate an unconventional description of chemical diffusion in mixed-component quasi-single-file systems based on a refined picture of tracer diffusion for finite-length pores. The RDE elucidate the nonexponential decay of the steady-state reactant concentration into the pore and the non-mean-field scaling of the reactant penetration depth.

Generalized hydrodynamic treatment of the interplay between restricted transport and catalytic reactions in nanoporous materials.

PubMed

Ackerman, David M; Wang, Jing; Evans, James W

2012-06-01

Behavior of catalytic reactions in narrow pores is controlled by a delicate interplay between fluctuations in adsorption-desorption at pore openings, restricted diffusion, and reaction. This behavior is captured by a generalized hydrodynamic formulation of appropriate reaction-diffusion equations (RDE). These RDE incorporate an unconventional description of chemical diffusion in mixed-component quasi-single-file systems based on a refined picture of tracer diffusion for finite-length pores. The RDE elucidate the nonexponential decay of the steady-state reactant concentration into the pore and the non-mean-field scaling of the reactant penetration depth.

Characterizing 3-D flow velocity in evolving pore networks driven by CaCO3 precipitation and dissolution

NASA Astrophysics Data System (ADS)

Chojnicki, K. N.; Yoon, H.; Martinez, M. J.

2015-12-01

Understanding reactive flow in geomaterials is important for optimizing geologic carbon storage practices, such as using pore space efficiently. Flow paths can be complex in large degrees of geologic heterogeneities across scales. In addition, local heterogeneity can evolve as reactive transport processes alter the pore-scale morphology. For example, dissolved carbon dioxide may react with minerals in fractured rocks, confined aquifers, or faults, resulting in heterogeneous cementation (and/or dissolution) and evolving flow conditions. Both path and flow complexities are important and poorly characterized, making it difficult to determine their evolution with traditional 2-D transport models. Here we characterize the development of 3-D pore-scale flow with an evolving pore configuration due to calcium carbonate (CaCO3) precipitation and dissolution. A simple pattern of a microfluidic pore network is used initially and pore structures will become more complex due to precipitation and dissolution processes. At several stages of precipitation and dissolution, we directly visualize 3-D velocity vectors using micro particle image velocimetry and a laser scanning confocal microscope. Measured 3-D velocity vectors are then compared to 3-D simulated flow fields which will be used to simulate reactive transport. Our findings will highlight the importance of the 3-D flow dynamics and its impact on estimating reactive surface area over time. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000. This material is based upon work supported as part of the Center for Frontiers of Subsurface Energy Security, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award Number DE-SC0001114.

Comparison of Effective Medium Schemes For Seismic Velocities in Cracked Anisotropic Rock

NASA Astrophysics Data System (ADS)

Morshed, S.; Chesnokov, E.

2017-12-01

Understanding of elastic properties of reservoir rock is necessary for meaningful interpretation and analysis of seismic measurements. The elastic properties of a rock are controlled by the microstructural properties such as mineralogical composition, pore and crack distribution, texture and pore connectivity. However, seismic scale is much larger than microstructure scale. Understanding of macroscopic properties at relevant seismic scale (e.g. borehole sonic data) comes from effective medium theory (EMT). However, most of the effective medium theories fail at high crack density as the interactions of strain fields of the cracks can't be ignored. We compare major EMT schemes from low to high crack density. While at low crack density all method gives similar results, at high crack density they differ significantly. Then, we focus on generalized singular approximation (GSA) and effective field (EF) method as they allow cracks beyond the limit of dilute concentrations. Additionally, we use grain contact (GC) method to examine the stiffness constants of the rock matrix. We prepare simple models of a multiphase media containing low to high concentrations of isolated pores. Randomly oriented spherical pores and horizontally oriented ellipsoidal (aspect ratio =0.1) pores have been considered. For isolated spherical pores, all the three methods show exactly same or similar results. However, inclusion interactions are different in different directions in case of horizontal ellipsoidal pores and individual stiffness constants differ greatly from one method to another at different crack density. Stiffness constants remain consistent in GSA method whereas some components become unusual in EF method at a higher crack density (>0.15). Finally, we applied GSA method to interpret ultrasonic velocities of core samples. Mineralogical composition from X-ray diffraction (XRD) data and lab measured porosity data have been utilized. Both compressional and shear wave velocities from GSA method show good fit with the lab measured velocities.

Modelling the influence of pore size on the response of materials to infrared lasers An application to human enamel

NASA Astrophysics Data System (ADS)

Vila Verde, A.; Ramos, Marta M. D.

2005-07-01

We present an analytical model for a ceramic material (hydroxyapatite, HA) containing nanometre-scale water pores, and use it to estimate the pressure at the pore as a function of temperature at the end of a single 0.35 μs laser pulse by Er:YAG (2.94 μm) and CO 2 (10.6 μm) lasers. Our results suggest that the pressure at the pore is directly related to pore temperature, and that very high pressures can be generated simply by the thermal expansion of liquid water. Since the temperature reached in the pores at the end of the laser pulse is a strong function of pore size for Er:YAG lasers, but is independent of pore size for CO 2 lasers, our present results provide a possible explanation for the fact that human dental enamel threshold ablation fluences vary more for Er:YAG lasers than for CO 2 lasers. This suggests that experimentalists should analyse their results accounting for factors, like age or type of tooth, that may change the pore size distribution in their samples.

Methane and CO2 Adsorption and Transport in Carbon-based Systems from Experiments and Molecular Simulation

NASA Astrophysics Data System (ADS)

Wilcox, Jennifer; Firouzi, Mahnaz; Rupp, Erik; Haghapanah, Reza; Wang, Beibei

2013-04-01

Carbon capture and sequestration is one strategy that could potentially mitigate gigatons of CO2 emissions per year; however, technical obstacles have thus far hindered wide-scale deployment of this strategy. To design efficient and reliable strategies for either carbon capture or sequestration at the full-scale, one needs to understand the chemical and physical properties of CO2 and its interaction with its local surroundings at the molecular-scale. To investigate the chemical and physical properties of CO2 and its local surroundings at the molecular-scale, surface characterization studies are carried out alongside theoretical model efforts. Experimental investigation of CO2 interactions with organic-based porous materials ranging in complexity from functionalized graphene and activated carbon to various-rank coal and gas shale samples to create a set of realistic models that take into account both surface and pore heterogeneity. Integration of theory and experiments takes place to allow for the relevant physics at the molecular-level to be revealed. Determining adsorption and transport phenomena of CO2 (and mixtures, including H2O, and CH4) within the model pore systems can be used to understand the complex pore matrices of carbon-based sorbents, coal, and the organic components of gas shale that are crucial to determining their carbon capture or sequestration potential. Non-equilibrium molecular dynamics (NEMD) simulations of pure carbon dioxide, methane, helium and their mixtures have been carried out in carbon slit pores to investigate gas slippage and Klinkenberg effects in the organic matrices of coal and gas shale rocks. NEMD techniques are ideally suited for the experimental situation in which an external driving force, such as a chemical potential or pressure gradient, are applied on the system. Simulations have been conducted to determine the effect of pore size and exposure to an external potential on the velocity profile and slip-stick boundary conditions. The simulations indicate that molecule-wall collisions influence the velocity profile, which deviates significantly from the Navier-Stokes hydrodynamic prediction for micro and mesopores. Also, the shape of the velocity profile is found to be independent of the applied pressure gradient in micropores. The results indicate that the velocity profile is uniform for pore sizes less than 2 nm (micropores). As pore sizes increase to 10 nm, parabolic profiles are observed due to the reduced interaction of gas molecules with the pore walls. Interestingly, in small pores unlike in large pores, the gas velocity at the walls is non-zero and predicted gas transport is somewhat enhanced as the gas flow transitions from a parabolic velocity profile to plug-flow. In addition, a 3-D pore network, representative of porous carbon-based materials, has been generated atomistically using the Voronoi tessellation method. Simulations have been carried out to determine the effect of the pore structure and modeled viscosity on permeability and Klinkenberg parameters. The use of the bulk-phase viscosity for estimating the permeability of CO2 in units of Darcy in a 3-D micropore network is not an appropriate assumption as it significantly underestimates the CO2 permeability given that CO2 is an adsorbing gas with strong pore wall interactions. On the other hand, since the transport properties of CH4 are less influenced by the pore walls compared with CO2, the use of the bulk-phase CH4 viscosity estimates are a reasonable assumption. The application of this work is to advance our understanding of gas transport and to provide insight into mechanisms of gas-surface interactions in the complex natural systems such as gas shale so that we can make accurate capacity estimates in addition to assisting in enhancing natural gas recovery from these systems. These results will potentially have important implications on CO2 adsorption and transport in carbon-based materials and geologic formations and may provide an understanding of the limitations of the use of bulk-phase fluid viscosities to model transport properties for nanoconfined fluids.

Pore-Scale Geochemical Reactivity Associated with CO2 Storage: New Frontiers at the Fluid-Solid Interface.

PubMed

Noiriel, Catherine; Daval, Damien

2017-04-18

The reactivity of carbonate and silicate minerals is at the heart of porosity and pore geometry changes in rocks injected with CO 2 , which ultimately control the evolution of flow and transport properties of fluids in porous and/or fractured geological reservoirs. Modeling the dynamics of CO 2 -water-rock interactions is challenging because of the resulting large geochemical disequilibrium, the reservoir heterogeneities, and the large space and time scales involved in the processes. In particular, there is a lack of information about how the macroscopic properties of a reservoir, e.g., the permeability, will evolve as a result of geochemical reactions at the molecular scale. Addressing this point requires a fundamental understanding of how the microstructures influence the macroscopic properties of rocks. The pore scale, which ranges from a few nanometers to centimeters, has stood out as an essential scale of observation of geochemical processes in rocks. Transport or surface reactivity limitations due to the pore space architecture, for instance, are best described at the pore scale itself. It can be also considered as a mesoscale for aggregating and increasing the gain of fundamental understanding of microscopic interfacial processes. Here we focus on the potential application of a combination of physicochemical measurements coupled with nanoscale and microscale imaging techniques during laboratory experiments to improve our understanding of the physicochemical mechanisms that occur at the fluid-solid interface and the dynamics of the coupling between the geochemical reactions and flow and transport modifications at the pore scale. Imaging techniques such as atomic force microscopy, vertical scanning interferometry, focused ion beam transmission electron microscopy, and X-ray microtomography, are ideal for investigating the reactivity dynamics of these complex materials. Minerals and mineral assemblages, i.e., rocks, exhibit heterogeneous and anisotropic reactivity, which challenges the continuum description of porous media and assumptions required for reactive transport modeling at larger scales. The conventional approach, which consists of developing dissolution rate laws normalized to the surface area, should be revisited to account for both the anisotropic crystallographic structure of minerals and the transport of chemical species near the interface, which are responsible for the intrinsic evolution of the mineral dissolution rate as the reaction progresses. In addition, the crystal morphology and the mineral assemblage composition, texture, and structural heterogeneities are crucial in determining whether the permeability and transport properties of the reservoir will be altered drastically or maintain the sealing properties required to ensure the safe sequestration of CO 2 for hundreds of years. Investigating the transport properties in nanometer- to micrometer-thick amorphous Si-rich surface layers (ASSLs), which develop at the fluid-mineral interface in silicates, provides future direction, as ASSLs may prevent contact between the dissolving solids and the pore fluid, potentially inhibiting the dissolution/carbonation process. Equally, at a larger scale, the growth of micrometer- to millimeter-thick alteration layers, which result from the difference in reactivity between silicates and carbonates, slows the transport in the vicinity of the fluid-solid interface in polymineralic rocks, thus limiting the global reactivity of the carbonate matrix. In contrast, in pure limestone, the global reactivity of the monomineralic rock decreases because the flow localization promotes the local reactivity within the forming channels, thus enhancing permeability changes compared with more homogeneous dissolution of the rock matrix. These results indicate that the transformation of the rock matrix should control the evolution of the transport properties in reservoirs injected with CO 2 to the same extent as the intrinsic chemical reactivity of the minerals and the reservoir hydrodynamics. This process, which is currently not captured by large-scale modeling of reactive transport, should benefit from the increasing capabilities of noninvasive and nondestructive characterization tools for pore-scale processes, ultimately constraining reactive transport modeling and improving the reliability of predictions.

Physically-based model of soil hydraulic properties accounting for variable contact angle and its effect on hysteresis

NASA Astrophysics Data System (ADS)

Diamantopoulos, Efstathios; Durner, Wolfgang

2013-09-01

The description of soil water movement in the unsaturated zone requires the knowledge of the soil hydraulic properties, i.e. the water retention and the hydraulic conductivity function. A great amount of parameterizations for this can be found in the literature, the majority of which represent the complex pore space of soils as a bundle of cylindrical capillary tubes of various sizes. The assumption of zero contact angles between water and surface of the grains is also made. However, these assumptions limit the predictive capabilities of these models, leading often to errors in the prediction of water dynamics in soils. We present a pore-scale analysis for equilibrium liquid configuration in angular pores taking pore-scale hysteresis and the effect of contact angle into account. Furthermore, we propose a derivation of the hydraulic conductivity function, again as a function of the contact angle. An additional parameter was added to the conductivity function in order take into account effects which are not included in the analysis. Finally, we upscale our model from the pore to the sample scale by assuming a gamma statistical distribution of the pore sizes. Closed-form expressions are derived for both water retention and conductivity functions. The new model was tested against experimental data from multistep inflow/outflow (MSI/MSO) experiments for a sandy material. They were conducted using ethanol and water as the wetting liquid. Ethanol was assumed to form a zero contact angle with the soil grains. By keeping constant the parameters fitted from the ethanol MSO experiment we could predict the ethanol MSI dynamics based on our theory. Furthermore, by keeping constant the pore size distribution parameters from the ethanol experiments we could also predict very well the water dynamics for the MSO experiment. Lastly, we could predict the imbibition dynamics for the water MSI experiment by introducing a finite value of the contact angle. Most importantly, the predictions for both ethanol and water MSI/MSO dynamics were made by assuming a unique pore-size distribution.

Critiquing ';pore connectivity' as basis for in situ flow in geothermal systems

NASA Astrophysics Data System (ADS)

Kenedi, C. L.; Leary, P.; Malin, P.

2013-12-01

Geothermal system in situ flow systematics derived from detailed examination of grain-scale structures, fabrics, mineral alteration, and pore connectivity may be extremely misleading if/when extrapolated to reservoir-scale flow structure. In oil/gas field clastic reservoir operations, it is standard to assume that small scale studies of flow fabric - notably the Kozeny-Carman and Archie's Law treatments at the grain-scale and well-log/well-bore sampling of formations/reservoirs at the cm-m scale - are adequate to define the reservoir-scale flow properties. In the case of clastic reservoirs, however, a wide range of reservoir-scale data wholly discredits this extrapolation: Well-log data show that grain-scale fracture density fluctuation power scales inversely with spatial frequency k, S(k) ~ 1/k^β, 1.0 < β < 1.2, 1cycle/km < k < 1cycle/cm; the scaling is a ';universal' feature of well-logs (neutron porosity, sonic velocity, chemical abundance, mass density, resistivity, in many forms of clastic rock and instances of shale bodies, for both horizontal and vertical wells). Grain-scale fracture density correlates with in situ porosity; spatial fluctuations of porosity φ in well-core correlate with spatial fluctuations in the logarithm of well-core permeability, δφ ~ δlog(κ) with typical correlation coefficient ~ 85%; a similar relation is observed in consolidating sediments/clays, indicating a generic coupling between fluid pressure and solid deformation at pore sites. In situ macroscopic flow systems are lognormally distributed according to κ ~ κ0 exp(α(φ-φ0)), α >>1 an empirical parameter for degree of in situ fracture connectivity; the lognormal distribution applies to well-productivities in US oil fields and NZ geothermal fields, ';frack productivity' in oil/gas shale body reservoirs, ore grade distributions, and trace element abundances. Although presently available evidence for these properties in geothermal reservoirs is limited, there are indications that geothermal system flow essentially obeys the same ';universal' in situ flow rules as does clastic rock: Well-log data from Los Azufres, MX, show power-law scaling S(k) ~ 1/k^β, 1.2 < β < 1.4, for spatial frequency range 2cycles/km to 0.5cycle/m; higher β-values are likely due to the relatively fresh nature of geothermal systems; Well-core at Bulalo (PH) and Ohaaki (NZ) show statistically significant spatial correlation, δφ ~ δlog(κ) Well productivity at Ohaaki/Ngawha (NZ) and in geothermal systems elsewhere are lognormally distributed; K/Th/U abundances lognormally distributed in Los Azufres well-logs We therefore caution that small-scale evidence for in situ flow fabric in geothermal systems that is interpreted in terms of ';pore connectivity' may in fact not reflect how small-scale chemical processes are integrated into a large-scale geothermal flow structure. Rather such small scale studies should (perhaps) be considered in term of the above flow rules. These flow rules are easily incorporated into standard flow simulation codes, in particular the OPM = Open Porous Media open-source industry-standard flow code. Geochemical transport data relevant to geothermal systems can thus be expected to be well modeled by OPM or equivalent (e.g., INL/LANL) codes.

Proton Diffusion through Bilayer Pores

DOE PAGES

McDaniel, Jesse G.; Yethiraj, Arun

2017-09-26

The transport of protons through channels in complex environments is important in biology and materials science. In this work, we use multistate empirical valence bond simulations to study proton transport within a well-defined bilayer pore in a lamellar L β phase lyotropic liquid crystal (LLC). The LLC is formed from the self-assembly of dicarboxylate gemini surfactants in water, and a bilayer-spanning pore of radius of approximately 3–5 Å results from the uneven partitioning of surfactants between the two leaflets of the lamella. Local proton diffusion within the pore is significantly faster than diffusion at the bilayer surface, which is duemore » to the greater hydrophobicity of the surfactant/water interface within the pore. Proton diffusion proceeds by surface transport along exposed hydrophobic pockets at the surfactant/water interface and depends on the continuity of hydronium–water hydrogen bond networks. At the bilayer surface, there is a reduced fraction of the “Zundel” intermediates that are central to the Grotthuss transport mechanism, whereas the fraction of these species within the bilayer pore is similar to that in bulk water. Our results demonstrate that the chemical nature of the confining interface, in addition to confinement length scale, is an important determiner of local proton transport in nanoconfined aqueous environments.« less

A functional relation for field-scale nonaqueous phase liquid dissolution developed using a pore network model

USGS Publications Warehouse

Dillard, L.A.; Essaid, H.I.; Blunt, M.J.

2001-01-01

A pore network model with cubic chambers and rectangular tubes was used to estimate the nonaqueous phase liquid (NAPL) dissolution rate coefficient, Kdissai, and NAPL/water total specific interfacial area, ai. Kdissai was computed as a function of modified Peclet number (Pe???) for various NAPL saturations (SN) and ai during drainage and imbibition and during dissolution without displacement. The largest contributor to ai was the interfacial area in the water-filled corners of chambers and tubes containing NAPL. When Kdissai was divided by ai, the resulting curves of dissolution coefficient, Kdiss versus Pe??? suggested that an approximate value of Kdiss could be obtained as a weak function of hysteresis or SN. Spatially and temporally variable maps of Kdissai calculated using the network model were used in field-scale simulations of NAPL dissolution. These simulations were compared to simulations using a constant value of Kdissai and the empirical correlation of Powers et al. [Water Resour. Res. 30(2) (1994b) 321]. Overall, a methodology was developed for incorporating pore-scale processes into field-scale prediction of NAPL dissolution. Copyright ?? 2001 .

Controls on the physical properties of gas-hydrate-bearing sediments because of the interaction between gas hydrate and porous media

USGS Publications Warehouse

Lee, Myung W.; Collett, Timothy S.

2005-01-01

Physical properties of gas-hydrate-bearing sediments depend on the pore-scale interaction between gas hydrate and porous media as well as the amount of gas hydrate present. Well log measurements such as proton nuclear magnetic resonance (NMR) relaxation and electromagnetic propagation tool (EPT) techniques depend primarily on the bulk volume of gas hydrate in the pore space irrespective of the pore-scale interaction. However, elastic velocities or permeability depend on how gas hydrate is distributed in the pore space as well as the amount of gas hydrate. Gas-hydrate saturations estimated from NMR and EPT measurements are free of adjustable parameters; thus, the estimations are unbiased estimates of gas hydrate if the measurement is accurate. However, the amount of gas hydrate estimated from elastic velocities or electrical resistivities depends on many adjustable parameters and models related to the interaction of gas hydrate and porous media, so these estimates are model dependent and biased. NMR, EPT, elastic-wave velocity, electrical resistivity, and permeability measurements acquired in the Mallik 5L-38 well in the Mackenzie Delta, Canada, show that all of the well log evaluation techniques considered provide comparable gas-hydrate saturations in clean (low shale content) sandstone intervals with high gas-hydrate saturations. However, in shaly intervals, estimates from log measurement depending on the pore-scale interaction between gas hydrate and host sediments are higher than those estimates from measurements depending on the bulk volume of gas hydrate.

Effect of sub-pore scale morphology of biological deposits on porous media flow properties

NASA Astrophysics Data System (ADS)

Ghezzehei, T. A.

2012-12-01

Biological deposits often influence fluid flow by altering the pore space morphology and related hydrologic properties such as porosity, water retention characteristics, and permeability. In most coupled-processes models changes in porosity are inferred from biological process models using mass-balance. The corresponding evolution of permeability is estimated using (semi-) empirical porosity-permeability functions such as the Kozeny-Carman equation or power-law functions. These equations typically do not account for the heterogeneous spatial distribution and morphological irregularities of the deposits. As a result, predictions of permeability evolution are generally unsatisfactory. In this presentation, we demonstrate the significance of pore-scale deposit distribution on porosity-permeability relations using high resolution simulations of fluid flow through a single pore interspersed with deposits of varying morphologies. Based on these simulations, we present a modification to the Kozeny-Carman model that accounts for the shape of the deposits. Limited comparison with published experimental data suggests the plausibility of the proposed conceptual model.

Pore-scale modeling of saturated permeabilities in random sphere packings.

PubMed

Pan, C; Hilpert, M; Miller, C T

2001-12-01

We use two pore-scale approaches, lattice-Boltzmann (LB) and pore-network modeling, to simulate single-phase flow in simulated sphere packings that vary in porosity and sphere-size distribution. For both modeling approaches, we determine the size of the representative elementary volume with respect to the permeability. Permeabilities obtained by LB modeling agree well with Rumpf and Gupte's experiments in sphere packings for small Reynolds numbers. The LB simulations agree well with the empirical Ergun equation for intermediate but not for small Reynolds numbers. We suggest a modified form of Ergun's equation to describe both low and intermediate Reynolds number flows. The pore-network simulations agree well with predictions from the effective-medium approximation but underestimate the permeability due to the simplified representation of the porous media. Based on LB simulations in packings with log-normal sphere-size distributions, we suggest a permeability relation with respect to the porosity, as well as the mean and standard deviation of the sphere diameter.

Bio-inspired Murray materials for mass transfer and activity

PubMed Central

Zheng, Xianfeng; Shen, Guofang; Wang, Chao; Li, Yu; Dunphy, Darren; Hasan, Tawfique; Brinker, C. Jeffrey; Su, Bao-Lian

2017-01-01

Both plants and animals possess analogous tissues containing hierarchical networks of pores, with pore size ratios that have evolved to maximize mass transport and rates of reactions. The underlying physical principles of this optimized hierarchical design are embodied in Murray's law. However, we are yet to realize the benefit of mimicking nature's Murray networks in synthetic materials due to the challenges in fabricating vascularized structures. Here we emulate optimum natural systems following Murray's law using a bottom-up approach. Such bio-inspired materials, whose pore sizes decrease across multiple scales and finally terminate in size-invariant units like plant stems, leaf veins and vascular and respiratory systems provide hierarchical branching and precise diameter ratios for connecting multi-scale pores from macro to micro levels. Our Murray material mimics enable highly enhanced mass exchange and transfer in liquid–solid, gas–solid and electrochemical reactions and exhibit enhanced performance in photocatalysis, gas sensing and as Li-ion battery electrodes. PMID:28382972

Generation of random microstructures and prediction of sound velocity and absorption for open foams with spherical pores.

PubMed

Zieliński, Tomasz G

2015-04-01

This paper proposes and discusses an approach for the design and quality inspection of the morphology dedicated for sound absorbing foams, using a relatively simple technique for a random generation of periodic microstructures representative for open-cell foams with spherical pores. The design is controlled by a few parameters, namely, the total open porosity and the average pore size, as well as the standard deviation of pore size. These design parameters are set up exactly and independently, however, the setting of the standard deviation of pore sizes requires some number of pores in the representative volume element (RVE); this number is a procedure parameter. Another pore structure parameter which may be indirectly affected is the average size of windows linking the pores, however, it is in fact weakly controlled by the maximal pore-penetration factor, and moreover, it depends on the porosity and pore size. The proposed methodology for testing microstructure-designs of sound absorbing porous media applies the multi-scale modeling where some important transport parameters-responsible for sound propagation in a porous medium-are calculated from microstructure using the generated RVE, in order to estimate the sound velocity and absorption of such a designed material.

A novel approach to model hydraulic and electrical conductivity in fractal porous media

NASA Astrophysics Data System (ADS)

Ghanbarian, B.; Daigle, H.; Sahimi, M.

2014-12-01

Accurate prediction of conductivity in partially-saturated porous media has broad applications in various phenomena in porous media, and has been studied intensively since the 1940s by petroleum, chemical and civil engineers, and hydrologists. Many of the models developed in the past are based on the bundle of capillary tubes. In addition, pore network models have also been developed for simulating multiphase fluid flow in porous media and computing the conductivity in unsaturated porous media. In this study, we propose a novel approach using concepts from the effective-medium approximation (EMA) and percolation theory to model hydraulic and electrical conductivity in fractal porous media whose pore-size distributions exhibit power-law scaling. In our approach, the EMA, originally developed for predicting electrical conductivity of composite materials, is used to predict the effective conductivity, from complete saturation to some intermediate water content that represents a crossover point. Below the crossover water content, but still above a critical saturation (percolation threshold), a universal scaling predicted by percolation theory, a power law that expresses the dependence of the conductivity on the water content (less a critical water saturation) with an exponent of 2, is invoked to describe the effective conductivity. In order to evaluate the accuracy of the approach, experimental data were used from the literature. The predicted hydraulic conductivities for most cases are in excellent agreement with the data. In a few cases the theory underestimates the hydraulic conductivities, which correspond to porous media with very broad pore-size distribution in which the largest pore radius is more than 7 orders of magnitude greater than the smallest one. The approach is also used to predict the saturation dependence of the electrical conductivity for experiments in which capillary pressure data are available. The results indicate that the universal scaling of the electrical conductivity is valid from the percolation threshold all the way up to the complete saturation point. Our results confirm those reported previously by Ewing and Hunt (2006) who argued that the electrical conductivity should follow universal scaling over the entire range of saturation.

Soil Pore Characteristics, an Underappreciated Regulatory Factor in GHGs Emission and C Stabilization

NASA Astrophysics Data System (ADS)

Toosi, E. R.; Yu, J.; Doane, T. A.; Guber, A.; Rivers, M. L.; Marsh, T. L.; Ali, K.; Kravchenko, A. N.

2015-12-01

Enduring challenges in understanding soil organic matter (SOM) stability and emission of greenhouse gases (GHGs) from soil stem from complexities of soil processes, many of which occur at micro-scales. The goal of this study is to evaluate the interactive effects soil pore characteristics, soil moisture levels, inherent SOM levels and properties, and substrate quality, on GHGs emission, and accelerated decomposition of native SOM following addition of fresh substrate i.e. priming. Our core hypothesis is that soil pore characteristics play a major role as a mediator in (i) the decomposition of organic matter regardless of its source (i.e. litter vs. native SOM) or substrate quality, as well as in (ii) GHGs emissions. Samples with prevalence of small (<10 μm) vs. large (>30 μm) pores were prepared from soils with similar properties but under long-term contrasting management. The samples were incubated (110 d) at low and optimum soil moisture conditions after addition of high quality (13C-soybean) and low quality (13C-corn) substrate. Headspace gas was analyzed for 13C-CO2 and GHGs on a regularly basis (day 1, 3, 7, 14, 24, 36, 48, 60, 72, 90, and 110). Selected samples were scanned at the early stage of decomposition (7, 14, 24 d) at 2-6 μm resolutions using X-ray computed μ tomography in order to: (1) quantify soil pore characteristics; (2) visualize and quantify distribution of soil moisture within samples of different pore characteristics; and (3) to visualize and measure losses of decomposing plant residue. Initial findings indicate that, consistent with our hypotheses, pore characteristics influenced GHGs emission, and intensity and pattern of plant residue decomposition. The importance of pores was highly pronounced in presence of added plant residue where greater N2O emission occurred in samples with dominant large pores, in contrast to CO2. Further findings will be discussed upon completion of the study and analysis of the results.

Direct Numerical Simulation of Liquid Transport Through Fibrous Porous Media

NASA Astrophysics Data System (ADS)

Palakurthi, Nikhil Kumar

Fluid flow through fibrous media occurs in many industrial processes, including, but not limited, to fuel cell technology, drug delivery patches, sanitary products, textile reinforcement, filtration, heat exchangers, and performance fabrics. Understanding the physical processes involved in fluid flow through fibrous media is essential for their characterization as well as for the optimization and development of new products. Macroscopic porous-media equations require constitutive relations, which account for the physical processes occurring at the micro-scale, to predict liquid transport at the macro-scale. In this study, micro-scale simulations were conducted using conventional computational fluid dynamics (CFD) technique (finite-volume method) to determine the macroscopic constitutive relations. The first part of this thesis deals with the single-phase flow in fibrous media, following which multi-phase flow through fibrous media was studied. Darcy permeability is an important parameter that characterizes creeping flow through a fibrous porous medium. It has a complex dependence on the medium's properties such as fibers' in-plane and through-plane orientation, diameter, aspect ratio, curvature, and porosity. A suite of 3D virtual fibrous structures with a wide range of geometric properties were constructed, and the permeability values of the structures were calculated by solving the 3D incompressible Navier-Stokes equations. The through-plane permeability was found to be a function of only the fiber diameter, the fibers' through-plane orientation, and the porosity of the medium. The numerical results were used to extend a permeability-porosity relation, developed in literature for 3D isotropic fibrous media, to a wide range of fibers' through-plane orientations. In applications where rate of capillary penetration is important, characterization of porous media usually involves determination of either the effective pore radius from capillary penetration experiments or a representative pore radius (R50) from pore-size distribution data. The relationship between effective and representative pore radii was studied by performing direct simulations of capillary penetration of a wetting liquid using a finite-volume-based volume-of-fluid (VOF) method. The simulated unidirectional liquid penetration through fibrous media followed Lucas-Washburn kinetics (L ˜ t1/2), except during the initial stages, which are dominated by inertial forces. Even though fluid properties and contact angle were kept constant in the simulations, the effective pore radii were found to be quite different from the representative radii. It can be concluded that the differences between effective and representative pore radii did not arise from contact angle variations. The unsaturated flow through fibrous media at the macro-scale is typically described using Richard's equation which requires constitutive relations: capillary pressure and permeability as a function of liquid saturation. In the present study, the quasi-static capillary pressure-saturation (P c-S) relationship for the primary drainage in a 3D isotropic fibrous medium was determined by performing micro-scale simulations using a VOF method. The Pc-S relationship obtained from the VOF method was compared with the results from the full-morphology (FM) method. Good agreement was observed between the results from the VOF and FM methods, thus suggesting that the FM method, a computationally less intensive method as compared to VOF method, may be sufficient for estimating the Pc-S relationship for primary drainage.

The Structural Basis of IKs Ion-Channel Activation: Mechanistic Insights from Molecular Simulations.

PubMed

Ramasubramanian, Smiruthi; Rudy, Yoram

2018-06-05

Relating ion channel (iCh) structural dynamics to physiological function remains a challenge. Current experimental and computational techniques have limited ability to explore this relationship in atomistic detail over physiological timescales. A framework associating iCh structure to function is necessary for elucidating normal and disease mechanisms. We formulated a modeling schema that overcomes the limitations of current methods through applications of artificial intelligence machine learning. Using this approach, we studied molecular processes that underlie human IKs voltage-mediated gating. IKs malfunction underlies many debilitating and life-threatening diseases. Molecular components of IKs that underlie its electrophysiological function include KCNQ1 (a pore-forming tetramer) and KCNE1 (an auxiliary subunit). Simulations, using the IKs structure-function model, reproduced experimentally recorded saturation of gating-charge displacement at positive membrane voltages, two-step voltage sensor (VS) movement shown by fluorescence, iCh gating statistics, and current-voltage relationship. Mechanistic insights include the following: 1) pore energy profile determines iCh subconductance; 2) the entire protein structure, not limited to the pore, contributes to pore energy and channel subconductance; 3) interactions with KCNE1 result in two distinct VS movements, causing gating-charge saturation at positive membrane voltages and current activation delay; and 4) flexible coupling between VS and pore permits pore opening at lower VS positions, resulting in sequential gating. The new modeling approach is applicable to atomistic scale studies of other proteins on timescales of physiological function. Copyright © 2018 Biophysical Society. Published by Elsevier Inc. All rights reserved.

Investigation of thin/well-tunable liquid/gas diffusion layers exhibiting superior multifunctional performance in low-temperature electrolytic water splitting

DOE PAGES

Kang, Zhenye; Mo, Jingke; Yang, Gaoqiang; ...

2016-10-11

Liquid/gas diffusion layers (LGDLs), which are located between the catalyst layer (CL) and bipolar plate (BP), play an important role in enhancing the performance of water splitting in proton exchange membrane electrolyzer cells (PEMECs). They are expected to transport electrons, heat, and reactants/products simultaneously with minimum voltage, current, thermal, interfacial, and fluidic losses. Here in this study, the thin titanium-based LGDLs with straight-through pores and well-defined pore morphologies are comprehensively investigated for the first time. The novel LGDL with a 400 μm pore size and 0.7 porosity achieved a best-ever performance of 1.66 V at 2 A cm -2 andmore » 80 °C, as compared to the published literature. The thin/well-tunable titanium based LGDLs remarkably reduce ohmic and activation losses, and it was found that porosity has a more significant impact on performance than pore size. In addition, an appropriate equivalent electrical circuit model has been established to quantify the effects of pore morphologies. The rapid electrochemical reaction phenomena at the center of the PEMEC are observed by coupling with high-speed and micro-scale visualization systems. Lastly, the observed reactions contribute reasonable and pioneering data that elucidate the effects of porosity and pore size on the PEMEC performance. This study can be a new guide for future research and development towards high-efficiency and low-cost hydrogen energy.« less

Observations of the Dynamic Connectivity of the Non-Wetting Phase During Steady State Flow at the Pore Scale Using 3D X-ray Microtomography

NASA Astrophysics Data System (ADS)

Reynolds, C. A.; Menke, H. P.; Blunt, M. J.; Krevor, S. C.

2015-12-01

We observe a new type of non-wetting phase flow using time-resolved pore scale imaging. The traditional conceptual model of drainage involves a non-wetting phase invading a porous medium saturated with a wetting phase as either a fixed, connected flow path through the centres of pores or as discrete ganglia which move individually through the pore space, depending on the capillary number. We observe a new type of flow behaviour at low capillary number in which the flow of the non-wetting phase occurs through networks of persistent ganglia that occupy the large pores but continuously rearrange their connectivity (Figure 1). Disconnections and reconnections occur randomly to provide short-lived pseudo-steady state flow paths between pores. This process is distinctly different to the notion of flowing ganglia which coalesce and break-up. The size distribution of ganglia is dependent on capillary number. Experiments were performed by co-injecting N2and 25 wt% KI brine into a Bentheimer sandstone core (4mm diameter, 35mm length) at 50°C and 10 MPa. Drainage was performed at three flow rates (0.04, 0.3 and 1 ml/min) at a constant fractional flow of 0.5 and the variation in ganglia populations and connectivity observed. We obtained images of the pore space during steady state flow with a time resolution of 43 s over 1-2 hours. Experiments were performed at the Diamond Light Source synchrotron. Figure 1. The position of N2 in the pore space during steady state flow is summed over 40 time steps. White indicates that N2 occupies the space over >38 time steps and red <5 time steps.

Neutrons measure phase behavior in pores at Angstrom size

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bardoel, Agatha A; Melnichenko, Yuri B

Researchers have measured the phase behavior of green house gases in pores at the Angstrom-level, using small angle neutron scattering (SANS) at the Oak Ridge National Laboratory's High Flux Isotope Reactor. Yuri Melnichenko, an instrument scientist on the General Purpose Small Angle Neutron Scattering (GP SANS) Diffractometer at ORNL's High Flux Isotope Reactor, his postdoctoral associate Lilin He and collaborators Nidia Gallego and Cristian Contescu from the Material Sciences Division (ORNL) were engaged in the work. They were studying nanoporous carbons to assess their attractiveness as storage media for hydrogen, with a view to potential use for on-board hydrogen storagemore » for transportation applications. Nanoporous carbons can also serve as electrode material for supercapacitors and batteries. The researchers successfully determined that the most efficiently condensing pore size in a carbon nanoporous material for hydrogen storage is less than one nanometer. In a paper recently published by the Journal of the American Chemical Society, the collaborators used small angle neutron scattering to study how hydrogen condenses in small pores at ambient temperature. They discovered that the surface-molecule interactions create internal pressures in pores that may exceed the external gas pressure by a factor of up to 50. 'This is an exciting result,' Melnichenko said, 'as you achieve extreme densification in pores 'for free', i.e. without spending any energy. These results can be used to guide the development of new carbon adsorbents tailored to maximize hydrogen storage capacities.' Another important factor that defines the adsorption capacity of sub-nanometer pores is their shape. In order to get accurate structural information and maximize sorption capacity, it is important that pores are small and of approximately uniform size. In collaboration with Drexel University's Yury Gogotsi who supplied the samples, Melnichenko and his collaborators used the GP SANS instrument to study how the size and shape of pores in sub-nanometer porous carbons varies, depending on the manufacturing conditions. While small angle X-ray scattering (SAXS) can do the job too, Melnichenko says, the SANS method broke new ground in analyzing the shape and behavior of pores at subnanometer size, when subjected to varying synthesis temperature. 'We found that these very small pores are in fact spherical, and that when we change the synthesis conditions, they become elongated, even 'slit-like', and all of this on a subnanometer scale,' Melnichenko said.« less

Quantification of Organic Porosity and Water Accessibility in Marcellus Shale Using Neutron Scattering

DOE PAGES

Gu, Xin; Mildner, David F. R.; Cole, David R.; ...

2016-04-28

Pores within organic matter (OM) are a significant contributor to the total pore system in gas shales. These pores contribute most of the storage capacity in gas shales. Here we present a novel approach to characterize the OM pore structure (including the porosity, specific surface area, pore size distribution, and water accessibility) in Marcellus shale. By using ultrasmall and small-angle neutron scattering, and by exploiting the contrast matching of the shale matrix with suitable mixtures of deuterated and protonated water, both total and water-accessible porosity were measured on centimeter-sized samples from two boreholes from the nanometer to micrometer scale withmore » good statistical coverage. Samples were also measured after combustion at 450 °C. Analysis of scattering data from these procedures allowed quantification of OM porosity and water accessibility. OM hosts 24–47% of the total porosity for both organic-rich and -poor samples. This porosity occupies as much as 29% of the OM volume. In contrast to the current paradigm in the literature that OM porosity is organophilic and therefore not likely to contain water, our results demonstrate that OM pores with widths >20 nm exhibit the characteristics of water accessibility. In conclusion, our approach reveals the complex structure and wetting behavior of the OM porosity at scales that are hard to interrogate using other techniques.« less

Quantification of Organic Porosity and Water Accessibility in Marcellus Shale Using Neutron Scattering

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gu, Xin; Mildner, David F. R.; Cole, David R.

Pores within organic matter (OM) are a significant contributor to the total pore system in gas shales. These pores contribute most of the storage capacity in gas shales. Here we present a novel approach to characterize the OM pore structure (including the porosity, specific surface area, pore size distribution, and water accessibility) in Marcellus shale. By using ultrasmall and small-angle neutron scattering, and by exploiting the contrast matching of the shale matrix with suitable mixtures of deuterated and protonated water, both total and water-accessible porosity were measured on centimeter-sized samples from two boreholes from the nanometer to micrometer scale withmore » good statistical coverage. Samples were also measured after combustion at 450 °C. Analysis of scattering data from these procedures allowed quantification of OM porosity and water accessibility. OM hosts 24–47% of the total porosity for both organic-rich and -poor samples. This porosity occupies as much as 29% of the OM volume. In contrast to the current paradigm in the literature that OM porosity is organophilic and therefore not likely to contain water, our results demonstrate that OM pores with widths >20 nm exhibit the characteristics of water accessibility. In conclusion, our approach reveals the complex structure and wetting behavior of the OM porosity at scales that are hard to interrogate using other techniques.« less

Reactive multiphase flow at the pore-scale: the melting of a crystalline framework during the injection of buoyant hot volatiles

NASA Astrophysics Data System (ADS)

Andrea, P.; Huber, C.; Bachmann, O.; Chopard, B.

2010-12-01

Multiphase reactive flows occur naturally in various environments in the shallow subsurface, e.g. CO2 injections in saturated reservoirs, exsolved methane flux in shallow sediments and H20-CO2 volatiles in magmatic systems. Because of their multiphase nature together with the nonlinear feedbacks between reactions (dissolution/melting or precipitation) and the flow field at the pore-scale, the study of these dynamical processes remains a great challenge. In this study we focus on the injection of buoyant hot volatiles exsolved from a magmatic intrusion underplating a crystal-rich magma (porous medium). We use some simple theoretical models and a pore-scale multiphase reactive lattice Boltzmann model to investigate how the heat carried by the volatile phase affects the evolution of the porous medium spatially and temporally. We find that when the reaction rate is relatively slow and when the injection rate of volatiles is large (high injection Capillary number), the dissolution of the porous medium can be described by a local Peclet number (ratio of advective to diffusive flux of heat/reactant in the main gas channel). When the injection rate of volatile is reduced, or when the reaction rate is large, the dynamics transition to more complex regimes, where subvertical gas channels are no longer stable and can break into disconnected gas slugs. For the case of the injection of hot volatiles in crystal-rich magmatic systems, we find that the excess enthalpy advected by buoyant volatiles penetrates the porous medium over distances ~r Pe, where r is the average radius of the volatile channel (~pore size). The transport of heat by buoyant gases through a crystal mush is therefore in most cases limited to distances < meters. Our results also suggest that buoyant volatiles can carry chemical species (Li,F, Cl) far into a mush as their corresponding local Peclet number is several orders of magnitude greater than that for heat, owing to their low diffusion coefficients.

Non-scaling behavior of electroosmotic flow in voltage-gated nanopores

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lian, Cheng; Gallegos, Alejandro; Liu, Honglai

2017-01-01

Ionic size effects and electrostatic correlations result in the non-monotonic dependence of the electrical conductivity on the pore size. For ion transport at a high gating voltage, the conductivity oscillates with the pore size due to a significant overlap of the electric double layers.

Nano-Pore Size Analysis by SAXS Method of Cementitious Mortars Undergoing Delayed Ettringite Formation

NASA Astrophysics Data System (ADS)

Shekar, Yamini

This research investigates the nano-scale pore structure of cementitious mortars undergoing delayed ettringite formation (DEF) using small angle x-ray scattering (SAXS). DEF has been known to cause expansion and cracking during later ages (around 4000 days) in concrete that has been heat cured at temperatures of 70°C or above. Though DEF normally occurs in heat cured concrete, mass cured concrete can also experience DEF. Large crystalline pressures result in smaller pore sizes. The objectives of this research are: (1) to investigate why some samples expand early than later expansion, (2) to evaluate the effects of curing conditions and pore size distributions at high temperatures, and (3) to assess the evolution of the pore size distributions over time. The most important outcome of the research is the pore sizes obtained from SAXS were used in the development of a 3-stage model. From the data obtained, the pore sizes increase in stage 1 due to initial ettringite formation and in turn filling up the smallest pores. Once the critical pore size threshold is reached (around 20nm) stage 2 is formed due to cracking which tends to decrease in the pore sizes. Finally, in stage 3, the cracking continues, therefore increasing in the pore size.

Pore-scale mechanisms of gas flow in tight sand reservoirs

DOE Office of Scientific and Technical Information (OSTI.GOV)

Silin, D.; Kneafsey, T.J.; Ajo-Franklin, J.B.

2010-11-30

Tight gas sands are unconventional hydrocarbon energy resource storing large volume of natural gas. Microscopy and 3D imaging of reservoir samples at different scales and resolutions provide insights into the coaredo not significantly smaller in size than conventional sandstones, the extremely dense grain packing makes the pore space tortuous, and the porosity is small. In some cases the inter-granular void space is presented by micron-scale slits, whose geometry requires imaging at submicron resolutions. Maximal Inscribed Spheres computations simulate different scenarios of capillary-equilibrium two-phase fluid displacement. For tight sands, the simulations predict an unusually low wetting fluid saturation threshold, at whichmore » the non-wetting phase becomes disconnected. Flow simulations in combination with Maximal Inscribed Spheres computations evaluate relative permeability curves. The computations show that at the threshold saturation, when the nonwetting fluid becomes disconnected, the flow of both fluids is practically blocked. The nonwetting phase is immobile due to the disconnectedness, while the permeability to the wetting phase remains essentially equal to zero due to the pore space geometry. This observation explains the Permeability Jail, which was defined earlier by others. The gas is trapped by capillarity, and the brine is immobile due to the dynamic effects. At the same time, in drainage, simulations predict that the mobility of at least one of the fluids is greater than zero at all saturations. A pore-scale model of gas condensate dropout predicts the rate to be proportional to the scalar product of the fluid velocity and pressure gradient. The narrowest constriction in the flow path is subject to the highest rate of condensation. The pore-scale model naturally upscales to the Panfilov's Darcy-scale model, which implies that the condensate dropout rate is proportional to the pressure gradient squared. Pressure gradient is the greatest near the matrix-fracture interface. The distinctive two-phase flow properties of tight sand imply that a small amount of gas condensate can seriously affect the recovery rate by blocking gas flow. Dry gas injection, pressure maintenance, or heating can help to preserve the mobility of gas phase. A small amount of water can increase the mobility of gas condensate.« less

Mineral transformation controls speciation and pore-fluid transmission of contaminants in waste-weathered Hanford sediments

NASA Astrophysics Data System (ADS)

Perdrial, Nicolas; Thompson, Aaron; O'Day, Peggy A.; Steefel, Carl I.; Chorover, Jon

2014-09-01

Portions of the Hanford Site (WA, USA) vadose zone were subjected to weathering by caustic solutions during documented releases of high level radioactive waste (containing Sr, Cs and I) from leaking underground storage tanks. Previous studies have shown that waste-sediment interactions can promote variable incorporation of contaminants into neo-formed mineral products (including feldspathoids and zeolites), but processes regulating the subsequent contaminant release from these phases into infiltrating background pore waters remain poorly known. In this paper, reactive transport experiments were conducted with Hanford sediments previously weathered for one year in simulated hyper-alkaline waste solutions containing high or low 88Sr, 127I, and 133Cs concentrations, with or without CO2(aq). These waste-weathered sediments were leached in flow-through column experiments with simulated background pore water (characteristic of meteoric recharge) to measure contaminant release from solids formed during waste-sediment interaction. Contaminant sorption-desorption kinetics and mineral transformation reactions were both monitored using continuous-flow and wet-dry cycling regimes for ca. 300 pore volumes. Less than 20% of contaminant 133Cs and 88Sr mass and less than 40% 127I mass were released over the course of the experiment. To elucidate molecular processes limiting contaminant release, reacted sediments were studied with micro- (TEM and XRD) and molecular- (Sr K-edge EXAFS) scale methods. Contaminant dynamics in column experiments were principally controlled by rapid dissolution of labile solids and competitive exchange reactions. In initially feldspathoidic systems, time-dependent changes in the local zeolitic bonding environment observed with X-ray diffraction and EXAFS are responsible for limiting contaminant release. Linear combination fits and shell-by-shell analysis of Sr K-edge EXAFS data revealed modification in Sr-Si/Al distances within the zeolite cage. Wet-dry cycling did not affect significantly molecular-scale transformations relative to continuous-flow controls. Results indicate that contaminants bound to the solid phase in distinct micro- and molecular-scale coordinative environments can generate similar macro-scale release behaviors, highlighting the need for multi-scale interrogations to constrain mechanisms of reactive transport. Data also indicate that weathering-induced change in ion exchange selectivity coefficients should be incorporated in simulations of contaminant release from caustic high-level radioactive waste impacted sediments.

Initial characterization of mudstone nanoporosity with small angle neutron scattering using caprocks from carbon sequestration sites.

DOE Office of Scientific and Technical Information (OSTI.GOV)

McCray, John; Navarre-Sitchler, Alexis; Mouzakis, Katherine

Geological carbon sequestration relies on the principle that CO{sub 2} injected deep into the subsurface is unable to leak to the atmosphere. Structural trapping by a relatively impermeable caprock (often mudstone such as a shale) is the main trapping mechanism that is currently relied on for the first hundreds of years. Many of the pores of the caprock are of micrometer to nanometer scale. However, the distribution, geometry and volume of porosity at these scales are poorly characterized. Differences in pore shape and size can cause variation in capillary properties and fluid transport resulting in fluid pathways with different capillarymore » entry pressures in the same sample. Prediction of pore network properties for distinct geologic environments would result in significant advancement in our ability to model subsurface fluid flow. Specifically, prediction of fluid flow through caprocks of geologic CO{sub 2} sequestration reservoirs is a critical step in evaluating the risk of leakage to overlying aquifers. The micro- and nanoporosity was analyzed in four mudstones using small angle neutron scattering (SANS). These mudstones are caprocks of formations that are currently under study or being used for carbon sequestration projects and include the Marine Tuscaloosa Group, the Lower Tuscaloosa Group, the upper and lower shale members of the Kirtland Formation, and the Pennsylvanian Gothic shale. Total organic carbon varies from <0.3% to 4% by weight. Expandable clay contents range from 10% to {approx}40% in the Gothic shale and Kirtland Formation, respectively. Neutrons effectively scatter from interfaces between materials with differing scattering length density (i.e. minerals and pores). The intensity of scattered neutrons, I(Q), where Q is the scattering vector, gives information about the volume of pores and their arrangement in the sample. The slope of the scattering data when plotted as log I(Q) vs. log Q provides information about the fractality or geometry of the pore network. Results from this study, combined with high-resolution TEM imaging, provide insight into the differences in volume and geometry of porosity between these various mudstones.« less

Longitudinally Controlled Modification of Cylindrical and Conical Track-Etched Poly(ethylene terephthalate) Pores Using an Electrochemically Assisted Click Reaction

DOE PAGES

Coceancigh, Herman; Tran-Ba, Khanh-Hoa; Siepser, Natasha; ...

2017-09-27

Here in this study, the longitudinally controlled modification of the inner surfaces of poly(ethylene terephthalate) (PET) track-etched pores was explored using an electrochemically assisted Cu(I)-catalyzed azide–alkyne cycloaddition (CuAAC) click reaction. Cylindrical or conical PET track-etched pores were first decorated with ethynyl groups via the amidation of surface -COOH groups, filled with a solution containing Cu(II) and azide-tagged fluorescent dye, and then sandwiched between comb-shaped and planar gold electrodes. Cu(I) was produced at the comb-shaped working electrode by the reduction of Cu(II); it diffused along the pores toward the other electrode and catalyzed CuAAC between an azide-tagged fluorescent dye and amore » pore-tethered ethynyl group. The modification efficiency of cylindrical pores (ca. 1 μm in diameter) was assessed from planar and cross-sectional fluorescence microscope images of modified membranes. Planar images showed that pore modification took place only above the teeth of the comb-shaped electrode with a higher reaction yield for longer Cu(II) reduction times. Cross-sectional images revealed micrometer-scale gradient modification along the pore axis, which reflected a Cu(I) concentration profile within the pores, as supported by finite-element computer simulations. The reported approach was applicable to the asymmetric modification of cylindrical pores with two different fluorescent dyes in the opposite directions and also for the selective visualization of the tip and base openings of conical pores (ca. 3.5 μm in base diameter and ca. 1 μm in tip diameter). Lastly, the method based on electrochemically assisted CuAAC provides a controlled means to fabricate asymmetrically modified nanoporous membranes and, in the future, will be applicable for chemical separations and the development of sequential catalytic reactors.« less

Longitudinally Controlled Modification of Cylindrical and Conical Track-Etched Poly(ethylene terephthalate) Pores Using an Electrochemically Assisted Click Reaction

DOE Office of Scientific and Technical Information (OSTI.GOV)

Coceancigh, Herman; Tran-Ba, Khanh-Hoa; Siepser, Natasha

Here in this study, the longitudinally controlled modification of the inner surfaces of poly(ethylene terephthalate) (PET) track-etched pores was explored using an electrochemically assisted Cu(I)-catalyzed azide–alkyne cycloaddition (CuAAC) click reaction. Cylindrical or conical PET track-etched pores were first decorated with ethynyl groups via the amidation of surface -COOH groups, filled with a solution containing Cu(II) and azide-tagged fluorescent dye, and then sandwiched between comb-shaped and planar gold electrodes. Cu(I) was produced at the comb-shaped working electrode by the reduction of Cu(II); it diffused along the pores toward the other electrode and catalyzed CuAAC between an azide-tagged fluorescent dye and amore » pore-tethered ethynyl group. The modification efficiency of cylindrical pores (ca. 1 μm in diameter) was assessed from planar and cross-sectional fluorescence microscope images of modified membranes. Planar images showed that pore modification took place only above the teeth of the comb-shaped electrode with a higher reaction yield for longer Cu(II) reduction times. Cross-sectional images revealed micrometer-scale gradient modification along the pore axis, which reflected a Cu(I) concentration profile within the pores, as supported by finite-element computer simulations. The reported approach was applicable to the asymmetric modification of cylindrical pores with two different fluorescent dyes in the opposite directions and also for the selective visualization of the tip and base openings of conical pores (ca. 3.5 μm in base diameter and ca. 1 μm in tip diameter). Lastly, the method based on electrochemically assisted CuAAC provides a controlled means to fabricate asymmetrically modified nanoporous membranes and, in the future, will be applicable for chemical separations and the development of sequential catalytic reactors.« less

Porous medium acoustics of wave-induced vorticity diffusion

NASA Astrophysics Data System (ADS)

Müller, T. M.; Sahay, P. N.

2011-02-01

A theory for attenuation and dispersion of elastic waves due to wave-induced generation of vorticity at pore-scale heterogeneities in a macroscopically homogeneous porous medium is developed. The diffusive part of the vorticity field associated with a viscous wave in the pore space—the so-called slow shear wave—is linked to the porous medium acoustics through incorporation of the fluid strain rate tensor of a Newtonian fluid in the poroelastic constitutive relations. The method of statistical smoothing is then used to derive dynamic-equivalent elastic wave velocities accounting for the conversion scattering process into the diffusive slow shear wave in the presence of randomly distributed pore-scale heterogeneities. The result is a simple model for wave attenuation and dispersion associated with the transition from viscosity- to inertia-dominated flow regime.

Evaluation of accessible mineral surface areas for improved prediction of mineral reaction rates in porous media

NASA Astrophysics Data System (ADS)

Beckingham, Lauren E.; Steefel, Carl I.; Swift, Alexander M.; Voltolini, Marco; Yang, Li; Anovitz, Lawrence M.; Sheets, Julia M.; Cole, David R.; Kneafsey, Timothy J.; Mitnick, Elizabeth H.; Zhang, Shuo; Landrot, Gautier; Ajo-Franklin, Jonathan B.; DePaolo, Donald J.; Mito, Saeko; Xue, Ziqiu

2017-05-01

The rates of mineral dissolution reactions in porous media are difficult to predict, in part because of a lack of understanding of mineral reactive surface area in natural porous media. Common estimates of mineral reactive surface area used in reactive transport models for porous media are typically ad hoc and often based on average grain size, increased to account for surface roughness or decreased by several orders of magnitude to account for reduced surface reactivity of field as opposed to laboratory samples. In this study, accessible mineral surface areas are determined for a sample from the reservoir formation at the Nagaoka pilot CO2 injection site (Japan) using a multi-scale image analysis based on synchrotron X-ray microCT, SEM QEMSCAN, XRD, SANS, and FIB-SEM. This analysis not only accounts for accessibility of mineral surfaces to macro-pores, but also accessibility through connected micro-pores in smectite, the most abundant clay mineral in this sample. While the imaging analysis reveals that most of the micro- and macro-pores are well connected, some pore regions are unconnected and thus inaccessible to fluid flow and diffusion. To evaluate whether mineral accessible surface area accurately reflects reactive surface area a flow-through core experiment is performed and modeled at the continuum scale. The core experiment is performed under conditions replicating the pilot site and the evolution of effluent solutes in the aqueous phase is tracked. Various reactive surface area models are evaluated for their ability to capture the observed effluent chemistry, beginning with parameter values determined as a best fit to a disaggregated sediment experiment (Beckingham et al., 2016) described previously. Simulations that assume that all mineral surfaces are accessible (as in the disaggregated sediment experiment) over-predict the observed mineral reaction rates, suggesting that a reduction of RSA by a factor of 10-20 is required to match the core flood experimental data. While the fit of the effluent chemistry (and inferred mineral dissolution rates) greatly improve when the pore-accessible mineral surface areas are used, it was also necessary to include highly reactive glass phases to match the experimental observations, in agreement with conclusions from the disaggregated sediment experiment. It is hypothesized here that the 10-20 reduction in reactive surface areas based on the limited pore accessibility of reactive phases in core flood experiment may be reasonable for poorly sorted and cemented sediments like those at the Nagaoka site, although this reflects pore rather than larger scale heterogeneity.

Induced groundwater flux by increases in the aquifer's total stress.

PubMed

Chang, Ching-Min; Yeh, Hund-Der

2015-01-01

Fluid-filled granular soils experience changes in total stress because of earth and oceanic tides, earthquakes, erosion, sedimentation, and changes in atmospheric pressure. The pore volume may deform in response to the changes in stress and this may lead to changes in pore fluid pressure. The transient fluid flow can therefore be induced by the gradient in excess pressure in a fluid-saturated porous medium. This work demonstrates the use of stochastic methodology in prediction of induced one-dimensional field-scale groundwater flow through a heterogeneous aquifer. A closed-form of mean groundwater flux is developed to quantify the induced field-scale mean behavior of groundwater flow and analyze the impacts of the spatial correlation length scale of log hydraulic conductivity and the pore compressibility. The findings provided here could be useful for the rational planning and management of groundwater resources in aquifers that contain lenses with large vertical aquifer matrix compressibility values. © 2014, National Ground Water Association.

Changes in Pore Water Quality After Peatland Restoration: Assessment of a Large-Scale, Replicated Before-After-Control-Impact Study in Finland

NASA Astrophysics Data System (ADS)

Menberu, Meseret Walle; Marttila, Hannu; Tahvanainen, Teemu; Kotiaho, Janne S.; Hokkanen, Reijo; Kløve, Bjørn; Ronkanen, Anna-Kaisa

2017-10-01

Drainage is known to affect peatland natural hydrology and water quality, but peatland restoration is considered to ameliorate peatland degradation. Using a replicated BACIPS (Before-After-Control-Impact Paired Series) design, we investigated 24 peatlands, all drained for forestry and subsequently restored, and 19 pristine control boreal peatlands with high temporal and spatial resolution data on hydroclimate and pore water quality. In drained conditions, total nitrogen (Ntot), total phosphorus (Ptot), and dissolved organic carbon (DOC) in pore water were several-fold higher than observed at pristine control sites, highlighting the impacts of long-term drainage on pore water quality. In general, pore water DOC and Ntot decreased after restoration measures but still remained significantly higher than at pristine control sites, indicating long time lags in restoration effects. Different peatland classes and trophic levels (vegetation gradient) responded differently to restoration, primarily due to altered hydrology and varying acidity levels. Sites that were hydrologically overrestored (inundated) showed higher Ptot, Ntot, and DOC than well-restored or insufficiently restored sites, indicating the need to optimize natural-like hydrological regimes when restoring peatlands drained for forestry. Rich fens (median pH 6.2-6.6) showed lower pore water Ptot, Ntot, and DOC than intermediate and poor peats (pH 4.0-4.6) both before and after restoration. Nutrients and DOC in pore water increased in the first year postrestoration but decreased thereafter. The most important variables related to pore water quality were trophic level, peatland class, water table level, and soil and air temperature.

Parametric study of thin film evaporation from nanoporous membranes

NASA Astrophysics Data System (ADS)

Wilke, Kyle L.; Barabadi, Banafsheh; Lu, Zhengmao; Zhang, TieJun; Wang, Evelyn N.

2017-10-01

The performance and lifetime of advanced electronics are often dictated by the ability to dissipate heat generated within the device. Thin film evaporation from nanoporous membranes is a promising thermal management approach, which reduces the thermal transport distance across the liquid film while also providing passive capillary pumping of liquid to the evaporating interface. In this work, we investigated the dependence of thin film evaporation from nanoporous membranes on a variety of geometric parameters. Anodic aluminum oxide membranes were used as experimental templates, where pore radii of 28-75 nm, porosities of 0.1-0.35, and meniscus locations down to 1 μm within the pore were tested. We demonstrated different heat transfer regimes and observed more than an order of magnitude increase in dissipated heat flux by operating in the pore-level evaporation regime. The pore diameter had little effect on pore-level evaporation performance due to the negligible conduction resistance from the pore wall to the evaporating interface. The dissipated heat flux scaled with porosity as the evaporative area increased. Furthermore, moving the meniscus as little as 1 μm into the pore decreased the dissipated heat flux by more than a factor of two due to the added resistance to vapor escaping the pore. The experimental results elucidate thin film evaporation from nanopores and confirm findings of recent modeling efforts. This work also provides guidance for the design of future thin film evaporation devices for advanced thermal management. Furthermore, evaporation from nanopores is relevant to water purification, chemical separations, microfluidics, and natural processes such as transpiration.

X-Ray Micro-CT Observations of Hydrate Pore Habit and Lattice Boltzmann Simulations on Permeability Evolution in Hydrate Bearing Sediments (HBS)

NASA Astrophysics Data System (ADS)

Chen, X.; Espinoza, N.; Verma, R.; Prodanovic, M.

2017-12-01

We use X-ray micro-computed tomography (μCT) to observe xenon hydrate growth. During xenon hydrate formation in a single pore and a sandpack, we observe heterogeneous (patchy) hydrate distribution at both pore (10 μm) and core scales (10 cm). These results present similarities with earlier observations on naturally occurring and synthetic hydrate-bearing sediment (HBS). Based on image analyses of xenon hydrate in the single pore, we find that, under the quasi-isothermal condition, the xenon volumetric growth rate versus overpressurization curve fits an Arrhenius type equation. Using the μCT images of HBS, we are able to calculate the permeability of HBS using a lattice Boltzmann method. We find the reduced permeability versus hydrate saturation curve fits a simple Corey-type model as suggested by earlier studies. However, patchy distribution of hydrate does not permit a straightforward interpretation of the saturation exponent. This work provides fundamental observations of hydrate growth and pore habit in sediments and how hydrate habit affects the hydraulic conductivity of HBS. Further implications can be extended to the strength, seismic velocities and electrical properties of HBS.

Pore-scale simulations of drainage in granular materials: Finite size effects and the representative elementary volume

NASA Astrophysics Data System (ADS)

Yuan, Chao; Chareyre, Bruno; Darve, Félix

2016-09-01

A pore-scale model is introduced for two-phase flow in dense packings of polydisperse spheres. The model is developed as a component of a more general hydromechanical coupling framework based on the discrete element method, which will be elaborated in future papers and will apply to various processes of interest in soil science, in geomechanics and in oil and gas production. Here the emphasis is on the generation of a network of pores mapping the void space between spherical grains, and the definition of local criteria governing the primary drainage process. The pore space is decomposed by Regular Triangulation, from which a set of pores connected by throats are identified. A local entry capillary pressure is evaluated for each throat, based on the balance of capillary pressure and surface tension at equilibrium. The model reflects the possible entrapment of disconnected patches of the receding wetting phase. It is validated by a comparison with drainage experiments. In the last part of the paper, a series of simulations are reported to illustrate size and boundary effects, key questions when studying small samples made of spherical particles be it in simulations or experiments. Repeated tests on samples of different sizes give evolution of water content which are not only scattered but also strongly biased for small sample sizes. More than 20,000 spheres are needed to reduce the bias on saturation below 0.02. Additional statistics are generated by subsampling a large sample of 64,000 spheres. They suggest that the minimal sampling volume for evaluating saturation is one hundred times greater that the sampling volume needed for measuring porosity with the same accuracy. This requirement in terms of sample size induces a need for efficient computer codes. The method described herein has a low algorithmic complexity in order to satisfy this requirement. It will be well suited to further developments toward coupled flow-deformation problems in which evolution of the microstructure require frequent updates of the pore network.

Annealing effect on thermodynamic and physical properties of mesoporous silicon: A simulation and nitrogen sorption study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kumar, Pushpendra, E-mail: pkumar-iitd@yahoo.com; Huber, Patrick, E-mail: patrick.huber@tuhh.de

Discovery of porous silicon formation in silicon substrate in 1956 while electro-polishing crystalline Si in hydrofluoric acid (HF), has triggered large scale investigations of porous silicon formation and their changes in physical and chemical properties with thermal and chemical treatment. A nitrogen sorption study is used to investigate the effect of thermal annealing on electrochemically etched mesoporous silicon (PS). The PS was thermally annealed from 200°C to 800°C for 1 hr in the presence of air. It was shown that the pore diameter and porosity of PS vary with annealing temperature. The experimentally obtained adsorption / desorption isotherms show hysteresis typicalmore » for capillary condensation in porous materials. A simulation study based on Saam and Cole model was performed and compared with experimentally observed sorption isotherms to study the physics behind of hysteresis formation. We discuss the shape of the hysteresis loops in the framework of the morphology of the layers. The different behavior of adsorption and desorption of nitrogen in PS with pore diameter was discussed in terms of concave menisci formation inside the pore space, which was shown to related with the induced pressure in varying the pore diameter from 7.2 nm to 3.4 nm.« less

Characterization of Biogenic Gas and Mineral Formation Process by Denitrification in Porous Media

NASA Astrophysics Data System (ADS)

Hall, C. A.; Kim, D.; Mahabadi, N.; van Paassen, L. A.

2017-12-01

Biologically mediated processes have been regarded and developed as an alternative approach to traditional ground improvement techniques. Denitrification has been investigated as a potential ground improvement process towards liquefaction hazard mitigation. During denitrification, microorganisms reduce nitrate to dinitrogen gas and facilitate calcium carbonate precipitation as a by-product under adequate environmental conditions. The formation of dinitrogen gas desaturates soils and allows for potential pore pressure dampening during earthquake events. While, precipitation of calcium carbonate can improve the mechanical properties by filling the voids and cementing soil particles. As a result of small changes in gas and mineral phases, the mechanical properties of soils can be significantly affected. Prior research has primarily focused on quantitative analysis of overall residual calcium carbonate mineral and biogenic gas products in lab-scale porous media. However, the distribution of these products at the pore-scale has not been well-investigated. In this research, denitrification is activated in a microfluidic chip simulating a homogenous pore structure. The denitrification process is monitored by sequential image capture, where gas and mineral phase changes are evaluated by image processing. Analysis of these images correspond with previous findings, which demonstrate that biogenic gas behaviour at the pore scale is affected by the balance between reaction, diffusion, and convection rates.

Mechanical instability and percolation of deformable particles through porous networks

NASA Astrophysics Data System (ADS)

Benet, Eduard; Lostec, Guillaume; Pellegrino, John; Vernerey, Franck

2018-04-01

The transport of micron-sized particles such as bacteria, cells, or synthetic lipid vesicles through porous spaces is a process relevant to drug delivery, separation systems, or sensors, to cite a few examples. Often, the motion of these particles depends on their ability to squeeze through small constrictions, making their capacity to deform an important factor for their permeation. However, it is still unclear how the mechanical behavior of these particles affects collective transport through porous networks. To address this issue, we present a method to reconcile the pore-scale mechanics of the particles with the Darcy scale to understand the motion of a deformable particle through a porous network. We first show that particle transport is governed by a mechanical instability occurring at the pore scale, which leads to a binary permeation response on each pore. Then, using the principles of directed bond percolation, we are able to link this microscopic behavior to the probability of permeating through a random porous network. We show that this instability, together with network uniformity, are key to understanding the nonlinear permeation of particles at a given pressure gradient. The results are then summarized by a phase diagram that predicts three distinct permeation regimes based on particle properties and the randomness of the pore network.

Nanometer-scale imaging and pore-scale fluid flow modeling inchalk

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tomutsa, Liviu; Silin, Dmitriy; Radmilovich, Velimir

2005-08-23

For many rocks of high economic interest such as chalk,diatomite, tight gas sands or coal, nanometer scale resolution is neededto resolve the 3D-pore structure, which controls the flow and trapping offluids in the rocks. Such resolutions cannot be achieved with existingtomographic technologies. A new 3D imaging method, based on serialsectioning and using the Focused Ion Beam (FIB) technology has beendeveloped. FIB allows for the milling of layers as thin as 10 nanometersby using accelerated Ga+ ions to sputter atoms from the sample surface.After each milling step, as a new surface is exposed, a 2D image of thissurface is generated. Next,more » the 2D images are stacked to reconstruct the3D pore or grain structure. Resolutions as high as 10 nm are achievableusing this technique. A new image processing method uses directmorphological analysis of the pore space to characterize thepetrophysical properties of diverse formations. In addition to estimationof the petrophysical properties (porosity, permeability, relativepermeability and capillary pressures), the method is used for simulationof fluid displacement processes, such as those encountered in variousimproved oil recovery (IOR) approaches. Computed with the new methodcapillary pressure curves are in good agreement with laboratory data. Themethod has also been applied for visualization of the fluid distributionat various saturations from the new FIB data.« less

Mesoporous Polymer Frameworks from End-Reactive Bottlebrush Copolymers

DOE PAGES

Altay, Esra; Nykypanchuk, Dmytro; Rzayev, Javid

2017-08-07

Reticulated nanoporous materials generated by versatile molecular framework approaches are limited to pore dimensions on the scale of the utilized rigid molecular building blocks (<5 nm). The inherent flexibility of linear polymers precludes their utilization as long framework connectors for the extension of this strategy to larger length scales. We report a method for the fabrication of mesoporous frameworks by using bottlebrush copolymers with reactive end blocks serving as rigid macromolecular interconnectors with directional reactivity. End-reactive bottlebrush copolymers with pendant alkene functionalities were synthesized by a combination of controlled radical polymerization and polymer modification protocols. Ru-catalyzed cross-metathesis cross-linking of bottlebrushmore » copolymers with two reactive end blocks resulted in the formation of polymer frameworks where isolated cross-linked domains were interconnected with bottlebrush copolymer bridges. The resulting materials were characterized by a continuous network pore structure with average pore sizes of 9–50 nm, conveniently tunable by the length of the utilized bottlebrush copolymer building blocks. As a result, the materials fabrication strategy described in this work expands the length scale of molecular framework materials and provides access to mesoporous polymers with a molecularly tunable reticulated pore structure without the need for templating, sacrificial component etching, or supercritical fluid drying.« less

Solute mixing regulates heterogeneity of mineral precipitation in porous media: Effect of Solute Mixing on Precipitation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cil, Mehmet B.; Xie, Minwei; Packman, Aaron I.

Synchrotron X-ray microtomography was used to track the spatiotemporal evolution of mineral precipitation and the consequent alteration of the pore structure. Column experiments were conducted by injecting CaCl2 and NaHCO3 solutions into granular porous media either as a premixed supersaturated solution (external mixing) or as separate solutions that mixed within the specimen (internal mixing). The two mixing modes produced distinct mineral growth patterns. While internal mixing promoted transverse heterogeneity with precipitation at the mixing zone, external mixing favored relatively homogeneous precipitation along the flow direction. The impact of precipitation on pore water flow and permeability was assessed via 3-D flowmore » simulations, which indicated anisotropic permeability evolution for both mixing modes. Under both mixing modes, precipitation decreased the median pore size and increased the skewness of the pore size distribution. Such similar pore-scale evolution patterns suggest that the clogging of individual pores depends primarily on local supersaturation state and pore geometry.« less

Relationship between chemical structure of soil organic matter and intra-aggregate pore structure: evidence from X-ray computed micro-tomography

NASA Astrophysics Data System (ADS)

Kravchenko, Alexandra; Grandy, Stuart A.

2014-05-01

Understanding chemical structure of soil organic matter (SOM) and factors that affect it are vital for gaining understanding of mechanisms of C sequestration by soil. Physical protection of C by adsorption to mineral particles and physical disconnection between C sources and microbial decomposers is now regarded as the key component of soil C sequestration. Both of the processes are greatly influenced by micro-scale structure and distribution of soil pores. However, because SOM chemical structure is typically studied in disturbed (ground and sieved) soil samples the experimental evidence of the relationships between soil pore structure and chemical structure of SOM are still scarce. Our study takes advantage of the X-ray computed micro-tomography (µ-CT) tools that enable non-destructive analysis of pore structure in intact soil samples. The objective of this study is to examine the relationship between SOM chemical structure and pore-characteristics in intact soil macro-aggregates from two contrasting long-term land uses. The two studied land use treatments are a conventionally tilled corn-soybean-wheat rotation treatment and a native succession vegetation treatment removed from agricultural use >20 years ago. The study is located in southwest Michigan, USA, on sandy-loam Typic Hapludalfs. For this study we used soil macro-aggregates 4-6 mm in size collected at 0-15 cm depth. The aggregate size was selected so as both to enable high resolution of µ-CT and to provide sufficient amount of soil for C measurements. X-ray µ-CT scanning was conducted at APS Argonne at a scanning resolution of 14 µm. Two scanned aggregates (1 per treatment) were used in this preliminary study. Each aggregate was cut into 7 "geo-referenced" sections. Analyses of pore characteristics in each section were conducted using 3DMA and ImageJ image analysis tools. SOM chemistry was analyzed using pyrolysis/gas chromatography-mass spectroscopy. Results demonstrated that the relationships between SOM chemical structure and pore characteristics differed in the aggregates of the two treatments. For example, in the agricultural treatment, the aggregate sections with prevalence of small pores had lower relative lignin abundance, while higher lignin abundances occurred in aggregate sections with more large pores. This relationship could be reflecting the low accessibility of the sections dominated by small pores to plant roots. It is interesting to note that no relationship between pores and lignin were observed in the aggregate from the native succession treatment. In the native succession aggregate we found that a larger presence of protein and N-bearing compounds was associated with sections with greater presence of 35-90 µm pores. This could be a result of fungal activities, as pores of this size constitute a primary fungal habitat and fungi are known for secreting proteins. Fewer fungi in the soil under agricultural management are likely the reason that no such relationship was observed in the aggregate from the agricultural treatment. Our preliminary results indicate that substantial spatial variability patterns in SOM chemical structure can exist even within a single macro-aggregate and that pores are likely a main driver of intra-aggregate SOM chemistry.

Fractal Dimensionality of Pore and Grain Volume of a Siliciclastic Marine Sand

NASA Astrophysics Data System (ADS)

Reed, A. H.; Pandey, R. B.; Lavoie, D. L.

Three-dimensional (3D) spatial distributions of pore and grain volumes were determined from high-resolution computer tomography (CT) images of resin-impregnated marine sands. Using a linear gradient extrapolation method, cubic three-dimensional samples were constructed from two-dimensional CT images. Image porosity (0.37) was found to be consistent with the estimate of porosity by water weight loss technique (0.36). Scaling of the pore volume (Vp) with the linear size (L), V~LD provides the fractal dimensionalities of the pore volume (D=2.74+/-0.02) and grain volume (D=2.90+/-0.02) typical for sedimentary materials.

Structure of assemblies of metal nanowires in mesoporous alumina membranes studied by EXAFS, XANES, X-ray diffraction and SAXS.

PubMed

Benfield, Robert E; Grandjean, Didier; Dore, John C; Esfahanian, Hamid; Wu, Zhonghua; Kröll, Michael; Geerkens, Marcus; Schmid, Günter

2004-01-01

Mesoporous alumina membranes ("anodic aluminium oxide", or "AAO") are made by anodic oxidation of aluminium metal. These membranes contain hexagonal arrays of parallel non-intersecting cylindrical pores perpendicular to the membrane surface. By varying the anodisation voltage, the pore diameters are controllable within the range 5-250 nm. We have used AAO membranes as templates for the electrochemical deposition of metals within the pores to produce nanowires. These represent assemblies of one-dimensional quantum wires with prospective applications in electronic, optoelectronic and magnetic devices. Detailed characterisation of the structures of these nanowire assemblies on a variety of length scales is essential to understand their physical properties and evaluate their possible applications. We have used EXAFS, XANES, WAXS, high energy X-ray diffraction and SAXS to study their structure and bonding. In this paper we report the results of our studies of four different nanowire systems supported in AAO membranes. These are the ferromagnetic metals iron and cobalt, the superconducting metal tin, and the semiconductor gallium nitride. Iron nanowires in pores of diameter over the range 12 nm-72 nm are structurally very similar to bcc bulk iron. They have a strong preferred orientation within the alumina pores. Their XANES shows significant differences from that of bulk iron, showing that the electronic structure of the iron nanowires depends systematically on their diameter. Cobalt nanowires are composed of a mixture of hcp and fcc phases, but the ratio of the two phases does not depend in a simple way on the pore diameter or preparation conditions. In bulk cobalt, the fcc beta-phase is normally stable only at high temperatures. Strong preferred orientation of the c-axis in the pores was found. Tin nanowires in alumina membranes with pores diameters between 12 nm and 72 nm have a tetragonal beta-structure at ambient temperature and also at 80 K. Magnetic susceptibility measurements show that they are diamagnetic, and become superconducting at the same temperature as bulk tin (3.7 K). Gallium nitride nanowires have been prepared in alumina membranes with pore diameter 24 nm by a novel method. Gallium nitrate was deposited in the pores from aqueous solution and thermolysed at 1000 degrees C to form Ga2O3, which was reacted with ammonia at 1000 degrees C. The GaN nanowires have the wurtzite structure. Preparation at 1150 degrees C led to the incorporation of aluminium in the GaN. The mesoscopic ordering of the pores in the AAO membranes and their filling by metal nanowires has been studied by SAXS, which shows patterns of Bragg peaks arising from the pore arrays. Additionally, the cobalt nanowires have been the subject of an initial ASAXS study.

Clinical Assessment of a Novel Jasmonate Cosmeceutical, LR2412-Cx, for the Treatment of Skin Aging.

PubMed

Alexiades, Macrene

2016-02-01

The jasmonates are a novel class of plant-derived anti-aging compounds. Among these, LR2412-Cx (tetrahydrojasmonic acid, Visionnaire) has been demonstrated to reduce photoaging and the appearance of wrinkles, as well as to upregulate collagens, hyaluronic acid and fibrillin. To clinically study the cosmetic effects of a novel jasmonate complex LR2412-Cx in the treatment of visible skin aging. LR2412-Cx was evaluated in a 15-subject open-label prospective clinical trial for the treatment of fine wrinkle appearance, texture, and pores. Subjects were evaluated by an investigator at baseline, day 1, day 3, and week 6 with the Alexiades comprehensive grading scale of skin aging, and introducing a novel pore-grading scale and subject quality of life assessments. The mean (SEM) at baseline and at week 6 following twice-daily application were: for the appearance of wrinkles 2.91 (0.12) and 2.70 (0.10); for texture 2.91 (0.10) and 2.55 (0.10); and for pores 3.29 (0.08) and 2.46 (0.09), respectively. The differences in all 3 categories at all follow-up intervals were statistically significant (P<.005). The percentage improvement in investigator-assessed grades relative to baseline at day 1, day 3, and week 6 were: 2.3%, 4.9%, and 7.4% for the appearance of wrinkles, 5.7%, 9.4%, and 12.4% for texture, and 14.2%, 21.6% and 25.2% for pores, respectively. No significant untoward effects were reported. Visionnaire LR2412-Cx is a novel jasmonate-containing compound that is safe and effective for the cosmetic treatment of fine wrinkle appearance, texture, and pores of the facial skin.

A physically-based analytical model to describe effective excess charge for streaming potential generation in saturated porous media

NASA Astrophysics Data System (ADS)

Jougnot, D.; Guarracino, L.

2016-12-01

The self-potential (SP) method is considered by most researchers the only geophysical method that is directly sensitive to groundwater flow. One source of SP signals, the so-called streaming potential, results from the presence of an electrical double layer at the mineral-pore water interface. When water flows through the pore space, it gives rise to a streaming current and a resulting measurable electrical voltage. Different approaches have been proposed to predict streaming potentials in porous media. One approach is based on the excess charge which is effectively dragged in the medium by the water flow. Following a recent theoretical framework, we developed a physically-based analytical model to predict the effective excess charge in saturated porous media. In this study, the porous media is described by a bundle of capillary tubes with a fractal pore-size distribution. First, an analytical relationship is derived to determine the effective excess charge for a single capillary tube as a function of the pore water salinity. Then, this relationship is used to obtain both exact and approximated expressions for the effective excess charge at the Representative Elementary Volume (REV) scale. The resulting analytical relationship allows the determination of the effective excess charge as a function of pore water salinity, fractal dimension and hydraulic parameters like porosity and permeability, which are also obtained at the REV scale. This new model has been successfully tested against data from the literature of different sources. One of the main finding of this study is that it provides a mechanistic explanation to the empirical dependence between the effective excess charge and the permeability that has been found by various researchers. The proposed petrophysical relationship also contributes to understand the role of porosity and water salinity on effective excess charge and will help to push further the use of streaming potential to monitor groundwater flow.

PolyA Single Strand DNA Translocation Through an Alpha-Hemolysin Pore Stem

NASA Technical Reports Server (NTRS)

OKeeffe, James; Cozmuta, Ioana; Stolc, Viktor

2003-01-01

A new model for the polymer-pore interaction energy is introduced, based on an atomic-scale description of coulombic polymer-pore interaction. The enhanced drift velocity, experimentally observed for short polymers, is successfully accounted for, using this interaction energy model. For R/R(sub 0)>4 (R(sub 0)=7 angstroms) the translocation velocity approaches the free space drift velocity v(sub 0). This motivates the need to appropriately derivatize artificial nanopores, where R>R(sub 0).

Experimental study and theoretical interpretation of saturation effect on ultrasonic velocity in tight sandstones under different pressure conditions

NASA Astrophysics Data System (ADS)

Li, Dongqing; Wei, Jianxin; Di, Bangrang; Ding, Pinbo; Huang, Shiqi; Shuai, Da

2018-03-01

Understanding the influence of lithology, porosity, permeability, pore structure, fluid content and fluid distribution on the elastic wave properties of porous rocks is of great significance for seismic exploration. However, unlike conventional sandstones, the petrophysical characteristics of tight sandstones are more complex and less understood. To address this problem, we measured ultrasonic velocity in partially saturated tight sandstones under different effective pressures. A new model is proposed, combining the Mavko-Jizba-Gurevich relations and the White model. The proposed model can satisfactorily simulate and explain the saturation dependence and pressure dependence of velocity in tight sandstones. Under low effective pressure, the relationship of P-wave velocity to saturation is pre-dominantly attributed to local (pore scale) fluid flow and inhomogeneous pore-fluid distribution (large scale). At higher effective pressure, local fluid flow gradually decreases, and P-wave velocity gradually shifts from uniform saturation towards patchy saturation. We also find that shear modulus is more sensitive to saturation at low effective pressures. The new model includes wetting ratio, an adjustable parameter that is closely related to the relationship between shear modulus and saturation.

Fish Gill Inspired Crossflow for Efficient and Continuous Collection of Spilled Oil.

PubMed

Dou, Yuhai; Tian, Dongliang; Sun, Ziqi; Liu, Qiannan; Zhang, Na; Kim, Jung Ho; Jiang, Lei; Dou, Shi Xue

2017-03-28

Developing an effective system to clean up large-scale oil spills is of great significance due to their contribution to severe environmental pollution and destruction. Superwetting membranes have been widely studied for oil/water separation. The separation, however, adopts a gravity-driven approach that is inefficient and discontinuous due to quick fouling of the membrane by oil. Herein, inspired by the crossflow filtration behavior in fish gills, we propose a crossflow approach via a hydrophilic, tilted gradient membrane for spilled oil collection. In crossflow collection, as the oil/water flows parallel to the hydrophilic membrane surface, water is gradually filtered through the pores, while oil is repelled, transported, and finally collected for storage. Owing to the selective gating behavior of the water-sealed gradient membrane, the large pores at the bottom with high water flux favor fast water filtration, while the small pores at the top with strong oil repellency allow easy oil transportation. In addition, the gradient membrane exhibits excellent antifouling properties due to the protection of the water layer. Therefore, this bioinspired crossflow approach enables highly efficient and continuous spilled oil collection, which is very promising for the cleanup of large-scale oil spills.

Position-Dependent Dynamics Explain Pore-Averaged Diffusion in Strongly Attractive Adsorptive Systems.

PubMed

Krekelberg, William P; Siderius, Daniel W; Shen, Vincent K; Truskett, Thomas M; Errington, Jeffrey R

2017-12-12

Using molecular simulations, we investigate the relationship between the pore-averaged and position-dependent self-diffusivity of a fluid adsorbed in a strongly attractive pore as a function of loading. Previous work (Krekelberg, W. P.; Siderius, D. W.; Shen, V. K.; Truskett, T. M.; Errington, J. R. Connection between thermodynamics and dynamics of simple fluids in highly attractive pores. Langmuir 2013, 29, 14527-14535, doi: 10.1021/la4037327) established that pore-averaged self-diffusivity in the multilayer adsorption regime, where the fluid exhibits a dense film at the pore surface and a lower density interior pore region, is nearly constant as a function of loading. Here we show that this puzzling behavior can be understood in terms of how loading affects the fraction of particles that reside in the film and interior pore regions as well as their distinct dynamics. Specifically, the insensitivity of pore-averaged diffusivity to loading arises from the approximate cancellation of two factors: an increase in the fraction of particles in the higher diffusivity interior pore region with loading and a corresponding decrease in the particle diffusivity in that region. We also find that the position-dependent self-diffusivities scale with the position-dependent density. We present a model for predicting the pore-average self-diffusivity based on the position-dependent self-diffusivity, which captures the unusual characteristics of pore-averaged self-diffusivity in strongly attractive pores over several orders of magnitude.

Multi-Scale Investigation of the Formation and Breakdown of Passive Films on Carbon Steel Rebar in Concrete

NASA Astrophysics Data System (ADS)

Ghods, Pouria

The multi-scale investigation presented in this thesis was carried out to understand better the mechanisms of passivation and chloride-induced depassivation of carbon steel reinforcement in concrete. The study consisted of electrochemical experiments (electrochemical impedance spectroscopy, linear polarization resistance, free corrosion potential, anodic polarization), microscopic examinations (scanning electron microscopy, transmission electron microscopy, selected area diffraction, convergent beam electron diffraction), numerical modeling (finite element method), and spectroscopic studies (x-ray photoelectron, energy dispersed x-ray, electron energy loss). Electrochemical and microscopic studies showed that the composition of the pore solution and the surface conditions of the rebar affect the passivity and depassivation of carbon steel in concrete. It was demonstrated that crevices between mill scale and steel may become potential sites for depassivation and pit nucleation. The numerical investigation that was carried out to test this hypothesis confirmed that the ratio of chloride to hydroxide concentrations, Cl-/OH-, in crevices increased to levels higher than that of the bulk pore solution, making crevices more vulnerable to depassivation. Therefore, it was concluded that the variability associated with reported chloride thresholds might be attributed, at least in part, to the variability in mill scale properties resulting from the variability in manufacturing. The nano-scale microscopic and spectroscopic studies indicated the formation of 4-10 nm-thick passive oxide films on carbon steel in simulated concrete pore solutions, and these films consisted of two layers separated with an indistinct border. The inner layer was mainly composed of protective Fe2+-rich oxides that are in epitaxial relationship with the underlying steel surface; while the outer layer mostly consisted of (possibly porous) Fe3+-rich oxides, through which chlorides can penetrate. It was proposed that, in the presence of chlorides, Fe+2-rich oxides in the inner layer transform into Fe+3-rich oxides and potentially become un-protective. Although how this transformation occurs is still subject of future research, there are evidences showing that the process most likely leads to the formation of local anodic and cathodic sites on the steel surface.

Pore-scale dynamics of salt transport in drying porous media

NASA Astrophysics Data System (ADS)

Shokri, N.

2013-12-01

Understanding the physics of water evaporation from saline porous media is important in many hydrological processes such as land-atmosphere interactions, water management, vegetation, soil salinity, and mineral-fluid interactions. We applied synchrotron x-ray micro-tomography to investigate the pore-scale dynamics of dissolved salt distribution in a three dimensional drying saline porous media using a cylindrical plastic column (15 mm in height and 8 mm in diameter) packed with sand particles saturated with CaI2 solution (5% concentration by mass) with a spatial and temporal resolution of 12 microns and 30 min, respectively. Every time the drying sand column was set to be imaged, two different images were recorded using distinct synchrotron X-rays energies immediately above (33.2690 keV) and below (33.0690 keV) the K-edge value of Iodine (33.1694 keV). Taking the difference between pixel gray values enabled us to delineate the spatial and temporal distribution of CaI2 concentration at pore scale. The experiment was continued for 12 hours. Results indicate that during early stages of evaporation, air preferentially invades large pores at the surface while finer pores remain saturated and connected to the wet zone at bottom via capillary-induced liquid flow. Consequently, the salt concentration increases preferentially in finer pores where evaporation occurs. The Peclet number (describing the competition between convection and diffusion) was greater than one in our experiment resulting in higher salt concentrations closer to the evaporation surface indicating a convection-driven process. The obtained salt profiles were used to evaluate the numerical solution of the convection-diffusion equation (CDE). Results show that the macro-scale CDE could capture the overall trend of the measured salt profiles but fail to produce the exact slope of the profiles. Our results shed new insight on the physics of salt transport and its complex dynamics in drying porous media and establish synchrotron x-ray micro-tomography as an effective tool to investigate the dynamics of dissolved salt transport in porous media with high spatial and temporal resolutions.

Modeling of viscoelastic properties of nonpermeable porous rocks saturated with highly viscous fluid at seismic frequencies at the core scale

NASA Astrophysics Data System (ADS)

Wang, Zizhen; Schmitt, Douglas R.; Wang, Ruihe

2017-08-01

A core scale modeling method for viscoelastic properties of rocks saturated with viscous fluid at low frequencies is developed based on the stress-strain method. The elastic moduli dispersion of viscous fluid is described by the Maxwell's spring-dash pot model. Based on this modeling method, we numerically test the effects of frequency, fluid viscosity, porosity, pore size, and pore aspect ratio on the storage moduli and the stress-strain phase lag of saturated rocks. And we also compared the modeling results to the Hashin-Shtrikman bounds and the coherent potential approximation (CPA). The dynamic moduli calculated from the modeling are lower than the predictions of CPA, and both of these fall between the Hashin-Shtrikman bounds. The modeling results indicate that the frequency and the fluid viscosity have similar effects on the dynamic moduli dispersion of fully saturated rocks. We observed the Debye peak in the phase lag variation with the change of frequency and viscosity. The pore structure parameters, such as porosity, pore size, and aspect ratio affect the rock frame stiffness and result in different viscoelastic behaviors of the saturated rocks. The stress-strain phase lags are larger with smaller stiffness contrasts between the rock frame and the pore fluid. The viscoelastic properties of saturated rocks are more sensitive to aspect ratio compared to other pore structure parameters. The results suggest that significant seismic dispersion (at about 50-200 Hz) might be expected for both compressional and shear waves passing through rocks saturated with highly viscous fluids.