Numerical Analysis and Prediction of Coal Mine Methane Drainage Based on Gas–Solid Coupling Model

Abstract

Methane drainage using boreholes is one of the most effective means of preventing coal mine methane disasters. However, the distributions of stress and permeability around the borehole and the effective influence radius of methane drainage are not clearly known. To solve this problem, a mathematical model of gas-solid coupling of coal rock was first established in this study based on the Kozeny-Carman equation. In this model, the coal rock was considered as a fracture-porosity dual medium. Methane's flow was seepage in the fracture system and diffused in the pore system. Second, the finite volume method was used to discretize the coupling model. The Newton-Raphson iteration and generalized minimal residual algorithm method were used to solve the nonlinear coupling equation after diffusion. Finally, Fortran language was used to simulate the process of methane drainage using a borehole. Results showed that there was respectively stress concentration on the left and right sides of the borehole. This area was associated with the lower permeability in these zones and destroyed the borehole, which is the one of the main reasons for the low efficiency of methane drainage. The relationship between the effective influence radius and the drainage time could be described by a power function. The effective influence radius of the borehole, cumulative methane drainage volume, and residual methane content distribution obtained by simulation were well consistent with the data obtained by the actual measurements, which proves the credibility of the gas-solid coupling and solving methods. This study provides some theoretical reference for methane drainage and the solution of multi-physics field coupling model in coal mines.