Coalbed methane (CBM) is the very important unconventional energy resource. Enhancing extraction is the main method to improve the utilization of CBM and prevent coal mine gas disasters. To reveal the laws of gas migration during the underground gas extraction, the paper established the solid‐gas coupling model, regarding coal as the homogeneous elastic medium with dual pore‐fracture structure and dual permeability and considering the gas dynamic diffusion coefficient. Then, the regulations of gas migration in the in‐seam borehole were simulated by the COMSOL Multiphysics software and verified via the field trials of gas extraction. The results revealed that the permeability increased with time due to the coupling of matrix shrinkage and volume compression of coal, in which the matrix shrinkage played a leading role. The gas seepage velocity at the observation points can be divided into three stages: the rapid rise stage, the stable decline stage, and the stable and invariant stage. The gas extraction rate continued decreasing with time and finally tended to a fixed value. In the coal seam #4 of Zhongxing coal mine, the measured flow rates of three in‐seam drilling holes were in good agreement with the simulation results, which verified the correctness of the theoretical coupling model.

The thick and hard rock strata (THRS) exist widely in coal measure strata, which control the movements of overlying rock strata in stopes. When THRS break, great energy is released, which could aggravate the risks of coal and gas outburst, rock burst, and other dynamic disasters. Therefore, the foundation and key of preventing dynamic disasters are to distinguish the THRS that could induce coal-rock dynamic disasters and to analyze the laws of rock stratum breaking and energy releasing. The paper proposed the theoretical calculation methods of the energy accumulation and attenuation of rock breaking which is greatly affected by the hanging length of rock strata and the spreading distance. One or more roof strata that play a leading role in inducing dynamic disasters of the underlying coal mass are defined as the key disaster-inducing strata (KDIS). The disaster-inducing coefficient (DIC) is defined and used as the criterion of KDIS. The greater the source energy, the shorter the spreading distance, and the smaller the attenuation coefficient are, the easier the roof strata are to become KDIS. The disaster-inducing ability of the main THRS was analyzed, and the igneous sill was judged as KDIS, taking the Yangliu Coal Mine as project background. The breaking laws of the igneous sill were obtained by the methods of UDEC numerical simulation and microseismic monitoring, which verified the criterion of KDIS.

Coalbed methane (CBM), which is extremely rich in deep coal reserves in China, is not only the material cause of gas explosion and coal-gas outburst disasters but also a clean and environmentally friendly energy source. Gas drainage must be carried out during deep coal mining to avoid gas accidents while obtaining clean energy. The low-level roadway is an effective gas drainage measure for coal seams with high coal-gas outburst risk and low-permeability, and it can simultaneously realize the functions of gas drainage before and during mining. Roadway tunneling has a strong influence on the stress and permeability properties of the adjusted coal seams, and further determines the gas drainage efficiency and the layout of the air-return roadway. Taking the Pingshu Coal Mine as an example, this paper analyzes the influence of the vertical distance between the low-level roadway and the underlying coal seam, and the influence of the width and height of the low-level roadway on the stress relief and deformation characteristics. The results indicate that the low-level roadway tunneling results in a nonuniform stress disturbance of coal seam #15. And a reasonable layout and size parameters of the air-return roadway in coal seam #15 were proposed based on which gas drainage practices were carried out with good effects in panel #15211. The research can effectively guide the elimination of coal and gas outburst in return air roadway, and achieve the purpose of safe and rapid tunneling coal roadway under the environment of highly-gassy coal seam.

The thick-hard rock strata (THRS) are widely distributed among coal-bearing strata. In the process of coal mining, the strong dynamic load will be produced after the THRS are broken, which will lead to dynamic disasters such as mine earthquake, rock burst and so on. Therefore, revealing the breaking law of THRS is helpful to prevent and control the dynamic disasters. This paper constructed the mechanical model of THRS based on thick plate theory and obtained the breaking distance of THRS, which is applied to Yangliu Coal Mine. And we constructed the numerical stratigraphic model and analyzed the caving characteristics, the changing rules of displacement and stress of THRS under different advancing distances. Then the above results are verified by the change of hydraulic support resistance. The research shows that the critical instability distance of THRS overlying the coal seam #10 in Yangliu Coal Mine was 296.4 m. Based on the numerical simulation, the displacement and stress of the main THRS increased greatly at the position of 250-300 m, and occurred a large-scale collapse. The hydraulic support resistance of the working face increased sharply and microseismic energy is released rapidly when the mining reached about 330 m, the reliability of the theoretical analysis and numerical simulation were verified by the engineering tests.