Gas In Porous Media Research Articles

Pore-scale study of three-dimensional three-phase dynamic behaviors and displacement processes in porous media

Carbon dioxide geological sequestration is a key method to alleviate global warming and enhance oil recovery, where the three-phase displacement processes of oil, water, and carbon dioxide gas in porous media are frequently encountered. In this study, a three-phase three-dimensional lattice Boltzmann method coupled with special wettability and outlet boundary schemes is adopted to simulate the three-phase displacement processes in porous media. The method is validated by the contact angles on a curved surface and droplet flowing through the outlet boundary. With this method, the influences of capillary number, wettability, and local large pores on three-phase flow are investigated. In particular, different dynamic behaviors of fluids are observed at the pore scale, such as bypass-double displacement, stop-wait displacement, burst displacement, snap-off trapping, and corner flow. Further, Euler number and oil saturation are calculated to quantitatively characterize the fluidic morphology and displacement efficiency under different conditions. For all three phases, the Euler number of low capillary number, strong water-wet, and structures with large and medium pores is relatively low, indicating that the morphology of fluids is more connective. For enhancing oil recovery efficiency, high capillary number and strong water-wet structures are beneficial.

Research on Oil and Gas Adsorption Optimization Based on CFD Modeling and Process Simulation.

In the process of oil extraction and refining, some of the liquid light hydrocarbon components will inevitably evaporate into the atmosphere, causing serious air pollution and safety hazards. This paper is focused on oil and gas adsorption systems to comprehensively optimize key parameters by combining computational fluid dynamics (CFD) modeling with process simulation, enabling the efficient treatment of hazardous materials. First, a CFD model of the hydrocarbon adsorption process is established to the porous media model by a user-defined function (UDF). Subsequently, the mass transfer process of oil and gas in porous media is successfully simulated to obtain the gas distribution in an industrial fixed bed adsorption tower. The adsorption tank is intensified, and the gas distribution in the tank is improved by optimizing the height-to-diameter ratio of the equipment and the design of the intake distributor. Third, the cyclic two-tank adsorption model of the pressure swing adsorption (PSA) process is established for key parameters optimization. Finally, the operating parameters and conditions of the PSA process are suspected by considering five factors affecting the adsorption efficiency: adsorption time, adsorption pressure, adsorption temperature, feed flow rate, and purge ratio of the washing step.

Submodels of 2-d model of the motion of fluid or gas in a porous medium with an external non-stationary source or absorption

The motion of fluid or gas in a porous medium is the main object of investigation of underground hydromechanics. The model describing this motion was called “Porous medium”.In our paper, we study a general 2-d model of the motion of fluid or gas in porous medium with an external non-stationary source or absorption. As the main research method, we use the method of group (symmetry) analysis, which is one of the most effective ways to obtain information about the properties of solutions to differential equations that define a physical model. A group classification of the differential equation defining studied physical model is carried out. As a result, all basic models with different symmetry properties are obtained. For the basic model, which admits the widest group a classification of all its invariant submodels is performed and all invariant submodels, defined by invariant solutions of rank 1 are studied. All solutions found have physical meaning.The set of explicitly found solutions forms a 47-parametric family of exact solutions. Each solution in this family depends on an arbitrary function defining an external non-stationary source or absorption. For each solution, for the specific values of the parameters on which it depends and for this specific function, we obtained a graph of the pressure distribution.Other solutions are used to describe the movement of a liquid or gas if either the pressure and its rate of change, or the pressure and one of its gradient components, are given at an initial time at a fixed point. The set of these solutions depends on 13 parameters and a function defining an external non-stationary source or absorption. For specific values of this function and specific values of the parameters on which each solution depends, the existence and uniqueness of a solution to the corresponding boundary value problem under some additional conditions has been established. Each such problem is solved numerically. The results of these decisions we reflected in the graphs.The significance of obtained solutions lies in the fact that we have obtained a database consisting of two multiparameter families of invariant solutions of rank 1 of the equation describing the motion of fluid or gas in a porous medium in the presence of an external non-stationary source or absorption. Every solution depends on an empirically determined function. These solutions describe specific physical processes. They can also be used as test solutions in numerical calculations related to the study of the motion of fluid or gas in a porous medium during fluids filtering, engineering surveys in the construction of building structures and in the extraction of shale oil or gas.

Empirical and Numerical Modelling of Gas–Gas Diffusion for Binary Hydrogen–Methane Systems at Underground Gas Storage Conditions

The physical process in which a substance moves from a location with a higher concentration to a location with a lower concentration is known as molecular diffusion. It plays a crucial role during the mixing process between different gases in porous media. Due to the petrophysical properties of the porous medium, the diffusion process occurs slower than in bulk, and the overall process is also affected by thermodynamic conditions. The complexity of measuring gas–gas diffusion in porous media at increased pressure and temperature resulted in significant gaps in data availability for modelling this process. Therefore, correlations for ambient conditions and simplified diffusivity models have been used for modelling purposes. In this study, correlations in dependency of petrophysical and thermodynamic properties were developed based on more than 30 measurements of the molecular diffusion of the binary system hydrogen–methane in gas storage rock samples at typical subsurface conditions. It allows reproducing the laboratory observations by evaluating the bulk diffusion coefficient and the tortuosity factor with relative errors of less than 50 % with minor exceptions, leading to a strong improvement compared to existing correlations. The developed correlation was implemented in the open-source simulator DuMux and the implementation was validated by reproducing the measurement results. The validated implementation in DuMux allows to model scenarios such as Underground Hydrogen Storage (UHS) on a field-scale and, as a result, can be used to estimate the temporary loss of hydrogen into the cushion gas and the purity of withdrawn gas due to the gas–gas mixing process.

Combining wall interactions, fluid momentum balances and the Maxwell-Stefan equations for gas transport in porous media: An alternative approach

This paper presents a modelling framework for incorporating wall interactions into the Maxwell-Stefan equations for ideal gases in porous media. In contrast to already existing models in literature, such as the Dusty Gas, Binary Friction and Modified Binary Friction models, the framework makes use of N−1 (with N being the number of gas species) independent mass balances for the gas species in combination with a total fluid momentum balance. This approach has the advantage that already existing numerical schemes for fluid momentum balances, such as Darcy’s law or the Brinkman equations, can be used with only minor modifications. It also allows for separate initialisation of the velocity and pressure fields, something that is often beneficial when solving convection–diffusion equations numerically. The derived model is validated against both stationary and time-dependent experimental data from literature for binary Ar-He systems in porous media, using Knudsen diffusivities to define the wall friction terms.

Lattice Boltzmann Simulations of the Dynamic Adsorption of Gas in Porous Media: Effect of Grain Size Distribution

Lattice Boltzmann Simulations of the Dynamic Adsorption of Gas in Porous Media: Effect of Grain Size Distribution

Model reduction for molecular diffusion in nanoporous media

Porous materials are widely used for applications in gas storage and separation. The diffusive properties of a variety of gases in porous media can be modeled using molecular dynamics simulations that can be computationally demanding depending on the pore geometry, complexity, and amount of gas adsorbed. We explore a dimensionality reduction approach for estimating the self-diffusion coefficient of gases in simple pores using Langevin dynamics, such that the three-dimensional (3D) atomistic interactions that determine the diffusion properties of realistic systems can be reduced to an effective one-dimensional (1D) diffusion problem along the pore axis. We demonstrate the approach by modeling the transport of nitrogen molecules in single-walled carbon nanotubes of different radii, showing that 1D Langevin models can be parametrized with a few single-particle 3D atomistic simulations. The reduced 1D model predicts accurate diffusion coefficients over a broad range of temperatures and gas densities. Our work paves the way for studying the diffusion process of more general porous materials such as zeolites or metal-organics frameworks with effective models of reduced complexity.

Dissolution mass transfer of trapped gases in porous media: A correlation of Sherwood, Reynolds, and Schmidt numbers

The dissolution mass transfer of trapped phases in porous media is important in various fields, such as groundwater contamination, geological carbon sequestration, and geological energy storage. One of the difficulties in this study is the observation of the porous media interior during the dissolution mass transfer. Without the ability to monitor the process inside porous media, earlier studies were unable to measure the interfacial area of the trapped phase and thus were unable to calculate the mass transfer coefficient. In addition, complicating phenomena, such as two-stage dissolution and dissolution fingering, also affect the mass transfer process, in which it cannot be elucidated without observing to the porous media interior. In this present study, we investigated the dissolution mass transfer of various trapped phase in porous media at various fluid velocity by using micro-tomography. Therefore, the trapped phase interfacial area and mass transfer coefficient were successfully derived. In addition, the experimental setup was also designed to avoid the two-stage dissolution and dissolution fingering that could affect the mass transfer process significantly. As a result, we limit the observed phenomena to dissolution mass transfer processes alone. At the end, a mass transfer model based on Sherwood, Reynolds, and Schmidt numbers was developed. Because a mass transfer model that can be used for different trapped phases has never been developed, this developed model serves as an important reference for dissolution mass transfer model of trapped phases in porous media.

Developing interphase mass transfer correlations for non-aqueous phase liquid to gas in porous media with thermal enhancement

An in-depth understanding of interphase mass transfer from a non-aqueous phase liquid (NAPL) to a gas is crucial and indispensable for properly designing and optimizing remediation schemes in NAPL-contaminated sites involving thermal treatment. A series of polluted soil column venting experiments were conducted to thoroughly evaluate this nonequilibrium behavior at both the initial steady-state stage and transient stage of mass transfer. Two new correlations are proposed to predict the mass transfer efficiency and duration of the steady-state stage. Additionally, it is proposed the disparity of behavior in the transient stage is caused by different modes of interfacial area reduction, which are controlled by two competing phenomena: NAPL film spreading, and evaporation at the NAPL–gas interface. These processes are described by specific mathematical expressions. These findings provide deep insight into thermally enhanced NAPL–gas interfacial mass transfer and have the potential to be applied to modeling studies and field applications of multiphase extraction.

Characterization of dynamic adsorption regimes in synthetic and natural porous structures using lattice Boltzmann simulations

This paper presents the first systematic study on the characterization of dynamic adsorption regimes of gas in porous media using the ratio of inter- to intraparticle diffusion coefficients. The effect of the ratio between the two diffusion coefficients on the adsorption dynamics was investigated in combination with the adsorbent particles size and the disorder parameter, which numerically describes pore space heterogeneity, by mathematical modelling using the lattice Boltzmann simulations for fluid flow and the convective-diffusive transport of an adsorbate dissolved in a fluid. To characterize the dynamic adsorption regimes, for the first time, a relationship between the surface and total adsorption amount was used. The obtained results during simulations in two-dimensional synthetic porous structures showed that the size of the adsorbent particle strongly affects the surface and the total adsorption dynamics. An increase in the particle size promotes an increase in the rate of surface adsorption. Depending on the ratio of inter- to intraparticle diffusion coefficients, increasing particle size promotes either an acceleration or slowdown of the total adsorption dynamics. The results revealed in two-dimensional structures were verified by simulations in three-dimensional digital models of natural sandstones, which were obtained using X-ray computed tomography.

Foam-Assisted Capillary Trapping in Saline Aquifers—An Initial–Residual Saturation Analysis

Capillary trapping of gas in porous media is important for many processes such as oil recovery and gas geo-sequestration. Foam can mitigate gravity override and viscous fingering of gas by reducing its relative permeability through gas trapping. However, there are limited studies dedicated to understanding how foam assists in gas trapping, the best mode of foam injection for trapping, and its application in geo-sequestration. This paper uses an initial–residual saturation analysis to investigate foam-assisted capillary trapping during the surfactant alternating gas (SAG) injection process in saline aquifers. More specifically, we studied the effects of pore geometric properties, in situ generated foam, and surfactant concentration on gas trapping efficiency and final residual gas saturation, Sgr. First, NMR surface relaxometry measurements were carried out on the rock samples to indicate the mean pore sizes of the rocks. A series of core flooding tests, equipped with resistivity measurements, were then conducted using single-cycle gas injection followed by water injection, water alternating gas (WAG), and SAG injection methods to identify which mode of injection results in the most trapped gas. The results showed that the SAG method had a better sweep efficiency and trapped more gas than other methods. The initial–residual (IR) gas saturation relationships from SAG data measured from several rock samples were then analyzed using Land’s trapping model. Gas trapping efficiency (indicated by Land’s coefficient, C) and residual gas were also found to increase in rocks with large average pore sizes and with increasing surfactant concentration. However, increasing the surfactant concentration above a certain limit did not cause further improvement in the trapping coefficient but only increased the Sgr. The results also showed that high values of surfactant concentrations might cause a slight reduction in the foam’s apparent viscosity, which then reduces the initial gas saturation, and consequently, Sgr. Finally, a linear relationship between the Sgr and the measured log mean of surface relaxation times (T2LM) was obtained, and two correlations were proposed. Therefore, the NMR measurements can be considered a reliable prediction method for Sgr in porous media.

Relative Permeability of Hydrogen and Aqueous Brines in Sandstones and Carbonates at Reservoir Conditions

AbstractGeological hydrogen storage in depleted gas fields represents a new technology to mitigate climate change. It comes with several research gaps, around hydrogen recovery, including the flow behavior of hydrogen gas in porous media. Here, we provide the first‐published comprehensive experimental study of unsteady state drainage relative permeability curves with H2‐Brine, on two different types of sandstones and a carbonate rock. We investigate the effect of pressure, brine salinity, and rock type on hydrogen flow behavior and compare it to that of CH4 and N2 at high‐pressure and high‐temperature conditions representative of potential geological storage sites. Finally, we use a history matching method for modeling relative permeability curves using the measured data within the experiments. Our results suggest that nitrogen can be used as a proxy gas for hydrogen to carry out multiphase fluid flow experiments, to provide the fundamental constitutive relationships necessary for large‐scale simulations of geological hydrogen storage.

Sharp Transition to Strongly Anomalous Transport in Unsaturated Porous Media

AbstractThe simultaneous presence of liquid and gas in porous media increases flow heterogeneity compared to saturated flows. However, the impact of saturation on flow and transport has so far remained unclear. The presence of gas in the pore space leads to flow reorganization. We develop a theoretical framework that captures the impact of that reorganization on pore‐scale fluid velocities. Preferential flow is distributed spatially through a backbone, and flow recirculation occurs in flow dead‐ends. We observe, and predict theoretically, that this previously identified flow structure induces a marked change in the scaling of the velocity probability density function compared to the saturated configuration and a sharp transition to strongly anomalous transport. We develop a transport model using the continuous time random walk theory that predicts advective transport dynamics for all saturation degrees. Our results provide a new modeling framework linking phase heterogeneity to flow heterogeneity in unsaturated porous media.

Research method of pressure relief and permeability enhancement in low permeability coal seam: A review

Gas drainage can prevent accidents such as coal and gas outbursts and gas explosions, which is of great significance for coal mine safety production. The level of permeability directly determines the effect of gas drainage. Therefore, experts and scholars in related fields have conducted extensive research with regard to adopting different measures to increase the permeability of coal and thereby improve the efficiency of gas drainage. However, in analyzing, comparing, and summarizing the advantages, disadvantages, and adaptability of various methods, there are few review studies in the literature. First, this Review investigates the principles, processes, and effects of different methods and finds that each method has its own specific application conditions and limitations. Simultaneously, it classifies different stimulation methods according to the principle of stimulation, which are mainly divided into physical stimulation methods, chemical stimulation methods, microbial stimulation methods, and thermal stimulation methods. Then, for better field applications, this Review investigates emphatically these methods that are currently popular but still in the laboratory stage, such as acidification stimulation and freeze–thaw stimulation, and analyzes the experimental methods, principles, experimental effects, influencing factors, etc. Permeability represents the flow capacity of gas in porous media and thereby affects the efficiency of gas extraction. Therefore, this Review summarizes the influencing factor of permeability. Finally, this Review discusses the aspect that needs to be perfected and improved for different methods and points out the problems and possible development directions in the future.

Adsorption and diffusion behavior of CO2/H2 mixture in calcite slit pores: A molecular simulation study

The adsorption and diffusion of gases in porous media are fundamental phenomena that find widespread application in the energy and chemical industries. In this study, we used Grand Canonical Monte Carlo and molecular dynamics simulation methods to evaluate the adsorption and diffusion properties of CO2 and H2 in the calcite silt-like pores. We report the influence of pressure, pore size, and temperature on adsorption isotherms (i.e., total, absolute, and excess) and diffusion coefficients (i.e., self-diffusion, Fick transport diffusion, and Maxwell-Stefan diffusion). The results reveal a greater CO2 adsorption capacity compared to H2 and the easy absorption of the oxygen atoms of CO2 onto the surface of calcite. The adsorption capacities of CO2 and H2 increased together with the pressure, and the pore size had little effect on the absolute adsorption capacity and density distribution of the pure compounds. The interaction energy between calcite and CO2/H2 showed that the calcite had greater affinity for CO2 than for H2. The CO2 diffusion coefficients were smaller than those of H2. The diffusion coefficients of CO2 and the mutual diffusion coefficients of the gas mixture increased with increasing pressure before stabilizing. In contrast, the diffusion coefficients of H2 decreased with an increase in pressure.

An ICLS-based method for solving two-phase seepage free surface considering compressible gas in porous media

The current seepage free surface methods can represent the seepage free surface when the gas escapes freely, but they cannot handle this situation when involving the confined gas, because they either ignore the gas or assume that the gas is incompressible. However, the compressibility of confined gas has an important effect on the seepage free surface. To address this problem, a novel approach based on the improved conservation level set (ICLS) method is proposed to represent accurate free surface especially considering compressible gas in two-phase seepage. The water–air two phases are both governed by the seepage governing equation and the generalized Darcy's law. Considering the compressibility of gas, the air density needs to be updated as the pore gas pressure changes according to the ideal gas law. The free surface is implicitly captured by the ICLS method, which exhibits better mass conservation property and more precise surface information. The new approach can be easily generalized without limitation of discretization schemes. Regardless of whether the gas can escape freely or not, the proposed method has the ability to describe precise free surface. The accuracy and capacity of present work are validated with several numerical examples.

Effect of electro-kinetic processes on filtration of fluids and gas in porous medium

The paper reviews the fluid and gas flow in the porous medium considering electro-kinetic phenomena – electro-phoresis and electro-osmosis, as well as the charges associated with them. These phenomena are due to the double electric layer on the border of division of disperse system phases. Electro-kinetic phenomena are follows: electro-phoresis, electro-osmosis, flow potential (Quincke effect) and sedimentation potential (Dorn effect). The formulas for the motion of fluid and gas in porous medium considering the properties of porous medium and saturating them fluids, as well as the interaction between them, which is described with electro-kinematic phenomena, have been obtained. Obtained formulas have been evaluated via the results of laboratory researches.

Experimental determination of deviation factor of natural gas in natural gas reservoir with high CO2 content

The deviation factor of natural gas is a coefficient to quantitatively describe the deviation degree between real gas (natural gas) and ideal gas. Generally, the deviation factor of natural gas is measured in PVT cell without considering porous media. However, when natural gas is in underground porous media reservoir, due to the adsorption of porous media, the deviation factor of natural gas in porous media deviates from that measured in conventional PVT cell. Moreover, compared with other gases, CO2 has stronger adsorption capacity. Therefore, in porous media, the deviation factor of natural gas considering the adsorption of porous media is quite different from that measured in conventional PVT cell. In this paper, simulating the isothermal mining conditions in gas reservoir,the deviation factor of natural gas with different CO2 content considering the influence of porous media under different pressure isothermal conditions is studied by using the test of designed sand filled long slim tube in series. And under the same conditions, the deviation factor is compared with that of conventional PVT. The experimental results show that under the same conditions, due to the adsorption of porous media, the deviation factor measured in porous media is smaller than that measured by PVT cell without considering porous media.

Efficient determination of aqueous-phase gas diffusion coefficients and tortuosity in soil

Diffusion of dissolved aqueous-phase gas in porous media is increasingly relevant to existing and emerging geotechnical engineering applications. There is currently no established method to determine the effective aqueous-phase gas diffusion coefficient and associated tortuosity factor through soil. In this study, a pressure-decay method was applied to determine tortuosity factors for aqueous-phase gas diffusion in silt, sand and gravel using experimental equipment readily available in many geotechnical engineering laboratories. Inverse numerical analyses were applied to assess the effective tortuosity factor from pressure-decay data, which provided a consistent and efficient assessment of tortuosity associated with aqueous-phase gas diffusion for each soil type.

Applicable conditions of the binomial pressure method and pressure-squared method for gas well deliverability evaluation

In order to quickly and accurately evaluate gas well deliverability, it is necessary to clarify the applicable conditions of the simplified laminar-inertial-turbulent gas well deliverability evaluation method (i.e., pressure-squared method and pressure method). In this regard, this paper analyzes the PVT data, simulation wells and field case wells of typical gas reservoirs in China by reviewing the formal evolution of the flow control equation for the real gases in porous media. Then, the applicable conditions of binomial pressure-squared method and pressure method are discussed. And the following research results were obtained. First, when the pressure is lower than 14 MPa, μZ is basically a constant; and when the pressure is higher than 42 MPa,ρμZ is basically a constant. Second, the applicable range of the pressure-squared method can be increased from 14 to 20 MPa. In this case, the relative error of absolute open flow potential calculated using the pressure-squared method is less than 5% compared with the pseudo-pressure method. If the pressure is between 20 and 30 MPa, the relative error of the absolute open flow potential calculated using the pressure-squared method is less than 10%. Third, when the pressure exceeds 80 MPa, the relative error of the absolute open flow potential calculated using the pressure method is less than 10% compared with the pseudo-pressure method. If the pressure-squared method is used in the case of high pressure, the calculated absolute open flow potential is lower and the relative error is close to 25%. Fourth, in the case of low pressure, if the pressure is constant, the higher the temperature is, the smaller the relative error between the pressure-squared method and the pseudo-pressure method is. In the case of high pressure, if the pressure is constant, the higher the temperature is, the greater the relative error between the pressure method and the pseudo-pressure method. In conclusion, it is recommended to adopt the pseudo-pressure method in laminar–inertial-turbulent gas well deliverability analysis. In the case of low pressure (below 30 MPa), the pressure-squared method can be used. In the case of high pressure (above 80 MPa), the pressure method can be applied.