Abstract:In order to improve the effect of gas drainage in low permeability coal seams, the pressure relief and permeability enhancement effect of low permeability coal seams was studied by using the hydraulic large-diameter graded hole making technology. Through the stress balance equation, gas seepage equation and coupling equation of coal, the process of gas adsorption, desorption, seepage and the coupling relationship with stress in coal are analyzed. By using COMSOL Multiphysics software, a three-dimensional calculation model of pumping and hole making with zero permeability boundary is constructed, and the pressure relief pumping effect under different pumping time and different hole making radius (0.3m, 0.6m, 0.9m) is studied. The research shows that the gas pressure around the borehole decreases with the continuous gas drainage after the coal seam cave is built. With the gradual increase of the drainage time, the gas pressure reduction area expands gradually, and the pressure relief range increases continuously. The gas pressure drop speed of the hole cavity model with a radius of 0.9m is more obvious, which can relieve the pressure and increase the permeability of the coal seam in a shorter time to achieve the coal seam outburst elimination.
