An anisotropic coal permeability model that considers mining-induced stress evolution, microfracture propagation and gas sorption-desorption effects

Zhang, Zetian; Zhang, Ru; Xie, Heping; Gao, Mingzhong; Zha, Ersheng; Jia, Zheqiang

doi:10.1016/j.jngse.2017.08.028

Cited by 44 publications

(20 citation statements)

References 56 publications

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“…Then, they carried out experimental verification on their damage‐induced permeability model. Zhang et al used the change in radius of the microfracture to describe the damage variables and then achieved their model validation. In order to avoid the description of damage variables, Chen et al believed that the damage‐induced permeability should be modified by a coefficient, which was exponential to the deviatoric stress.…”

Section: Introductionmentioning

confidence: 99%

Damage‐induced permeability model of coal and its application to gas predrainage in combination of soft coal and hard coal

Zhang

et al. 2019

Energy Science & Engineering

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Coal permeability is a key parameter that affects the drainage of coal bed methane (CBM). Owing to the lower original permeability of coal seams in China, more attention was paid to the study of damage‐induced permeability laws. However, the theory of damage‐induced permeability still needs to be improved. In this paper, the permeability evolution experiments during the complete stress–strain process of coal were carried out firstly. The results are shown that with the increase in axial strain, the coal permeability decreases slowly at first, then increases rapidly, and finally increases slowly or even remains unchanged, and the peak stress point can be regarded as the extreme point of permeability. Then, the equivalent plastic strain was used to describe the damage of coal. Based on the above results, a new damage‐induced permeability model was developed, and the new model can match the experimental data of permeability very well. In addition, solid–gas coupling models of coal were developed based on the new permeability model, and the numerical results show that there is a region of sudden increase in permeability around the borehole where plastic failure occurs, which indicates that the damage‐induced permeability model is reasonable. Finally, the results of numerical simulation of gas predrainage in combination of soft coal and hard coal under different cases were used to optimize the borehole layout of gas predrainage in the field.

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Section: Introductionmentioning

confidence: 99%

Damage‐induced permeability model of coal and its application to gas predrainage in combination of soft coal and hard coal

Zhang

et al. 2019

Energy Science & Engineering

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“…The coal matrix is also usually simplified to shape of cubes. Therefore, the mechanical properties of coal are considered to be nearly orthotropic [48].…”

Section: Orthogonal Anisotropic Coal Under True Triaxial Stressmentioning

confidence: 99%

A Statistical Damage Constitutive Model of Anisotropic Rock: Development and Validation

et al. 2021

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The damage constitutive model is of great significance to research the stress-strain relationship and damage evolution of rock under loading in engineering. In order to investigate the effect of anisotropic characteristic on the stress-strain relationship and damage evolution, a statistical damage constitutive model of anisotropic rock under true triaxial condition was developed. In this study, the plane which existed perpendicular to the coordinate axis was extracted from representative volume element (RVE) of rock. The extracted plane was assumed to be composed of abundant mesoscopic elements whose failure strength satisfied the Weibull distribution. According to the number of failure elements on the plane in each direction under loading, the anisotropic damage variable was established based on the proposed concept of areal damage. A statistical damage constitutive model of anisotropic rock was developed by using strain equivalent hypothesis and generalized Hooke constitutive model. Subsequently, the parameters in the anisotropic damage constitutive model were determined by the method of total differential. Thus, the damage evolution of anisotropic rock under various stress conditions can be conveniently evaluated by the anisotropic damage model. The model was validated based on the tests of rocks under the stress conditions of conventional triaxial and true triaxial, respectively. Moreover, for the purpose of studying the influence of parameters on the model, sensitivity analyses of mechanical parameters and model parameters were carried out. The results of statistical damage constitutive clearly demonstrate the stress-strain and damage evolution of anisotropic rock under various stress conditions.

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“…The porosity of the coal matrix and fracture can be respectively expressed as follows (Fan et al, 2016;Liu et al, 2017;Zhang et al, 2017).…”

Section: ‹ Mass Conservation Equations Of Water and Methane In The Hymentioning

confidence: 99%

“…The porosity of the coal matrix and fracture can be respectively expressed as follows (Fan et al., 2016; Liu et al., 2017; Zhang et al., 2017). where φm is the porosity of the coal matrix; S=εv+pm/Ks−εs; S0=εv0+pm0/Ks−εs0; K s is the volume modulus of the coal skeleton; αm is the Biot-effective stress coefficient corresponding to the pore; φf is the porosity of the fracture; εs is the skeleton strain caused by the adsorbed methane; εv is the volume strain of coal, and εv=εx+εy+ε…”

Section: Mathematical Model Of the Methane Driven By Hydraulic Fractumentioning

confidence: 99%

Mathematical model of methane driven by hydraulic fracturing in gassy coal seams

Huang

2020

Adsorption Science & Technology

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During hydraulic fracturing in gassy coal, methane is driven by hydraulic fracturing. However, its mathematical model has not been established yet. Based on the theory of ‘dual-porosity and dual-permeability’ fluid seepage, a mathematical model is established, with the cleat structure, main hydraulic fracture and methane driven by hydraulic fracturing considered simultaneously. With the help of the COMSOL Multiphysics software, the numerical solution of the mathematical model is obtained. In addition, the space–time rules of water and methane saturation, pore pressure and its gradient are obtained. It is concluded that (1) along the direction of the methane driven by hydraulic fracturing, the pore pressure at the cleat demonstrates a trend of first decreasing and later increasing. The pore pressure gradient exhibits certain regional characteristics along the direction of the methane driven by hydraulic fracturing. (2) Along the direction of the methane driven by hydraulic fracturing, the water saturation exhibits a decreasing trend; however, near the cleat or hydraulic fracture, the water saturation first increases and later decreases. The water saturation in the central region of the coal matrix block is smaller than that of its surrounding region, while the saturation of water in the entire matrix block is greater than that in the cleat or hydraulic fracture surrounding the matrix block. The water saturation at the same space point increases gradually with the time progression. The space–time distribution rules of methane saturation are contrary to those of the water saturation. (3) The free methane driven by hydraulic fracturing includes the original free methane and the free methane desorbed from the adsorption methane. The reduction rate of the adsorption methane is larger than that of free methane.

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An anisotropic coal permeability model that considers mining-induced stress evolution, microfracture propagation and gas sorption-desorption effects

Cited by 44 publications

References 56 publications

Damage‐induced permeability model of coal and its application to gas predrainage in combination of soft coal and hard coal

Damage‐induced permeability model of coal and its application to gas predrainage in combination of soft coal and hard coal

A Statistical Damage Constitutive Model of Anisotropic Rock: Development and Validation

Mathematical model of methane driven by hydraulic fracturing in gassy coal seams

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