Spatiotemporal evolutions of gas pressures in coal seam during gas extraction under mining disturbance

A 3D geometric model is established based on a fluid‒solid coupling model for purpose of identifying the influences of mining disturbances on the distribution of gas pressures in front of a working face during gas extraction. Then, the stress distribution and gas extraction process are simulated using COMSOL software. The spatiotemporal evolutions of gas pressures in front of the working face are analyzed from the dimensions of point, line, surface, and volume. A comparative analysis has been conducted to explore the distribution patterns of gas pressure in fractures and pores. The results show that under mining disturbance, the stresses in front of the working face create a stress-relaxation area, a stress concentration area, and an original stress area. Moreover, a low stress concentration is located near the boreholes. In the early stage of gas extraction, corresponding to the stress distribution, the gas pressures present a depressurization area, pressure concentration area, and almost undisturbed area. As the time increases after mining, the effects of mining disturbances gradually decrease, and the range of the gas pressure concentration area steadily shortens and shifts toward the front of the working face. Under the same temporal conditions, the gas pressure in pores is higher than that in fractures. At the onset of mining, the pore gas pressure is even greater than the initial pressure. Furthermore, during the identical extraction period, the "concentration area" of pore gas pressure is situated farther away from the coal wall of the working face compared to the "concentration area" of fracture gas pressure. These results of the study provide theoretical support for arranging drainage boreholes, enhancing gas extraction efficiency, safeguarding against gas accidents.