Investigation on effective stress coefficients and stress sensitivity of different water-saturated coals using the response surface method

Han, Jun; Wu, Caifang; Jiang, Xiuming; Fang, Xiaojie; Zhang, Shasha

doi:10.1016/j.fuel.2022.123238

Cited by 15 publications

(20 citation statements)

References 67 publications

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“…Finally, a fractal apparent permeability model for coal was established by using the simple Klinkenberg equation. Subsequently, the newly developed model was verified by the experimental data provided by Han et al Further, the linkage between the coupling mechanisms of stress and water, the slippage effect, and coal permeability was analyzed, which was verified by pore radius and dynamic fractal dimensions as the connecting link between the preceding and the following. The purpose of this paper was to establish the chain reactions among various parameters to gain an in-depth understanding of the evolution mechanisms relating to coal permeability so as to provide theoretical support for deep CBM exploitation.…”

Section: Introductionmentioning

confidence: 90%

“…After ensuring the reliability of the critical capillary radius, the experimental data provided by Han et al 45 were selected to verify the fractal apparent permeability model. The coal samples were taken from the Sihe coalfield located in the south of the Qinshui Basin, where the main gas producers for the CBM wells were located.…”

Section: Verification Of the Apparent Permeability Modelmentioning

confidence: 99%

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Fractal Apparent Permeability Model for Coal under the Coupling Actions of Stress and Water

Duan

Gao

et al. 2023

Energy Fuels

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The environment of coal reservoirs is complex and variable, with various factors, not independent, but interlocking and coupled. However, their coupling effects have rarely been considered in previous theoretical studies. In addition, when a fractal theory was applied to analyze the permeability of coal, the linkage between fractal dimensions and the pore radius under external factors has usually been ignored. In this study, two parameters, pore compressibility and dynamic water saturation, were introduced to quantitatively represent the internal interactions between stress and water. Based on the results, dynamic fractal dimensions under the coupling actions of stress and water were obtained by considering variation in the pore radius and the assignment status of gas and water, following which an apparent permeability model of coal, with dynamic fractal dimensions, was established. The newly developed model was verified by reference to published experimental data. The results showed that stress dominated changes in the fractal dimension for pore-size distribution under the coupling actions of stress and water; however, changes in the fractal dimension for tortuosity was dominated, in turn, by stress and water. Subsequently, it was found that the fractal apparent permeability model could match the experimental data well. It revealed that the newly developed model could predict the evolution of coal permeability under dynamic changes in stress and water. Further, under the coupling actions of stress and water, the apparent permeability of coal possessed a positive correlation with the fractal dimension for pore-size distribution or water-dominated fractal dimension for tortuosity, while it was negatively correlated with the critical capillary radius or stress-dominated fractal dimension for tortuosity. In addition, the evolution of the apparent permeability was consistent with specific fractal dimensions and dynamic fractal dimensions, but the evolution of the slippage factor revealed an opposite result. Consequently, this initiates a new analytical perspective into investigating change mechanisms relating to coal permeability.

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Section: Introductionmentioning

confidence: 90%

Section: Verification Of the Apparent Permeability Modelmentioning

confidence: 99%

Fractal Apparent Permeability Model for Coal under the Coupling Actions of Stress and Water

Duan

Gao

et al. 2023

Energy Fuels

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“…Nowadays, the experiments on the seepage characteristics of coal are mainly carried out from different stress loading conditions, different types of coals, different seepage media, etc. − Among them, most of the experiments that study the relationship between coal permeability and stress. − Such as triaxial seepage tests can be carried out to reveal the seepage characteristics of coal under triaxial stress; − It can also study the evolution mechanism of coal permeability by controlling the cyclic load; − different loading conditions can also be designed to study the seepage characteristics of coal under different stress environments. , In addition to the stress experimental study, there are experimental studies that analyze the relationship between the water saturation of coal and the effective stress coefficient and stress sensitivity by controlling the different water saturation of coal and comparative seepage experimental studies that control different seepage media. , These experimental studies can reveal the seepage characteristics of coal. However, it can be seen that these experiments are all based on the external environment of coal.…”

Section: Introductionmentioning

confidence: 99%

“…19 , 20 In addition to the stress experimental study, there are experimental studies that analyze the relationship between the water saturation of coal and the effective stress coefficient and stress sensitivity by controlling the different water saturation of coal and comparative seepage experimental studies that control different seepage media. 21 , 22 These experimental studies can reveal the seepage characteristics of coal. However, it can be seen that these experiments are all based on the external environment of coal.…”

Section: Introductionmentioning

confidence: 99%

Experimental Study on the Variation Mechanism of Permeability and Seepage Characteristics of High-Rank Coal with Different Bedding

Liu

Nie

et al. 2022

ACS Omega

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In order to understand the variation mechanism of permeability and seepage characteristics of high-rank coal with different bedding, we prepared cylindrical raw coal samples according to the bedding angles of 0, 30, 45, 60, and 90° and conducted permeability tests under two stress paths (stress path 1, unloading confining pressure under constant axial pressure; stress path 2, simultaneous loading axial pressure and unloading confining pressure). The results show that the relationship between the permeability and effective stress of high-rank coal with different bedding in the two stress paths conforms to an exponential function, and the permeability increases gradually with an increase in differential stress. Under the two stress paths, the initial permeability of different bedding under the loading axial pressure and confining pressure shows a pattern of a maximum for parallel bedding coal samples, followed by oblique bedding coal samples, and a minimum for vertical bedding coal samples. Under path 1, the increase in the permeability of the oblique bedding is 21.4 times that of the vertical bedding and 14.94 times that of the parallel bedding, and under path 2, the increase in the permeability of the oblique bedding is 26.45 times that of the vertical bedding and 142.11 times that of the parallel bedding; the coal samples of the oblique bedding suffer the greatest damage. The increase in the permeability of parallel bedding coal samples, oblique bedding coal samples, and vertical bedding coal samples under path 2 is 1.47 times, 13.96 times, and 11.3 times the increase in the permeability of the corresponding coal samples under path 1, respectively, and the damage produced by coal samples under path 2 is greater than that under path 1.

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“…One of the fatal factors that restrict the effect of acid stimulation is clay breakage and migration. , For example, kaolinite is usually distributed in mesopores (100–1000 nm) or transition pores (10–100 nm) as irregular particles or fragile aggregates attaching to the surface, which are easy to detach and migrate during stimulation, thereby resulting in plugging . In addition, permeability damage caused by the generation and accumulation of fluoride and sellaite precipitations usually occurs when acidizing with HF. , Another critical issue is that coal is a kind of highly stress-sensitive rock. , Numerous experimental results showed that with the increase of effective stress, coal permeability represents an exponent decline. − In addition to the compressibility of the coal matrix, the factor that should be considered important is that the mineral filling also affects coal permeability and fracture compressibility . There are chances that coal seam permeability would decline after demineralization due to fracture compression. , Therefore, insights into the reaction mechanism between acid and rock and how it affects coal stress sensitivity remain to be gained.…”

Section: Introductionmentioning

confidence: 99%

Mechanisms of Acid- and Chelating Agent-Induced Coal Permeability Response Considering the Stress Sensitivity Effect

Chen

Liang

et al. 2022

Energy Fuels

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Chemical stimulation is a promising method for enhancing coalbed methane (CBM) recovery. Since conventional acids may cause formation damage and severe corrosion, this paper investigated the possibility of using GLDA (l-glutamic acid N, N-diacetic acid)a chelating agentand fluoroboric acid (HBF4) as alternatives to HCl. In addition, the stress sensitivity effect of coal during chemical stimulation was considered. A comparative evaluation from the perspectives of mineral dissolution/precipitation, pore structure changes, micromorphology change, and permeability variations with effective stress was done using Qinshui Basin coal samples. The results show that GLDA is preferable for CBM reservoir stimulation. Coal permeability increased 9.73 times and 17.09 times after injecting 2.5 wt % HCl and 5 wt % GLDA, respectively. However, 27% reduction in permeability was reported for the 4 wt % HBF4-acidized coal sample due to fluoride precipitation. With the effective stress increased from 1.5 to 5.5 MPa, the permeability reduction rates of raw coal and HCl-, GLDA-, and HBF4-treated coal samples were 76.92, 39.55, 38.18, and 91.61%, and the stress sensitivity coefficients were 0.374, 0.126, 0.123, and 0.613, respectively. Coal permeability enhancement after GLDA stimulation benefits from increased proportions of seepage pores and macropores and a more unified pore structure. Although HBF4 has a stronger dissolving ability to silicate minerals, it will loosen the coal skeleton, weaken the compressive strength, and then lead to cleat closure. GLDA can decrease fracture compressibility (C f) because of its limitation of dissolving ability, and robust minerals such as quartz and feldspar can be preserved for supporting coal cleats. 5 wt % GLDA at pH = 2 exhibits 0.69 g/m2·h corrosion rate, which is 9.06% of that of HCl. This study shows that GLDA effectively enhances coal permeability and decreases coal stress sensitivity, which provides references for field applications.

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Investigation on effective stress coefficients and stress sensitivity of different water-saturated coals using the response surface method

Cited by 15 publications

References 67 publications

Fractal Apparent Permeability Model for Coal under the Coupling Actions of Stress and Water

Fractal Apparent Permeability Model for Coal under the Coupling Actions of Stress and Water

Experimental Study on the Variation Mechanism of Permeability and Seepage Characteristics of High-Rank Coal with Different Bedding

Mechanisms of Acid- and Chelating Agent-Induced Coal Permeability Response Considering the Stress Sensitivity Effect

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