Study on the influence of roof and floor rock permeability on gas extraction in coal seam

In order to investigate the influence of roof and floor rock properties on gas drainage, based on the fluid-solid coupling equation of coal containing gas, by using COMSOL multiphysics software, the numerical simulation of gas drainage from drilling for both breathable and impermeable roof and floor strata was carried out, the porosity of the permeable roof and floor rock was set as 20%, and that of the impermeable roof and floor rock was set as 0. The results show that the gas always flows along the drilling in the process of drainage under different roof and floor rock properties, but the roof and floor rock properties have obvious influence on the gas flow field; the longer the gas extraction time under different roof and floor properties, the greater the influence range of drilling, at the same time, the farther away from the center of the drilling, the greater the residual gas content in the coal seam, but the gas pressure of the breathable rock model decreases faster and the residual gas pressure is lower; the roof and floor rock properties have a significant impact on the effective range of coal seam gas drainage, compared with the impermeable rock, the effective range of drilling in the breathable rock is larger. The research results have a certain significance for guiding the gas drainage of drilling passed through coal seam.