Abstract: To study gas(methane) transport mechanism during the drilling drainage process from coal seams, the deformation of coal in different areas around drilling boreholes and the dynamic change in the permeability were discussed, and coal gas flow coupling equations were deduced for both relief zone and non-distressed zone around drilling boreholes.A geometric model was established according to the coal seam's physical parameters of 15-31010 working face of a mine, then the equations were solved by using COMSOL Multiphysics finite element analysis software. The coupling relations between coal deformation, the dynamic penetration and gas pressure around drilling were analyzed on the basis of the simulation results. The simulation results were verified for the related parameters by drainage effects in field. The results show that during the gas drainage process, coal gas pressure gradually decreases over time,that the gas pressure in relief zone increases significantly along the center of a drilling borehole and the growth rate of gas pressure in non-distressed zone gradually slowes down and eventually tends to be stabilized,that the permeability follows is a“V”-shape pattern of variation around drilling boreholes,that the coal deformation in relief zone is larger than that in non-distressed and there is a negative correlation between the deformation of coal and the distance of the measuring point from the borehole.The simulation results conform basically with the reality.

Key words: gas drainage, coupling model, numerical simulation, permeability, pressure relief