Numerical simulation study of influencing factors for 3D coal seam gas drainage efficiency

Abstract

Gas drainage from the coal seam can not only decrease gas pressure, content, and gas emission but also prevent gas outburst and explosion; however, the gas drainage efficiency is low. In this study, numerical simulations were conducted on 3D coal seam gas drainage based on the gas–solid–liquid coupling model using COMSOL Multiphysics. The application of different initial conditions of the coal seam on gas drainage showed that the initial permeability, water content, and gas pressure of the coal seam all had influence on gas drainage efficiency. The decreasing velocity of gas pressure in the coal seam accelerated dramatically, and the outburst elimination range where the residual gas pressure decreased below 0.74 MPa increased dramatically at the same time during gas drainage with the increase of the initial permeability. An increase of the water content in the coal seam indicated that the larger the water saturation degree in the coal seam, the more slowly the coal seam gas pressure decreased at the same time and position, and the smaller the outburst elimination range. Moreover, the larger the initial gas pressure, the larger the residual gas pressure, and the more difficult the realization of the regional outburst elimination.