Permeability Evolution Research Articles

Theoretical one-dimensional porous media model for microbial growth on pore plugging and permeability evolution and its verification

ABSTRACT The growth, reproduction, and metabolic activities of microorganisms can lead to blockages within porous media, a phenomenon commonly observed in landfill engineering. Termed as microbial plugging, this phenomenon is significantly influenced by the inherent permeability characteristics of the system. In this study, we propose a simulation model based on the Monod equation to elucidate the clogging process caused by microorganisms in one-dimensional pore channels. Our primary focus is on the application of this model in landfill bioreactor systems. We demonstrate that microbial clogging in these systems is predominantly affected by factors such as the maximum environmental carrying capacity and pore size. These factors are directly influenced by the presence of solid waste within the landfill. By offering a theoretical foundation for mitigating microbial clogging in pore channels of landfill bioreactor systems, this research has the potential to contribute to the development of more efficient and effective waste management practices.

Experimental Study on the Effect of Freeze-Thaw Cycles on the Mechanical and Permeability Characteristics of Coal

The safe and efficient mining of coal seams with low porosity, low permeability, and high heterogeneity under complex geological conditions is a major challenge, with the permeability of coal seams playing a crucial role in coal mine gas extraction. The development of coal seam permeability enhancement technology can help coal mines produce safely and efficiently, while the extracted coal bed methane can be utilized as green energy. To study the effect of freezing and thawing on the evolution of the mechanical and permeability properties of coal, triaxial permeability tests were conducted on low-permeability coal under two different confining pressures. Simultaneously, dry, saturated, and freeze-thaw coal samples were set up for comparison, and the effects of water and freeze-thaw were isolated from each other. The triaxial mechanics and percolation laws of dry, saturated, and freeze-thaw coal rocks were obtained; the results show that saturated coal has the lowest initial permeability, while freeze-thawed coal has the highest initial permeability. Through analyzing the effects produced by water, freezing and thawing on coal specimens, the mechanism of the influence of freeze-thaw on the permeability evolution of coal was revealed. The research results can provide theoretical guidance for the development of gas extraction technology for low-permeability coal seams.

Influence of fracture pattern between Hot Sedimentary Aquifer (HSA) and Enhanced Geothermal Systems (EGS) on thermal production and permeability evolution

Thermal energy extraction relies on the fluid circulation and heat transfer between fluids and rock matrix. The conductive fracture channel provides effective conduits for fluid circulation, while absorbing heat energy from adjacent blocks depending on heat transfer length. The vertical depth variation not only leads to the quality of heat reservoir, but also brings substantial influence on fracture pattern due to stress state and chronological tectonic evolution. Consequently, it is vital to explore the influence of fracture pattern on the model of thermal energy production and subsequent permeability evolution. The induced thermal stress plays an important role in the stress state and fractures and therefore permeability development. It is hypothesized that the two-stage evolution of permeability and porosity: shrinkage effect from thermal cooling is strong sufficient with the highest drawdown gradient, which leads to significant minimum horizontal stress reduction and permeability enhancement. The second stage when rock temperature completely drained allows permeability and porosity reduce to the initial magnitude, with the thermal stress diminishes. The shallow geothermal extraction with less consolidation induces less thermal stress to change rock permeability and porosity. Therefore, the thermal stress needs to be taken into account in evaluating the formation properties evolution and stress state.

A preliminary study on the quality evaluation of coking coal from its structure thermal transformation: Applications of fluidity and swelling indices

Evaluating the coking coal quality from coal structure thermal transformation was crucial to control the coking process. The coal quality indices of ash composition, volatile matter, element distribution and caking indices were redefined based on the coal structural characteristics. Five structure parameters derived from volatile matter and element distribution, including carbon aromaticity (fa), average number of condensation rings (NCR), ring condensation index (2(NCR −1)/C), aliphatic hydrogen content (AlH) and number of bridge bonds (AlB), were proposed to evaluate the comprehensive structure properties of coals. The rationality of these parameters was verified through 13C NMR analysis. The superiority of fluidity and swelling indices in reflecting the structure transformation of individual and blended coals was clarified. In addition, a novel mothed for measuring swelling pressure was developed, taking into account the impact of heat and mass transfer on the coking process. The results show that the bridge bonds content (AlB) affects the coal particle softening which attributes to the thermal cleavage of Cal-Cal/O and Car-O. The high aliphatic hydrogen content (AlH) relating to the stabilization of pyrolytic fragments decreases maximum fluidity temperature. The formula of F(MD) captures the relevance among maximum dilatation, volatile matter, caking and plastic layer indices, which aids in comprehending the swelling mechanism based on the balance between gas release and permeability evolution. The fluidity and swelling indices serve as indicators of the structural transformation during individual coal coking, contributing to the quality evaluation of blended coals with similar coke performance. The self-designed device provides a more accurate prediction of pushing current based on the maximum swelling pressure, compared to the Audibert-Arnu dilatation. This work contributes to the scientific evaluation of coking coals and the precise control of the coking process.

Permeability Evolution of Anthracite Subjected to Liquid Nitrogen Treatment under Repeated Loading–Unloading Conditions

Permeability Evolution of Anthracite Subjected to Liquid Nitrogen Treatment under Repeated Loading–Unloading Conditions

Stress and permeability evolution of high-gassy coal seams for repeated mining

Coal bed methane reservoirs in China are generally characterized by high stress and low gas permeability coefficient. Protected layer mining has the effect of unloading pressure and increasing gas permeability coefficient. There are few studies in the case of repeated mining with an orthogonal arrangement of the protected layer. Based on the engineering practice of the high gas coal seams group in Xinjing coal mine, a combination of numerical simulation and field test was used. The distribution law of plastic zone, stress-strain and gas permeability coefficient of the protected layer under the two states of single mining and repeated mining were obtained. The stress and gas permeability coefficient distribution of the protected layer was divided into 5 and 6 zones in plane for single and repeated mining cases. The field test tested the distribution law of stress, gas pressure, deformation, and gas permeability coefficient, and verified the reliability of the numerical simulation results. According to the characteristics of gas permeability coefficient distribution under the condition of repeated mining, a method for accurate gas extraction is proposed. The results of the study have important implications for the design of gas extraction schemes in orthogonal repeated mining situations.

Anisotropic strain of anthracite induced by different phase CO2 injection and its effect on permeability

To study the swelling/shrinkage strain effects of different phases of CO2 when injected into anthracite and the influence that has on the dynamic evolution of coal permeability, an experimental study of coal anisotropic adsorption of CO2 was carried out by using a triaxial compression test device, and the relationship between the swelling/shrinkage strain and permeability of the coal was discussed. The results show that the adsorption strain and time of gas exposure throughout different phase states of the CO2 injected show three stages of evolutionary behavior. The adsorption swelling of the coal sample increases with rising gas pressure. The adsorption strain of coals under the action of supercritical CO2 increased by 16.28% and 17.36% against the action of subcritical CO2, respectively. The coal portrayed anisotropic characteristics during the process of adsorption-caused swelling deformation and desorption-caused contraction, and the deformation in the vertical layer direction was greater than that in the parallel layer direction, and the anisotropy gradually weakened with increasing pressure. The permeability of the coal and the temperature is a quadratic function relationship under different effective stress conditions, and there is a zone where the changes occur. The study provides a theoretical basis CO2- Enhanced coalbed methane recovery.

Scaling Mechanism and Permeability Evolution of Sandstone Reservoir

Knowledge of scaling mechanisms and the permeable behavior of rocks is highly important for geothermal energy development. In this study, the sandstone was soaked in a solution with the same chemical composition as geothermal water in Linyi City, Shandong Province. Permeability tests, scanning electron microscope tests, and nuclear magnetic resonance tests were performed on sandstone samples after different soak times (0, 30, 60, and 90 days) and temperatures (25 and 85 °C) to characterize the changes in microstructure and permeability properties. In addition, the changes in ion concentration in chemical solutions were compared. The results show that the wet mass and porosity of sandstone increase with the increase of soak time (0-70 d), and then entered the stable periods (70-90 d). As the soaking time, the medium and large pores inside the sandstone are transformed into small pores. The permeability of sandstone shows an overall decreasing trend, with the maximum decline when the soaking time is 30 d. At 25 °C, the scaling behavior is mainly involved by Ca2+, but at 85 °C Mg2+ is also involved in the scaling behavior. The scaling mechanism becomes the joint participation of Ca2+ and Mg2+. The results of the PHREEQC simulations are almost the same as the laboratory test results, indicating that sodium feldspar, potassium feldspar, and chlorite are generated slowly during the fouling process.

Experimental and numerical study of the influence of inclusion size on the drying shrinkage cracking in cementitious composites

AbstractThis study investigates the effect of inclusion size on drying shrinkage cracking in cementitious materials. A series of laboratory desiccation tests on concrete with different size of inclusions are conducted. Nondestructive X‐ray micro‐tomography images were used to reconstruct the drying‐induced shrinkage cracks of samples in desiccation tests. To better understand the mechanism of shrinkage cracking, a fully coupled hydro‐mechanical bond‐based Peridynamic model was developed that takes into account the interactions among deformation, cracking, and permeability evolution. The efficiency of the proposed model was verified through two benchmark problems. The influence of inclusion size on shrinkage cracks was numerically analyzed by reproducing experimental results and conducting a parametric study. The results indicate that, as the size of the inclusion increases, the quantity of drying induced cracks increases while the length of the cracks decreases and the average width of the cracks increases. However, the distribution of cracks appears to be unaffected by the size of the inclusion.

Experimental Study on Permeability and Deformation Characteristics of Bedding Shale under Triaxial Shear-Seepage Coupling

The bedding structure of shale is generated during the deposition and formation, which results in shales with prominent anisotropic characteristics. It depends on stability, control of oil and gas storage, and deep exploitation. In addition, the mechanical and permeability parts of bedding shale are very complex when it is under deep underground space with coupled high stress and high seepage. In this study, the black bedding shale was used as the research object, and a series of triaxial shear-seepage coupling tests were carried out. Firstly, the triaxial shear stress-shear strain curves and permeability-shear stress curves of different bedding shales under other triaxial shear-seepage coupling conditions were obtained. Secondly, the failure characteristics and shear deformation characteristics of shale under the shear-seepage coupling effect were explored. The shear stress threshold and permeability evolution law at each stage of shear failure were discussed. Thirdly, the shear strength, failure mode, and mechanism parameters of the black bedding shale under different normal stress and seepage pressure were studied. Fourthly, the linear M-C criterion, Ramamurthy criterion, and Hoek-Brown criterion characterize the variation of damage strength of shale with bedding orientation under triaxial shear-seepage coupling. Those results provide an experimental basis for exploring the anisotropic mechanical characteristics and failure mechanism of bedding shale under shear-seepage coupling.

Dynamic evaluation of microscopic damage and fluid flow behavior in reservoir shale under deviatoric stress

This study presented a three-dimensional reconstruction method for digital shale cores in detail and examined the impact of deviatoric stress on the microscopic damage and fluid flow behavior in reservoir shale under deviatoric stress. In particular, this paper investigated the distribution of damage, deformation, and stress in shale under different deviatoric stresses. In addition, the characteristics of fluid velocity and pressure distribution under deviatoric stress and permeability evolution were discussed. The results showed that: (1) The deformation and damage in digital cores increased with the deviatoric stress, and the pore area will be more affected by deviatoric stress than the matrix area. (2) The fluid velocity distribution varies significantly between the matrix and the pore area, and the flaky connected fracture will aggravate this difference. (3) The fluid velocities of digital cores D1 and D2 decreased first and then increased with the increase of the deviatoric stress. (4) The permeability of digital cores D1 and D2, as the deviatoric stress increased, initially decreased due to rock deformation but subsequently increased due to the increasing damage.

Optimization of Roadside Unit Deployment on Highways under the Evolution of Intelligent Connected-Vehicle Permeability

With the increasing number of Connected and Autonomous Vehicles (CAVs), the heterogeneous traffic flow on highways now consists of a mix of CAVs and Non-networked Autonomous Vehicles (NAVs). The current deployment of Roadside Units (RSUs) on highways is mostly based on uniform or hotspot locations. However, when the permeability of CAVs on the road varies, the communication network may face challenges such as excessive energy consumption due to closely spaced RSU deployments at high CAV permeability or communication interruptions due to widely spaced RSU deployments at low CAV permeability. To address this issue, this paper proposes an improved D-LEACH clustering algorithm based on vehicle clustering; analyzes the impact of RSU and vehicle communication radius, mixed traffic density, and different CAV permeabilities in the heterogeneous traffic flow on the RSU deployment interval; and calculates the rational and effective RSU deployment interval schemes under different CAV permeabilities on highways in the heterogeneous traffic flow. When the heterogeneous traffic flow density is stable and CAV continues to penetrate, the RSU communication radius and deployment interval can be adjusted to ensure that the network connectivity is maintained at a high level. When the RSU and vehicle communication radius are stable, the mixed traffic density is 0.05, and the CAV permeability is 0.2, the RSU deployment interval can be set to 1235 m; when the mixed traffic density is 0.08 and the CAV penetration rate is 0.7, the RSU deployment interval can be set to 1669 m to ensure that the network connectivity is maintained at a high level.

Unloading-induced permeability recovery in rock fractures

Underground space creation and energy extraction, which induce unloading on rock fractures, commonly occur in various rock engineering projects, and rock engineering projects are subjected to high temperatures with increasing depth. Fluid flow behavior of rock fractures is a critical issue in many subsurface rock engineering projects. Previous studies have extensively considered permeability evolution in rock fractures under loading phase, whereas changes in fracture permeability under unloading phase have not been fully understood. To examine the unloading-induced changes in fracture permeability under different temperatures, we performed water flow-through tests on fractured rock samples subjected to decreasing confining pressures and different temperatures. The experimental results show that the permeability of fracture increases with unloading of confining pressure but decreases with loading-unloading cycles. Temperature may affect fracture permeability when it is higher than a certain threshold. An empirical model of fracture hydraulic aperture including two material parameters of initial normal stiffness and maximum normal closure can well describe the permeability changes in rough rock fracture subjected to loading-unloading cycles and heating. A coupled thermo-mechanical model considering asperity damage is finally used to understand the influences of stress paths and temperatures on fracture permeability.

Effects of thermal damage on natural gas transport capacity of tight sandstone after electrical heating

As an environment-friendly method, downhole electric heating can cause thermal damage to the rock around the well, so as to improve the gas transport capacity of tight sandstone gas reservoir (TGR), but its mechanisms are not well established. In the present study, a comprehensive analysis of the thermal damage characteristics of tight sandstones has been conducted, employing a suite of microscopic investigative techniques such as differential thermal gravimetry, X-ray diffraction, and scanning electron microscopy. The experimental results were related to permeability test results and then combined with constant-pressure heating acoustic rock tests. Subsequently, the heating and cooling processes along with the effects of confining pressure on the damage evolution and gas transport capacity were analysed. According to the difference in thermal damage mechanism, three temperature ranges were identified: 100–300 °C, 300–1000 °C, and 1000–1200 °C. In the first stage, free water escaped, clay minerals expanded, and a small number of weak cementation cracked, resulting in a 26.18% decrease (200 °C) and a 56.95% increase (300 °C) in permeability. In the second stage, the clay minerals were stripped of their bound water; with an increase in temperature, heat-induced cracks were initiated, propagated, and aggregated to form a network. The permeability increased exponentially by 938-fold. Finally, in the third stage, with the initiation of feldspar melting, the mineral surface was smooth; furthermore, permeability increased rapidly by 164.08%, after which the pores were blocked rapidly. Acoustic tests under constant-pressure heating conditions showed that thermal damage continued to evolve during the cooling phase because of the temperature variable stress. External pressures could only partially limit the evolution of thermal damage. The findings of this study illustrate that downhole electric heating (300–1000 °C) can improve natural gas transport capacity by eliminating water phase trap damage and creating a multi-scale crack network in a near-wellbore area. In addition, the nonlinear evolution of permeability in tight sandstones is different from that in other rocks, and the S-wave attenuation coefficient can well characterise this phenomenon. Thus, a mathematical model of nonlinear permeability evolution based on the principle of dual percolation is derived. Therefore, the results of this research provide a reference for the temperature selection and acoustic monitoring of the TGR downhole heating process.

Diagenesis and petrophysics of Miocene sandstones within southern Apennines foreland, Italy

Deep-marine clastic turbidite beds commonly occur in the Southern Apennines and record the main tectonic phases associated with the structural evolution of the area. Based on variations of detrital compositions through time, the sandstone suites are traditionally subdivided into four petrofacies: (I) quartzolithic (Burdigalian-Langhian), (II) quartzofeldspatholithic (Langhian-Tortonian), (III) quartzofeldspathic (Serravallian-Tortonian), and (IV) arkose (Tortonian-Messinian) sandstones. Since the complexity and diversity of these sandstone petrofacies, we aim to investigate their major diagenetic events and relate them with their detrital modes and physical properties in order to obtain key basic information at a regional scale, to better understand the main controls on petrophysical properties in this and in similar contexts. The petrophysical analysis reveals that the quartzolithic sandstones have the lowest porosity values, with a median of 4.56%. In contrast, porosity increases to median values of 16.75% in the quartzofeldspathic and arkosic petrofacies. The median permeability values range between 4.85 and 236.38 mD, and its distribution is generally poorly correlated with any other petrophysical parameter. The most widespread diagenetic minerals observed are carbonates, clay minerals, Fe-oxides and hydroxides, and less quartz. These sandstones are characterized by high compaction, which is the primary factor controlling porosity loss since the early diagenetic phases. In contrast, the early precipitation of pore-filling carbonate cement is assumed to have partly reduced the effect of compaction in quartzolithic and arkosic sandstones. Nonetheless, variations in petrophysical features among petrofacies can be traced back to the detrital composition, with the highest but less effective porosity associated with the presence of ductile grains, siliciclastic matrix and feldspars. Accordingly, this study reveals how linking detrital modes to the key petrophysical parameters may help obtain significant information about the regional control on the evolution of porosity and permeability in clastic turbiditic wedges of foreland domain settings as a baseline useful to further local and detailed studies.

Pressure-driven processes explain the decreasing magnetization of the subducting oceanic crust in the Japan Trench

Despite the decreases in temperature and permeability of oceanic plates with increasing age, hydrothermal circulation (HC) can be rejuvenated in the 130-Ma old Pacific plate in the vicinity of the Japan Trench, substantially affecting the thermal structure and remaining amount of magnetization (RAM). To decipher the roles of HC in the thermal structure and the RAM, the vigor and extent of HC in the vicinity of the Japan Trench should be quantitatively evaluated. Here we numerically show that HC is rejuvenated in the outer-rise zone but ceases after subduction owing to permeability evolution. The calculated thermal structure explains the measured heat flow evolution but negates the HC-driven thermal demagnetization, which was thought to decrease the RAM after subduction. Instead, we propose that the pressure-driven processes decrease the RAM after subduction through the demagnetizations of titanomaghemite and magnetite and the mineral phase transitions from maghemite to hematite.

Application of Image Processing in Evaluation of Hydraulic Fracturing with Liquid Nitrogen: A Case Study of Coal Samples from Karaganda Basin

Research of microstructure and permeability evolution of coal following LN2 treatment elucidate the process of cryogenic fracturing due to environmentally friendly behavior in comparison with conventional hydraulic fracturing. The evolution of the 2D microstructure of bituminous coal before and after LN2 treatment was examined using a high-resolution camera. The image processing was implemented using functions from the OpenCV Python library that are sequentially applied to digital images of original coal samples. The images were converted into binary pixel matrices to identify cracks and to evaluate the number of cracks, crack density, total crack area, and average crack length. Results were visualized using Seaborn and Matplotlib Python libraries. There were calculations of total crack area (TCA), total number of cracks (TNC), crack density (CD), the average length of cracks (Q2), first (Q1) and third (Q3) quartiles in fracture length statistics. Our findings demonstrate a progressive increase in the Total Crack Area (δTCA) with longer freezing times and an increased number of freezing–thawing cycles. In contrast, the change in crack density (δCD) was generally unaffected by freezing time alone but exhibited a significant increase after several freezing–thawing cycles. Among the freezing times investigated, the highest crack density (CD) value of 300 m−1 was achieved in FT60, while the lowest CD value of 31.25 m−1 was observed in FT90 after liquid nitrogen (LN2) treatment. Additionally, the FTC4 process resulted in a 50% augmentation in the number of cracks, whereas the FTC5 process tripled the number of small cracks.

Impact of permeability evolution in igneous sills on hydrothermal flow and hydrocarbon transport in volcanic sedimentary basins

Abstract. Sills emplaced in organic-rich sedimentary rocks trigger the generation and migration of hydrocarbons in volcanic sedimentary basins. Based on seismic and geological observations, numerical modeling studies of hydrothermal flow around sills show that thermogenic methane is channeled below the intrusion towards its tip, where hydrothermal vents nucleate and transport methane to the surface. However, these models typically assume impermeable sills and ignore potential effects of permeability evolution in cooling sills, e.g., due to fracturing. Here, we combine a geological field study of a volcanic basin (Neuquén Basin, Argentina) with a hybrid finite-element–finite-volume method (FEM–FVM) of numerical modeling of hydrothermal flow around a sill, including hydrocarbon generation and transport. Our field observations show widespread veins within sills composed of graphitized bitumen and cooling joints filled with solid bitumen or fluidized shale. Raman spectroscopy indicates graphitization at temperatures between 350 and 500 ∘C, suggesting fluid flow within the intrusions during cooling. This finding motivates our modeling setup, which investigates flow patterns around and through intrusions that become porous and permeable upon solidification. The results show three flow phases affecting the transport of hydrocarbons generated in the contact aureole: (1) contact-parallel flow toward the sill tip prior to solidification, (2) upon complete solidification, sudden vertical “flushing” of overpressured hydrocarbon-rich fluids from the lower contact aureole towards and into the hot sill along its entire length, and (3) stabilization of hydrocarbon distribution and fading hydrothermal flow. In low-permeability host rocks, hydraulic fracturing facilitates flow and hydrocarbon migration toward the sill by temporarily elevating porosity and permeability. Up to 7.5 % of the generated methane is exposed to temperatures >400 ∘C in the simulations and may thus be permanently stored as graphite in or near the sill. Porosity and permeability creation within cooling sills may impact hydrothermal flow, hydrocarbon transport, and venting in volcanic basins, as it considerably alters the fluid pressure configuration, provides vertical flow paths, and helps to dissipate overpressure below the sills.

Apparent Permeability Evolution Due to Colloid Migration Under Cyclic Confining Pressure: On the Example of Porous Limestone

Apparent Permeability Evolution Due to Colloid Migration Under Cyclic Confining Pressure: On the Example of Porous Limestone

Experimental investigation on mechanical behavior, energy evolution and gas permeability of anisotropic phyllite subjected to triaxial compression and cyclic loading

The bedding plane direction significantly affects the mechanical properties, deformation and gas permeability evolution of rock mass in gas storage engineering. In this paper, for phyllite, a series of triaxial compression with cyclic loading and gas permeability apparatus are conducted to investigate such directional effect. The peak stress, Young’s modulus, energy evolution, failure mode and gas permeability coefficient are analyzed. For triaxial compression test, with increasing inclination angles, the deformation parameters (E, E50, μ) and characteristic stress parameters (σcc, σci, σcd) both show a U-shape pattern. For triaxial cyclic loading test, the peak stress of specimen first decreases and then increases, i.e., the peak stresses at the inclination angles of 0°, 30°, 45°, 60° and 90° are 118.18, 84.35, 64.18, 42.54 and 84.57 MPa, respectively. The energy evolutions of specimens at different inclination angles are similar, but increase with increasing cyclic number. i.e., when β=60°, with the cycle number increasing from 1 to 3, the elastic strain energy, the dissipated strain energy and the total strain energy increase by 343.55%, 175.08%, and 259.87%, respectively. In addition, the failure mode of phyllite specimens is analyzed and summarized as three distinct types, i.e., tensile-shear failure, shear-sliding failure and split-shear failure. The relationships between the initial gas permeability and confining pressure, deviatoric stress show positive correlations. The failure of layered phyllite is most likely to occur at a bedding plane inclination angle of 45° to 60°.