A fluid-solid coupling model of coal seam gas considering gas multi-mechanism flow and a numerical simulation analysis of gas drainage

In order to better reveal the nature and law of gas migration in soft and low permeability coal seams during gas drainage, based on the dual medium of pore and fracture, a coupled fluid-solid model of gas multi-mechanism considering the influence of effective stress, multi-mechanism flow of coal seam gas, real gas effect and tortuosity is established. With the No. 13181 working face of the Baiping Mine Coal Industry Co.,Ltd. of Zhengzhou Coal Group Industry(Henan) as the engineering background, the COMSOL software is used to carry out a numerical simulation of gas drainage based on the model established. The dynamic distribution law of gas pressure with the drainage time is fully analyzed, and the accuracy of the effective drainage radius of the numerical simulation is verified in combination with the on-site measurement results. Numerical simulations of gas drainage without considering the Klinkenberg effect, matrix gas diffusion and multi-mechanism flow of coal seam gas are carried out systematically, and the specific effects of different control factors on coal seam gas migration are compared and analyzed. The results show that the gas pressure of coal seam is elliptic with the center of the drainage hole after the drainage. The variation range of coal seam gas pressure and effective drainage radius gradually decreases with the drainage time and tends to be stable. The average error between the numerical simulation results and the on-site measurement results of effective drainage radius of coal seam gas is 3.65%,which verifies the effectiveness and rationality of the coupled fluid-solid model of coal seam gas multi-mechanism. Compared with the simulation results considering the effect of multi-mechanism flow of coal seam gas, the effective drainage radius and permeability without considering the Klinkenberg effect is smaller, while the effective drainage radius and permeability without considering the matrix gas diffusion and multi-mechanism flow are obviously larger, indicating that the Klinkenberg effect and matrix gas diffusion can promote and inhibit the coal seam gas flow respectively.