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.

Coalbed methane (CBM) is not only the material cause of gas explosion and coal-gas outburst disasters during underground coal mining, but also a kind of clean energy. Coal permeability is an important parameter for CBM drainage. Although many coal permeability models have been developed in the past decades to describe the permeability evolution characteristics under elastic state, few of them could explain the permeability behavior of the mining-disturbed coal which is often the situation of CBM drainage during underground coal mining. The paper analyzed the mechanical factors affecting the damage-permeability characteristics of mining-disturbed coal, proposed the concept of the deviatoric stress ratio (DSR), and then established the statistical damage and permeability evolution models based on DSR. Results show that the deformation and damage of coal is controlled by the deviatoric stress and minimum principal stress. The plastic damage degree of coal mass becomes more serious with DSR increase, which leads to the improvement in permeability. The damage constitutive model was established based on the Weibull distribution function and DSR, and then the permeability model of mining-disturbed coal was built combining the Kozeny-Carman equation. The acoustic emission (AE) and permeability experiments of the loading and unloading coal sample were conducted. After normalizing and fitting the accumulative AE counts, the damage and permeability evolutions with respect to DSR were found out. The model-predicted permeability could match with the experiment results, verifying the reliability of the theoretical permeability model. The purpose of this paper is to provide a new approach for modeling damage and permeability of mining-disturbed coal based on DSR.