Optimization of Accurate Spacing for Gas Extraction from Damaged Coal Seams Based on a Dual-Penetration Model

In order to develop precise hole placement technology for gas extraction, this paper combines industrial testing, the evolution law of coal rock damage permeability, and the coal double-pore double-permeability model; establishes a coupling model of the coal damage deformation field and matrix-fracture double diffusion seepage field; and determines precise hole placement spacing for a coal seam gas by using the COMSOL Multiphysics 5.6 numerical simulation software. This study shows that the effective radius of gas extraction is 4.8 m after 180 d of extraction, which is a power function of the extraction time. The permeability of the coal body is affected by matrix adsorption, and contraction and effective stress, and the influence range between the boreholes under multi-hole extraction increases with the increase in spacing; at the same time, we took into account the positive effect of the permeability change on the extraction effect and ultimately determined the optimal spacing of boreholes in Dashucun Mine to be 6 m, which was arranged in the square area. The extraction effect was good after the on-site test, and the results of this study can provide guidance for the optimal arrangement of the spacing of boreholes in the underground areas of coal mines.