Properties Of Porous Media Research Articles

Reactive Transport Modeling with a Coupled OpenFOAM®-PHREEQC Platform

Reactive transport modeling has established itself as a key player to analyze sophisticated hydro-geochemical interactions that occur over spatiotemporal scales on par with subsurface applications. In this paper, we benchmarked a new reactive transport package—porousMedia4Foam at the continuum scale considering complex and well-established cases available in the reactive transport modeling community. porousMedia4Foam was born by the successful coupling of two open-source packages—OpenFOAM® and PHREEQC. The flow governing equations, transport of species and the evolution of porous media properties are handled by OpenFOAM®, whereas the geochemistry is exclusively handled by PHREEQC. We further demonstrated the capability of using porousMedia4Foam to investigate reactive transport processes considering unstructured meshes. As porousMedia4Foam is an open-source package with included benefits to account for reactive transport processes occurring at various scales—pore, hybrid, and Darcy scales, we believe that porousMedia4Foam opens a new dimension to analyze reactive transport physics for various intriguing subsurface applications.

Effect of gravity on colloidal particle transport in a saturated porous medium: Analytical solutions and experiments.

The colloidal particle transport process in all porous media from laboratory to nature is affected by gravity. In this paper, a mathematical model of colloidal particle migration in a saturated porous medium with the gravity effect is established by combining the gap velocity (advection) with the settling velocity (gravity effect), and an analytical solution of the particle migration problem with time variation of the particle injection intensity is obtained using an integral transformation. The correctness and rationality of the analytical solution are verified by comparing the experimental and theoretical results of the particle migration problem in the point-source transient injection mode. The analytical solution can easily analyze the colloid transport experimental data in a variety of seepage directions. Analysis of the influence of seepage velocities in three different seepage directions on particle transport parameters shows: under the same seepage direction, the peak value of the breakthrough curve increased with an increase in the seepage velocity. The dispersion, adsorption coefficient, and deposition rate decreased with an increase in the seepage velocity. Under the same seepage velocity, the peak value of the breakthrough curve from large to small was vertically downward (VD)> horizontal (H)> vertically upward (VU), the order of dispersion from large to small was vertically downward (VD)>horizontal (H) >vertically upward (VU), the order of the adsorption coefficient and deposition rate of particles from large to small was vertically upward (VU)> horizontal (H) >vertically downward (VD), and the smaller the seepage velocity, the greater the relative differences in the peak value of the breakthrough curve, dispersion, the particle adsorption coefficient, and the deposition rate in the different seepage directions. Therefore, gravity is an important mechanism of particle migration in saturated porous media. The larger the particle size and density were, the smaller the seepage velocity was and the more obvious the effect of gravity. The findings of this study can help for better understanding of colloidal transport properties in porous media under the coupled effects of gravity and hydrodynamics.

A Dataset of 3D Structural and Simulated Transport Properties of Complex Porous Media

Physical processes that occur within porous materials have wide-ranging applications including - but not limited to - carbon sequestration, battery technology, membranes, oil and gas, geothermal energy, nuclear waste disposal, water resource management. The equations that describe these physical processes have been studied extensively; however, approximating them numerically requires immense computational resources due to the complex behavior that arises from the geometrically-intricate solid boundary conditions in porous materials. Here, we introduce a new dataset of unprecedented scale and breadth, DRP-372: a catalog of 3D geometries, simulation results, and structural properties of samples hosted on the Digital Rocks Portal. The dataset includes 1736 flow and electrical simulation results on 217 samples, which required more than 500 core years of computation. This data can be used for many purposes, such as constructing empirical models, validating new simulation codes, and developing machine learning algorithms that closely match the extensive purely-physical simulation. This article offers a detailed description of the contents of the dataset including the data collection, simulation schemes, and data validation.

Organic fluid migration in low permeability reservoirs restricted by pore structure parameters

The flow of fluids in porous media is a complex but essential study; due to the limitation of experimental methods, the research on ultra-low velocity flow of fluids has been developing slowly. This paper investigated the flow of oil in shale through laboratory tests to explore the flow characteristics of organic fluids at ultra-low velocities in ultra-low permeability porous media; the experimental results show that the flow of organic fluids in a specific porous medium at ultra-low velocity still follow Darcy's law, which is different from the previous research that believed that the ultra-low velocity flow of fluids must be non-Darcy flow. However, the flow characteristics of fluids are not static and will change with external conditions (Ambient temperature or Confining pressure). Moreover, an improved mathematical model of fluid flow based on Poiseuille's law is deduced, which can be verified well by the calculation and experimental data. The model comprehensively considers the shale stress sensitivity and the effects of the boundary layer on the fluid flow. The boundary layer is cleverly calculated through the concept of shale oil occurrence and confirmed with molecular dynamics simulation results. The correlation analysis between the critical parameters in the model and the geological parameters shows that any material composition of porous media has a specific influence on the fluid flow characteristics, especially the effect of clay minerals, that cannot be ignored. The analysis results show that when the relative content of clay minerals is about 50%, the porous medium has a better flow capacity; When the relative content of brittle minerals is between 70% and 80%, it has a better compressive ability. Simultaneously, the organic matter content index TOC has a specific inhibitory effect on fluid flow. Therefore, determining the properties of porous media and the changes in the external conditions of porous media is of great significance for engineering practice (e.g., the development of shale oil).

The Role of Pore‐Shape and Pore‐Space Heterogeneity in Non‐Archie Behavior of Resistivity Index Curves

AbstractResistivity index curves describe the relationship between electrical resistivity and water saturation of porous media and are critical in formation evaluation and for the geophysical monitoring of subsurface processes. Archie's second equation enforces a linear relationship between resistivity index and water saturation in log‐log plots which has been widely used for the assessment of in situ hydrocarbon saturation. However, resistivity index curves that deviate from Archie's equation are ubiquitous in subsurface reservoirs, especially complex carbonates exhibiting bimodal pore‐size distributions, where the effects of pore‐scale controlling factors on rock resistivity remain unclear. We implement pore‐network models built under controlled conditions of pore shapes, bimodal pore‐size distributions, pore connectivity, micropore fractions, and anisotropy to investigate the effects of pore shapes and pore‐space heterogeneity on resistivity index curves. Results indicate that percolating wetting films associated with pore shapes decrease the resistivity index at low values of water saturation and cause a decrease in saturation exponent. In cases of bimodal pore‐size distributions, micropore fractions control the connectivity between macropores, thus affecting water drainage and resistivity index curves. At low fractions of micropores, the resistivity index curve is governed by the connected macropore system at high values of water saturation and is then determined by micropores, thereby resulting in non‐Archie behavior. Pore‐size distributions and spatial anisotropy also affect the resistivity index curves. We summarize the observed pore‐space heterogeneity effects on resistivity index curves and compare model predictions to numerical simulations; both the geometric mean model and effective medium theory provide acceptable estimates of the electrical properties of bimodal porous media.

Review of Capillary Rise Experiments for Surface-Active Solutes in the Subsurface

Surface-active solutes that exist in the subsurface either naturally (humic acid) or as a result of anthropogenic activities (alcohols, surfactants, PFAS) alter the hydraulic and geotechnical properties of the unsaturated porous media. The alteration of properties is the result of concentration-dependent surface tension, and/or density, and the contact angle effects. These effects are manifested in the form of changes in water retention and conduction and changes in the suction component of the shear strength. Differences in the spatial distribution of these solutes in the subsurface result in capillary pressure gradients causing flow perturbations. Conceptual and numerical models to understand the effects of these solutes require concentration-dependent consideration of surface tension, density, and the contact angle effects on hydraulic and geotechnical properties of porous media. Capillary rise experiments have been carried out to either quantify the effect of surface-active solutes on the height of capillary rise or to determine the concentration-dependent contact angle changes due to salinity of the pore water. This paper provides a comprehensive review of the literature on capillary rise experiments and how they can potentially be used to characterize the hydraulic and geotechnical properties of unsaturated porous media affected by surface-active solutes.

Flow over embankment gabion weirs in free flow conditions

In this study, a series of laboratory tests were performed to investigate the effects of side ramp slope, crest length, and porous media properties on the flow regimes, water-surface profiles, discharge coefficients, and energy dissipation in embankment gabion weirs with upstream and downstream slopes. 24 physical models of solid and gabion weirs with three different upstream/downstream slopes (90°, 45° and 26.5°) were created. To investigate the complexity of flow over the porous-fluid interface and through the porous material, three-dimensional (3D) numerical simulations were developed. In numerical simulation, the standard k-ε turbulence model was utilized. A structured mesh domain was used to simulate the physical model. Water surface profiles above the porous weirs were used for comparison between the numerical simulations and measured data. These comparisons helped determine variables in the numerical simulations. Numerical simulation enables visualization of streamlines around and through the gabion weirs. In addition, mean stream wise velocity profiles above and within the porous structures were obtained. Numerical simulations showed that a reduction in the slope of the upstream face leads to an increased curvature of streamlines and the velocity distribution exhibits a non-uniform wavy shape due to the geometrical properties of the weirs. As the velocity profiles move downstream, the velocity distribution within the porous structures were more affected by the presence of the pores. The experimental results show that decreasing upstream slopes, from 90° to 26.5°, leads to decreased discharge coefficients. However, in all cases, gabion weirs lead to greater discharge coefficients than those of similar solid weirs. For milder side slopes, discharge ratios (flow passing through all faces of the gabion weirs over the inlet discharge) decreased nonlinearly. Moreover, with increasing the inlet discharge, relative energy dissipation was reduced up to 45% in gabion weirs.

Improved recurrent generative model for reconstructing large-size porous media from two-dimensional images.

Modeling the three-dimensional (3D) structure from a given 2D image is of great importance for analyzing and studying the physical properties of porous media. As an intractable inverse problem, many methods have been developed to address this fundamental problems over the past decades. Among many methods, the deep learning-(DL) based methods show great advantages in terms of accuracy, diversity, and efficiency. Usually, the 3D reconstruction from the 2D slice with a larger field-of-view is more conducive to simulate and analyze the physical properties of porous media accurately. However, due to the limitation of reconstruction ability, the reconstruction size of most widely used generative adversarial network-based model is constrained to 64^{3} or 128^{3}. Recently, a 3D porous media recurrent neural network based method (namely, 3D-PMRNN) (namely 3D-PMRNN) has been proposed to improve the reconstruction ability, and thus the reconstruction size is expanded to 256^{3}. Nevertheless, in order to train these models, the existed DL-based methods need to down-sample the original computed tomography (CT) image first so that the convolutional kernel can capture the morphological features of training images. Thus, the detailed information of the original CT image will be lost. Besides, the 3D reconstruction from a optical thin sectionis not available because of the large size of the cutting slice. In this paper, we proposed an improved recurrent generative model to further enhance the reconstruction ability (512^{3}). Benefiting from the RNN-based architecture, the proposed model requires only one 3D training sample at least and generates the 3D structures layer by layer. There are three more improvements: First, a hybrid receptive field for the kernel of convolutional neural network is adopted. Second, an attention-based module is merged into the proposed model. Finally, a useful sectionloss is proposed to enhance the continuity along the Z direction. Three experiments are carried out to verify the effectiveness of the proposed model. Experimental results indicate the good reconstruction ability of proposed model in terms of accuracy, diversity, and generalization. And the effectiveness of sectionloss is also proved from the perspective of visual inspection and statistical comparison.

Adjusting porous media properties to enhance the gas-phase OER for PEM water electrolysis in 3D simulations

A three-dimensional computational fluid dynamics study was employed to investigate the extent of the gas-phase contribution to the oxygen evolution reaction. The model was parametrized via comparison with experimental data. It was concluded from comparing non-isothermal and isothermal models that evaporation likely plays a key role in cell performance, along with heat generation. Porous transport layer (PTL) properties were adjusted in the model to compute the impact of such properties on cell performance. Current density increased as a result of reducing PTL permeability, increasing the liquid/gas interfacial area, and increasing porosity. Effects of the flow field plate were investigated as well. It was found that high in-plane permeability in the PTL may lead to redirection of flow in the channels, causing non-uniformity in anode conditions. Utilizing the insight from these investigations, the anode PTL properties were adjusted in an attempt to improve cell performance by regulating liquid water transport while maintaining uniformity. The simulation suggests that current can be increased by about 5–10% under constant operating conditions via changes in PTL properties.

3D MHD dusty nanofluid flow within cubic heterogeneous porous enclosures with hot and cold cylinders using non-homogeneous nanofluid model

The heterogeneity of the porous medium properties is an important topic due to the important wide practical applications in the reservoir rocks and the petroleum reservoirs. This study aims to examine both the heterogeneity of the permeability, thermal conductivity and the nanofluid model on the dusty nanofluid within a three-dimensional cubic container. The convective transport is due to the buoyancy–driven flow resulting from two inner hot/cold cylinders separated by variable distance [Formula: see text]. The nanofluids are simulated by a non-homogeneous two phase model and the impact of a constant magnetic field in Z -direction is considered. Two systems of the governing equations are introduced for the dusty and nanofluid phase and the boundary conditions for the nanoparticle function are passively controlled. The major findings revealed that the flow structures can be well-controlled using the distance between the inner cylinders. Also, the heterogeneity in [Formula: see text] plane gives a higher rate of the heat transfer. Furthermore, the maximizing of the dusty parameter is better for enhancing the dusty temperature and velocities.

Polymer induced permeability reduction: The influence of polymer retention and porous medium properties

Polymer injection is broadly applied for enhanced oil recovery (EOR) in high crude oil viscosity and heterogeneous reservoirs. Although polymer flooding is very effective to decrease the mobility ratio towards favorable values and improve sweep efficiency, some side effects have to be considered including the risk of a severe polymer induced permeability reduction (PIPR) resulting from polymer/rock interaction either near the wellbore of in-depth of the reservoir. Many factors affect the degree of PIPR such as rock mineralogy, oil saturation, temperature, formation water salinity, rock pore structure, polymer type, polymer molecular weight, shear rates in the porous medium, and quality of the injection water (solid particles and oil droplets content). Accurate assessment of PIPR is very important for polymer selection to define the relative merits of polymer flooding for a certain reservoir and avoid polymer injectivity loss during field operations. A severe PIPR can be due to excessive polymer retention inside the reservoir rock, fluid incompatibility of polymer with formation fluids and rocks, clogging of pore throats (accumulation of large polymer molecules at the pore throat), shear thickening due to high shear rate in the near-wellbore area, Improper preparation of the polymer solution, and bad quality of the injection brine used to prepare the polymer solution.In this paper, coreflooding as an assessment technique for PIPR is reviewed and a new interpretation technique is presented to correlated the polymer retention to permeability reduction measured from coreflooding experiments. Coupling the polymer retention and rock quality index was very effective in matching the permeability reduction for data presented in the literature for sandstone and carbonate rock samples.PIPR should be considered as an important design characteristic during any polymer selection workflow. Although different techniques are presented earlier, most of them lack the ability for upscaling. An accurate assessment of PIPR using experimental data permits critical evaluation of polymer flow deeper in the reservoir and prediction of any injectivity problems as well as improving project design.

Local Gas-Phase Current Contributions Influenced By Porous Media Properties and Geometric Features in PEM Electrolysis

To expand the commercialization of polymer electrolyte membrane water electrolysis (PEMWE) devices, it is beneficial to understand how cell geometry and porous media properties can impact cell performance. Due to the use of precious materials in PEMWE, particularly with an acidic membrane, it is cost-effective to simulate cell performance using a number of proposed designs to limit the number of prototypes. The use of three-dimensional (3-D) computational fluid dynamics (CFD) to simulate PEMWE 1 and alkaline 2 electrolysis operation has been previously demonstrated. This analysis sheds additional light on evaporation and the important role that it plays in facilitating the anodic and cathodic reactions.Evaporation rates in porous media vary immensely with changes in water content, which has been demonstrated experimentally. Zenyuk et al. 3 used computed tomography to quantify the liquid saturation and gas/liquid interfacial area inside a carbon gas diffusion layer. They linked these variables to evaporation rate using the injection feed pressure to adjust the liquid saturation. The authors determined that evaporation rates in fuel cells increase dramatically with a decrease in water content. Evaporation rate depends on the specific interfacial area (SIA). Measurements in porous media, namely sands and soils, have shown an increase in SIA with a decrease in liquid saturation. One may notice from Ouni et al. 4 that the SIA is indirectly proportional to liquid saturation when the maximum SIA is small and somewhat inversely proportional when the SIA is large. The nature of these relationships is considered in the present CFD model for evaporation in the porous transport layer (PTL) and catalyst layer.This study explores the effects of manifold geometry, flow field geometry, and properties such as PTL porosity, permeability, interfacial area, and anisotropy on local current density. Special emphasis is given to the contribution of the gas phase to the overall current and the conditions under which the gas-phase reaction is favorable. Changes in operating conditions, such as the feed temperature, feed rate, and cell potential, and how they impact local void fraction, relative humidity, and temperature at the anode are also investigated. The sensitivity of overall performance to material properties was found to be dependent on these operating conditions, primarily the anode inlet feed rate.References J. Lopata, Z. Kang, J. Young, G. Bender, J. W. Weidner, H-S. Cho, and S. Shimpalee, J. Electrochem. Soc., 168, 054518 (2021).J. S. Lopata, S-G. Kang, H-S. Cho, C-H. Kim, J. W. Weidner, S. Shimpalee, Electrochim. Acta, 390, 138802 (2021).I. V. Zenyuk, A. Lamibrac, J. Eller, D. Y. Parkinson, F. Marone, F. N. Büchi, and A. Weber, J. Phys. Chem. C, 120, 28701-28711 (2016).A. E. Ouni, B. Guo, H. Zhong, M. L. Brusseau, Chemosphere, 263, 128193 (2021). Figure 1

Entropy-based analysis and economic scrutiny of magneto thermal natural convection enhancement in a nanofluid-filled porous trapezium-shaped cavity having localized baffles

This article presents a modeling approach to predict the thermal natural convection inside a porous trapezium-shaped zone with baffles installed on the adiabatic side-walls. The cavity is filled with nanofluid and exposed under the effect of a magnetic field. The equations which govern the phenomenon have been solved numerically. For various configurations of the installed baffles, temperature field, the flow structure, heat exchange rate, and entropy production have been characterized for sundry figures of parameters i.e. Rayleigh (Ra), Hartmann (Ha), Darcy (Da), material’s porosity (ϵ), and nanoparticles’ concentration (ϕ). In addition, a cost–benefit analysis of the convection enhancement process within the system based on nanomaterials has been proposed. It has been ascertained that rising Ra, Da, and ϵ while lowering Ha improved the convective nanofluid flow. The influence of porous medium properties (material's porosity and permeability) on the convective flow intensity is more effective at moderate Ra. The average cooling rate increases with rising Ra, Da, and ϕ and declining Ha and ϵ. Moreover, obtained results characterize a positive economic feasibility of utilizing nanomaterials to improve thermal natural convection in the presence or absence of a magnetic field.

Simulation tool for the analysis of in-situ combustion experiments that considers complex kinetic schemes and detailed mass transfer- theoretical analysis of the gas phase CO oxidation reaction

A simulation tool was designed for analyzing various experimental setups that include the ability to model detailed chemical reaction schemes for in-situ combustion (ISC) analysis.,. The simulation tool was illustrated with a theoretical example to the extent of CO oxidation in a gaseous phase takes place during ISC. The models in the simulation tool are based on fundamental conservation laws, physical correlations for porous media properties, and property databases available in literature. Emphasis is made on the analysis of chemical reactions in the gas phase, a characteristic that may be useful when temperatures are above 700°C and oxygen, unburned hydrocarbons, and CO coexist. The three modules of the simulation tool: (i) Kinetic cell, (ii) One-dimensional reactor, and (iii) Combustion tube, can be used to represent in detail the processes taking place in the typical laboratory-scale equipment used to characterize ISC. Tools for the analysis of transport phenomena and multiphase reactions, present in all three models, can support the process of finding chemical kinetic parameters for an easier calculation of device-independent kinetic constants. Four applications have the simulator scope: (i) Analysis of reactions in the gas phase, (ii) Axial gradients in a kinetic cell, (iii) Pressure build-up in a combustion tube, and (iv) Ignition in a combustion tube. These examples highlight the importance that homogeneous reactions may have in these systems and the existence, under certain conditions, of concentration gradients that are normally neglected, and can affect the interpretation of ISC experiments.

Equation of state for confined fluids.

Fluids confined in small volumes behave differently than fluids in bulk systems. For bulk systems, a compact summary of the system's thermodynamic properties is provided by equations of state. However, there is currently a lack of successful methods to predict the thermodynamic properties of confined fluids by use of equations of state, since their thermodynamic state depends on additional parameters introduced by the enclosing surface. In this work, we present a consistent thermodynamic framework that represents an equation of state for pure, confined fluids. The total system is decomposed into a bulk phase in equilibrium with a surface phase. The equation of state is based on an existing, accurate description of the bulk fluid and uses Gibbs' framework for surface excess properties to consistently incorporate contributions from the surface. We apply the equation of state to a Lennard-Jones spline fluid confined by a spherical surface with a Weeks-Chandler-Andersen wall-potential. The pressure and internal energy predicted from the equation of state are in good agreement with the properties obtained directly from molecular dynamics simulations. We find that when the location of the dividing surface is chosen appropriately, the properties of highly curved surfaces can be predicted from those of a planar surface. The choice of the dividing surface affects the magnitude of the surface excess properties and its curvature dependence, but the properties of the total system remain unchanged. The framework can predict the properties of confined systems with a wide range of geometries, sizes, interparticle interactions, and wall-particle interactions, and it is independent of ensemble. A targeted area of use is the prediction of thermodynamic properties in porous media, for which a possible application of the framework is elaborated.

Use of the Dispersion Coefficient as the Sole Structural Parameter to Model Membrane Chromatography.

The characterization and modelling of membrane chromatography processes require the axial dispersion coefficient as a relevant and effective intrinsic property of porous media, instead of arbitrary assumptions on pore size distribution. The dispersion coefficient can be easily measured by experiments completely independent of chromatographic tests. The paper presents the prediction of experimentally obtained breakthrough curves using B14-TRZ-Epoxy2 membranes as a test case; the mathematical model implemented is based on the use of the experimentally measured axial dispersion coefficient as an input parameter. Application of the model and its comparison with the data demonstrate that alternative ways of explaining the shape of breakthrough curves, based on unverified assumptions about the membrane pore size distribution, are not feasible and not effectively supported by experimental evidence. In contrast, the axial dispersion coefficient is the only measurable parameter that accounts for all the different contributions to the dispersion phenomenon that occurs in the membrane chromatography process, including the effects due to porous structure and pore size distribution. Therefore, mathematical models that rely on the mere assumption of pore size distribution, regardless of the role of the axial dispersion coefficient, are in fact arbitrary and ultimately misleading.

Preparation of illite coated geomaterial microfluidic surfaces: Effect of salinity and heat treatment

Unique characteristics of clay (e.g., high surface area, deficiency in positive charges) make any clay abundant shales a good source of adsorbed gas. However, the presence of clay in porous media can also affect shale rock's producibility. The clay-water interaction can cause significant swelling and fines migration in the formation and impair the overall hydrocarbon recovery from shale.Geomaterial micromodels, developed by functionalizing traditional glass or PDMS surfaces with geomaterials (e.g., calcite, Quartz, clay), can represent the physicochemical properties of the natural porous media and have been used during the last few years to understand and evaluate the solid-fluid physicochemical interactions. This study focuses on developing a clay-coated geomaterial surface and investigates the effect of base fluid's salinity on clay adsorption to the glass surface. Glass capillary tubes and straight channel borosilicate glass micromodels are coated with Illite clay to represent the pore-scale clay chemistry of Caney Shale, a Mississippian unconventional play in Southern Oklahoma, USA. 10 wt% of Illite clay slurries made with brines of four different salinities are used to coat the glass-capillary tubes to understand the effect of salinity in clay adsorption on the glass surface and overall coating quality. To achieve a stable coating and evaluate the impact of heat treatment on coating's stability, straight channel glass flow cells coated with Illite clay are heat-treated at low (25 °C) and high temperature (125 °C), and the results are compared with an untreated coated surface. Flooding tests were carried out with brines of different salinities on the coated surface to evaluate the stability of the coating.The experimental results indicated a strong relationship between the brine's salinity and the adsorption of clay particles on the glass surface. An increase in brine concentration resulted in improved adsorption of clay particles on the glass surface. Experiments involving heat treating the glass surface following the coating demonstrated significant improvement in the stability of the coating.

Nano-scale Wetting Film Impact on Multiphase Transport Properties in Porous Media

Nano-scale Wetting Film Impact on Multiphase Transport Properties in Porous Media

Enhancement of thin-section image using super-resolution method with application to the mineral segmentation and classification in tight sandstone reservoir

The accurate characterization of rock and fluid properties in porous media of oil reservoir using thin sections depends on reliable segmentation and classification of the involved phases. However, in tight sandstone reservoirs, rock image segmentation and classification become a challenging task due to the limitation of resolution on representing the pores, throats, and other minerals at the microscale size. The resolution of an image has thus become a critical factor. Therefore, this study aims to use the super-resolution technique, which can enhance the image resolution by deep learning methods to overcome the limitation of original image resolution, and significantly improve the traditional segmentation and classification results. A Generative Adversarial Network (GAN)-based Super-resolution(SR) model was used as a pre-processing step to enhance the resolution of a given image. Then the effectiveness of super-resolution technique in post-processing procedures like segmentation and classification is evaluated using a tight sandstone data set from Ordos basin. The performance of segmentation with super-resolution enhancement is compared among Level set, Simple Linear Iterative Clustering (SLIC), and Watershed. As numerical test results reflect, segmentation in super-resolution image can achieve the segmentation of tiny minerals, pores, throats, and other blurry edges which can't be correctly segmented in the original image. Furthermore, in classification, we use a Convolutional Neural Network (CNN) model and a logistic regression model to demonstrate the advantage of SR enhancement. After the super-resolution process, the classification accuracy of CNN and logistic models have both improved for over 10%. The comparisons and analyses are presented to show that super-resolution could significantly improve these post-processing procedures. In addition, we discuss the potentials and limitations of applying super-resolution in segmentation and classification.

A three-dimension multi-scale fusion reconstruction method for porous media based on pattern-matching

Accurate three-dimensional modeling has an important influence on the evaluation and prediction of the physical properties of porous media. In view of the inherent natural structures, pores are multiscale in many porous media. As a result of the tradeoff between the field of view (FOV) and resolution, it is difficult to obtain high-resolution and large-scale images using single-resolution imaging equipment. Generally, low-resolution images with a large FOV lack detailed features, while the FOV of high-resolution images is too small to contain the information of the entire microstructure. Therefore, fusing images from different resolutions and scales to reconstruct models is an promising solution for addressing these issues. In this study, an improved method for reconstructing a high-resolution and large-scale model based on three-dimensional pattern matching is proposed. The algorithm can fuse two models from different resolutions and scales, in which the structures of large-scale pores in the low-resolution model are used as background and a high-resolution model is applied to build pattern sets to reconstruct fine-scale pores based on the background. The final result is a model containing large-scale and fine-scale pores. The accuracy and stability of the proposed method were tested by using two samples. From subjective and objective perspectives, through the comparisons of visual effects and statistical properties between generating models and target models, we found that the method can reconstruct accurate models.