Fracture is the primary channel of gas seepage in coal seams and controls the drainage efficiency of coal bed methane (CBM). However, the seepage characteristics and dynamic evolution law in the fractures of gas-bearing coal under external loads are yet to be clearly revealed. In this study, an industrial computer tomography (CT) scanner equipped with a triaxial loading system was used to conduct gas-seepage and CT scanning experiments under triaxial compression conditions. The results showed that the fracture volume and permeability decreased first and then increased during the complete stress–strain process of gas-bearing coal, displaying an approximate U-shaped variation trend involving a decrease stage, an increase stage, and a jump-increase stage. The lattice Boltzmann method (LBM) was applied to make the seepage processes of gas-bearing coal reappear, and a modified nonlinear permeability model was developed to represent non-Darcy seepage inside fractured coal. The LBM simulation results mirrored the dynamic evolution of the gas seepage field and gas permeability controlled by fracture propagation. The proposed modified nonlinear permeability model effectively reflected the nonlinear variation behaviour of gas permeability and was superior to the traditional Darcy's model in describing nonlinear seepage of gas-bearing coal.

裂缝是煤层瓦斯渗流的主要通道，控制着煤层气（CBM）的抽采效率。然而，外载作用下含气煤裂缝的渗流特征和动态演化规律尚有待明确揭示。在这项研究中，使用配备三轴加载系统的工业计算机断层扫描 (CT) 扫描仪在三轴压缩条件下进行气体渗漏和 CT 扫描实验。结果表明，在含气煤的完整应力-应变过程中，裂缝体积和渗透率先下降后上升，呈现出下降阶段、上升阶段和跳跃上升阶段的近似U型变化趋势。 . 应用格子玻尔兹曼方法（LBM）再现了含气煤的渗流过程，建立了改进的非线性渗透率模型来表示裂隙煤内部的非达西渗流。LBM模拟结果反映了裂缝扩展控制的气体渗流场和气体渗透率的动态演变。提出的修正非线性渗透率模型有效地反映了瓦斯渗透率的非线性变化行为，在描述含气煤非线性渗流方面优于传统的达西模型。