Mechanism Of Permeability Evolution Research Articles

The permeability evolution mechanism of ore-bearing strata during acid in-situ leaching of uranium: A case study of Bayanwula uranium mine in Inner Mongolia of China

Uranium mainly comes from ISL of sandstone-type uranium deposits in China. The change of porosity and permeability caused by blockage of ore-bearing strata is one of the most serious problems in acid ISL of uranium. In this paper, the groundwater tracer test was carried out before and 1 year after ISL to explore the pore and permeability evolution characteristics of the ore-bearing layer during ISL. The test results showed that the leaching solution migrated along two seepage channels and the water-bearing medium was isotropic. After 1 year of ISL, the flow rate of the leaching solution decreased obviously. However, the flow rate of the leaching solution in slower channel decreased more than that in the faster channel in all directions, which was caused by the more adequate chemical reactions between the leaching solution and the minerals of the ore-bearing layer and the more corresponding precipitation in the slower channel. In addition, the flow rate along the direction of groundwater flow decreased less than that in the direction of vertical groundwater flow. This was closely related to the transformation of aquifer medium by hydrodynamic field. Initial stage of ISL, the occurrence of plugging is closely related to the precipitation-dissolution process of iron and aluminum minerals under the change of pH, which is accompanied by the continuous precipitation of gypsum.

Investigating the Creep Damage and Permeability Evolution Mechanism of Phyllite Considering Non-Darcy’s Flow

This study investigates the intricate interplay of hydraulic coupling, creep damage, and permeability evolution mechanisms in phyllite, focusing on their relevance to tunnel engineering design and long-term stability in soft rock formations. To achieve this, conventional triaxial tests were conducted on saturated phyllite specimens under creep-seepage acoustic emission conditions. The results were systematically analyzed to unveil the inherent characteristics of creep deformation, seepage rate evolution, and damage progression in phyllite when subjected to stress–seepage coupling. Furthermore, a permeability model for representative volume element (RVE) was developed based on meso-mechanics principles, considering the distinctive attributes of low-permeability non-Darcy’s flow in rock. Consequently, a novel relationship between effective damage and permeability was established. We determined that seepage pressure induces three key effects on the creep damage mechanism of phyllite samples: (1) It adds to the existing stress through the superposition of osmotic pressure and axial load, (2) it induces tensile expansion stress because of pore water pressure, and (3) it softens the fracture surfaces to some extent. More importantly, this study validates the relationship between effective damage and permeability through the fitting of creep and damage parameters, which were obtained from the test results, and it reveals a square relationship between subsequent damage and permeability under stress conditions. The findings of this study provide a robust theoretical foundation for comprehending the evolution of damage and permeability characteristics during the creep process of rock under seepage conditions. We obtained essential insights and quantitative analyses for comprehending the damage mechanisms in rock creep under hydraulic coupling, which has significant implications for tunnel engineering and long-term rock stability assessments in soft rock environments.

Permeability evolution mechanism and the optimum permeability determination of uranium leaching from low-permeability sandstone treated with low-frequency vibration

Permeability evolution mechanism and the optimum permeability determination of uranium leaching from low-permeability sandstone treated with low-frequency vibration

Fracture propagation and permeability evolution mechanism of jointed rock mass in coastal mines

Fracture propagation and permeability evolution mechanism of jointed rock mass in coastal mines

Combined Effects of CO2 Adsorption-Induced Swelling and Dehydration-Induced Shrinkage on Caprock Sealing Efficiency.

Carbon dioxide (CO2) may infiltrate into the caprock and displace brine water in the caprock layer. This causes two effects: one is the caprock swelling induced by the CO2 adsorption and the other is the caprock dehydration and shrinkage due to CO2-brine water two-phase flow. The competition of these two effects challenges the caprock sealing efficiency. To study the evolution mechanism of the caprock properties, a numerical model is first proposed to investigate the combined effects of CO2 adsorption-induced expansion and dehydration-induced shrinkage on the caprock sealing efficiency. In this model, the caprock matrix is fully saturated by brine water in its initial state and the fracture network has only a brine water-CO2 two-phase flow. With the diffusion of CO2 from the fractures into the caprock matrix, the CO2 sorption and matrix dehydration can alter the permeability of the caprock and affect the entry capillary pressure. Second, this numerical model is validated with a breakthrough test. The effects of the two-phase flow on the water saturation, CO2 adsorption on the swelling strain, and dehydration on the shrinkage strain are studied, respectively. Third, the permeability evolution mechanism in the CO2-brine water mixed zone is investigated. The effect of dehydration on the penetration depth is also analyzed. It is found that both the shale matrix dehydration and CO2 sorption-induced swelling can significantly alter the sealing efficiency of the fractured caprock.

Characteristics of Elastoplastic Consolidation by Compaction and Its Effects on Coal Permeability

This paper presents a combined experimental–analytical investigation of coal strain development under fluctuating applied hydrostatic stress. The laboratory setup mimics the isotropic volumetric compaction of coal under burial–uplift cycles in the absence of tectonic stress. Special emphasis is placed on the corresponding permeability evolution of the coal strata. Our results show that the stress–strain path is exponential, approaching a linear relation in the logarithmic stress–strain space with the monotonic increase in stress. A similar behavior is found for the strain–permeability path in the logarithmic strain–permeability space. The permeability recovery undergoes hysteresis with respect to the stress in a stress loading–unloading cycle, but the hysteresis is not manifest with respect to the strain. A theoretical geomechanical consolidation analysis was performed using an elastoplastic modelling framework. The analysis suggests that plastic strain is the cause of the hysteresis of the strain recovery in a stress loading–unloading cycle. The closed hysteresis loops manifested in stress loading–unloading–reloading cycles are promoted by the plastic strain during stress unloading and the difference in evolution rates of the elastic core between loading and unloading. The results of this study are helpful for understanding the mechanism of permeability evolution and optimizing water and coal seam gas production.

Similar simulation test study on permeability evolution mechanism of fault sliding fracture zone

Similar simulation test study on permeability evolution mechanism of fault sliding fracture zone

Study on permeability evolution mechanism of aquifer coal seam roof sandstone under plastic flow

Study on permeability evolution mechanism of aquifer coal seam roof sandstone under plastic flow

Analysis of permeability evolution mechanism during CO2 enhanced coalbed methane recovery based on impact factor method

To studying the influence of CO2 injection on CBM recovery and reservoir permeability, a hydraulic-mechanical-thermal coupling numerical model considering gas flow, competitive adsorption, temperature, and coal deformation was established. The model validation was carried out first, then the CO2 enhanced CBM recovery (CO2-ECBM) processes under different injection pressure and temperature were simulated, and the characteristics of CH4 output and reservoir permeability evolution were analyzed. Finally, the impact factor method for quantitative evaluating the contribution of critical parameters was proposed based on the porosity model. The results show that the production increases with the increase of injection pressure. When the injection pressure is 4 MPa, the production increases by 27,860 m3. When the injection pressure was not higher than the initial reservoir pressure, the coal matrix's deformation was dominated by CH4 desorption. When the injection pressure was higher than the initial reservoir pressure, the deformation was dominated by CH4 desorption, and the permeability increased at the preliminary stage. As time increased, the relative impact factor of CH4 desorption (RIFD) decreased, and the relative impact factor of CO2 adsorption (RIFA) increased; the deformation was dominated by CO2 adsorption, so the permeability decreased. The relative impact factor of pore pressure (RIFP) decreases with the increase of injection pressure, and its maximum value is only 0.014. The microscopic mechanism of permeability evolution was analyzed in this paper from the perspective of coal matrix deformation. The results can provide a theoretical reference for the parameter optimization of CO2-ECBM engineering applications.

In-situ X-ray tomography on permeability evolution of C/SiC porous ceramic for hypersonic vehicles

Transpiration cooling system in hypersonic vehicles still remains a challenge due to the limitations of observing permeability and microstructure evolution of porous medium filled with coolant. To tackle this problem, a novel compression-permeation device is designed with high-resolution X-ray tomography system, and then an investigation on permeability evolution mechanism of a C/SiC porous ceramic under pressure is performed using in-situ X-ray imaging and the compression-permeation device. The experimental results indicate that the pore-space fluid flow is displayed in terms of three-dimensional streamlines, making the permeability mechanism clear. Meanwhile the porosity along the thickness of ceramic under pressure has been obtained by synchrotron tomography testing, and it is also verified that the porosity of C/SiC ceramic fabricated in our research group is basically uniform (>95.4%) along the thickness. Furthermore, we have found the evolution rule for permeability of porous ceramic with water, which depends on the variation of its microstructure under different loads.

Experimental Study on Seepage Characteristics of Jurassic Weakly Cemented Sandstone under Water-Rock Interaction

As unconventional water-bearing rocks, the hydraulic conductivity of weakly cemented sandstones can increase by several orders of magnitude during drainages or pumping tests, posing great challenges to water prevention and control of coal mines in northwestern China. In this study, seepage experiments on Jurassic weakly cemented sandstones were performed and the hydraulic conductivity during the seepage process was analyzed. Combined with laboratory test and theoretical analysis methods, the relation between the permeability and micropore structures was studied, and the permeability evolution mechanism of the weakly cemented sandstones was eventually clarified. According to the experimental results, the seepage process can be divided into the saturated seepage stage, the stable seepage stage, and the seepage mutation stage. The hydraulic conductivity increases as the porosity and the mercury extrusion rate increase, but there is no obvious correlation between them that can be identified. In contrast, there is a linear positive correlation between the hydraulic conductivity and the average pore-throat radius. The variation trend of the pore-throat ratio can be used as the main reference indicator for judging whether the seepage mutation occurs in weakly cemented sandstone. Based on the correlation analysis of micropore structures and the hydraulic conductivity, a seepage model of straight capillary was constructed and the theoretical permeability equations of stable seepage stage and seepage mutation stage were proposed. It is concluded that the specific permeability of weakly cemented sandstones is directly proportional to porosity and the square of the average pore-throat radius. A theoretical equation to calculate the specific permeability during the latter two stages was also presented in this paper. Theoretical calculation results are roughly consistent with actual values obtained in the experiments.

Permeability evolution and mechanism of thermally damaged basalt fiber-reinforced concrete under effective stress

This paper presents an experimental study of the permeability evolution of thermally damaged basalt fiber-reinforced concrete (BFRC) under effective stress. Initial permeability, temperature damage coefficient, stress sensitivity, and maximum permeability damage rate of BFRC increased gradually with temperature, while they decreased with the increased cycles of effective stress loading and unloading. The permeability of BFRC shows nonlinear attenuation in the effective stress loading stage, and the permeability recovery degree of BFRC decreases with the decrease of effective stress in the unloading stage. The mechanism of permeability evolution is revealed based on the changes in pore characteristics.

Numerical simulation of damage and permeability evolution mechanism of coal seam under microwave radiation

Microwave heating is an effective method to improve the recovery rate of coalbed CH4. In this study, a fully coupled electromagnetic thermodynamic model was developed to study the effects of coal compaction, thermal expansion and thermal gas desorption on coal deformation. The simulation results show that although in the initial stage, the decrease of gas pressure by microwave is not obvious, the distribution of gas pressure in coal seam is obviously affected by microwave after a period of time. The microwave can also affect the mineral composition of rocks, cause rock damage, promote the development of cracks, and promote the increase of permeability

Analysis of seepage evolution law of rock mass based on the numerical algorithm considering strength weakening water absorption

Conventional numerical methods for modeling water seepage hardly provide a realistic description for the associated degradation of rock material and the permeability evolution mechanism. A numerical algorithm was utilized to investigate the rock seepage evolution process and the course of deformation failure. A theoretical model for depicting the weakening of rocks modulus and strength caused by water absorption in rock substrate was developed, and the mathematical relationships are presented in this paper. The softening process of a siltstone specimen due to water absorption was simulated under low- and high-fluid pressures as the boundary condition based on the theoretical model. Moreover, uniaxial compression test was performed for the specimen under different time of water absorption. The results indicated that the higher the fluid pressure, the quicker that the rock specimen reached saturation. It was observed that at the beginning of a seepage process, the openings are mainly filled by free water, but as time proceeds, there is a transition from absorption of free water in openings to water absorption by rock substrate. Fluid pressure, as the boundary condition, has a controlling effect on seepage rate but barely has any effect on the rate of water absorption in rock substrate. As the time of water absorption increases, rock strength (cohesion and angle of internal friction) decreases gradually until reaching the residual value. The numerical estimation of the changes in water content of rock substrate over time agrees with the theoretical explanations, which indicates high precision of the developed numerical method.

Mechanism of Permeability Evolution for Reservoir Sandstone with Different Physical Properties

Permeability of sandstones with different properties taken from Chongqing reservoirs has been measured and deeply discussed under increasing deviatoric stress. Corresponding to the distinct features in the stress-strain behaviors, the permeability of sandstones is found to evolve with a clear permeability decrease in the initial closure region, a constant permeability value in the elastic region, a permeability increase in the crack initiation and propagation region, a sharp permeability increase in the crack growth region, and a decrease permeability in the residual stage. The results also show that the variation patterns of permeability are similar for two reservoir sandstones under combination of confining pressure and water pressure; however, the strength and permeability are smaller for the sandstone with mud than that without mud, deeply indicating that mud-like materials have a relatively great impact on the mechanical properties and permeability, so mud components cannot be ignored for prediction of reservoir permeability. Furthermore, a statistical damage constitutive model considering hydraulic-mechanical coupling process is presented to calculate the damage variable D, illustrating that larger water pressure will result in a relatively smaller damage variables D and corresponding maximum, which explains that the permeability increases more rapidly and is larger for the sandstone without mud than that with mud, and sandstone damage related to corresponding circumferential crack strain and permeability has been investigated, also implying the evolution mechanism of permeability for two sandstones with different physical properties. Therefore, it is worth pointing out that rock physical properties have a great influence on the reservoir permeability under complex extraction conditions and cannot be ignored, which is necessary to improve the recovery ratio and productivity.

Gas Permeability Evolution Mechanism and Comprehensive Gas Drainage Technology for Thin Coal Seam Mining

A thin coal seam mined as a protective coal seam above a gas outburst coal seam plays a central role in decreasing the degree of stress placed on a protected seam, thus increasing gas permeability levels and desorption capacities to dramatically eliminate gas outburst risk for the protected seam. However, when multiple layers of coal seams are present, stress-relieved gas from adjacent coal seams can cause a gas explosion. Thus, the post-drainage of gas from fractured and de-stressed strata should be applied. Comprehensive studies of gas permeability evolution mechanisms and gas seepage rules of protected seams close to protective seams that occur during protective seam mining must be carried out. Based on the case of the LongWall (LW) 23209 working face in the Hancheng coal mine, Shaanxi Province, this paper presents a seepage model developed through the FLAC3D software program (version 5.0, Itasca Consulting Group, Inc., Minneapolis, MI, USA) from which gas flow characteristics can be reflected by changes in rock mass permeability. A method involving theoretical analysis and numerical simulation was used to analyze stress relief and gas permeability evolution mechanisms present during broken rock mass compaction in a goaf. This process occurs over a reasonable amount of extraction time and in appropriate locations for comprehensive gas extraction technologies. In using this comprehensive gas drainage technological tool, the safe and efficient co-extraction of thin coal seams and gas resources can be realized, thus creating a favorable environment for the safe mining of coal and gas outburst seams.

Gas permeability evolution mechanism during creep of a low permeable claystone

Clayey rocks, due to its low permeability and self-sealing ability, have been selected as a privilege candidate host rock for underground radioactive waste repository in many countries. The gas permeability evolution is very sensitive to the deformation process in such rocks and can be used as a good indicator of microstructure changes such as the growth of micro-cracks. In this work, the mechanism of gas permeability evolution in the Callovo-Oxfordian (Cox) claystone during a creep deformation is investigated. Firstly, multi-step creep tests with different confining pressures are carried out to characterize gas permeability evolutions under different levels of the deviatoric stress. Secondly, in order to minimize effects of multiple deviatoric loading steps, one-step creep tests are also realized. Throughout all creep tests, the gas permeability is measured by a transient pulse decay method in together with the axial and radial strains. It is first found that the gas permeability of the claystone significantly decreases with the confining pressure or hydrostatic stress. The gas permeability in multi-step creep tests can exhibit a four-stage evolution with the progressive increase of deviatoric stress level, composed of a rapid decrease, a gentle decrease, a gentle increase and a rapid increase. However, the gas permeability is continuously decreasing during one-step creep tests. The permeability change in a one-step creep test can be well correlated with the volumetric strain variation by a logarithmic function. Effects of loading orientation with respect to claystone bedding planes are also investigated.

Irregular isograds, reaction instabilities, and the evolution of permeability during metamorphism

Numerical models of two-dimensional heterogeneous reactive transport of H 2 O-CO 2 fluid and oxygen isotopes were developed to investigate the heterogeneity of fluid flow and permeability attending contact metamorphism of siliceous dolomites. Comparison of results with observations from the Alta (Utah) contact aureole indicates that both mineral reactions and isotopic alteration record fluid flow through highly heterogeneous permeability. We interpret this extreme heterogeneity to be the result of positive feedback between reaction enhancement of permeability and flow-focusing. Similar distributions of mineral assemblages and stable isotopic alteration in other aureoles suggest that this is a common mechanism of permeability evolution during contact metamorphism of carbonate rocks. Flow-focusing requires fast reaction rates and slow compaction relative to fluid flow. More homogeneous permeability recorded in regional metamorphic rocks may reflect fundamental differences in the relative rates of fluid flow and compaction in regional and contact metamorphic environments.