Anisotropy is a very typical observation in the intrinsic bedding structure of coal. To study the influence of anisotropy of coal structure and stress state on the evolution of permeability, a newly developed multifunctional true triaxial geophysical apparatus was used to carry out mechanical and seepage experiments on bedded coal. The permeability and deformation of three orthogonal directions in cubic coal samples were collected under true triaxial stress. It has detected the significant permeability anisotropy, and the anisotropy is firmly determined by the bedding direction and stress state of coal. Based on the true triaxial mechanical and seepage test results, the coal with bedding was simplified to be represented by a cubic model, and the dynamic anisotropic (D-A) permeability model was derived by considering the influence of bedding and stress state. The rationality of the permeability model was verified by the experimental data. Comparing the permeability model with Wang and Zang (W–Z) model, Cui and Bustin (C–B) model and Shi and Durucan (S–D) model, it is found that the theoretical calculated values of the D-A permeability model are in better agreement with the experimental measured values, reflecting the superiority of the D-A permeability model. Based on incorporating the model of D-A permeability under the concept of multiphysics field coupling, the numerical simulation experiments of coal seam gas extraction with different initial permeability anisotropic ratios were carried out by using COMSOL multiphysics simulator. The influence of initial permeability anisotropy ratio on gas pressure distribution in coal seam during gas extraction was explored, which provides theoretical guidance for the optimization of borehole layout for gas extraction in coal mine.

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真三轴应力下层状煤渗透率各向异性研究及应用

各向异性是煤固有层理结构中非常典型的观察结果。为研究煤结构各向异性和应力状态对渗透率演化的影响，利用新研制的多功能真三轴地球物理仪对层状煤进行力学和渗流实验。收集立方煤样在真三轴应力下三个正交方向的渗透率和变形情况。检测到显着的渗透率各向异性，各向异性由煤层的层理方向和应力状态确定。根据真三轴力学和渗流试验结果，将带层理的煤简化为立方模型，考虑层理和应力状态的影响，推导出动态各向异性（DA）渗透率模型。实验数据验证了渗透率模型的合理性。将渗透率模型与 Wang and Zang (W-Z) 模型、Cui and Bustin (C-B) 模型和 Shi and Durucan (S-D) 模型进行比较，发现 DA 渗透率模型的理论计算值在与实验测量值吻合较好，体现了DA渗透率模型的优越性。基于多物理场耦合概念下的DA渗透率模型，利用COMSOL多物理场模拟器对不同初始渗透率各向异性比的煤层气抽采进行数值模拟实验。