Numerical simulation study on influence of gangue on coal seam gas drainage

In order to solve problem of reasonable arrangement of gas drainage borehole in coal seam containing gangue, a solid-gas coupling model of gas drainage was deduced with initial and boundary conditions by establishing control equation of coal and rock deformation, control equation of gas migration and evolution equation of porosity and permeability. Distribution laws of gas pressure, permeability and displacement deformation of coal body around single borehole were numerical simulated and analyzed by use of multiphysics field analysis software COMSOL Multiphysics combining with actual geological conditions of IV13 coal seam of a mine. Hole spacing of gas drainage boreholes in coal seam containing gangue was also determined, which provided basis for optimal arrangement of drainage boreholes in coal seam containing gangue. The research results show that during gas drainage process, along with decrease of distance between coal body and borehole, falling range of gas pressure and rising range of permeability of coal body around borehole are the minimum, and displacement of coal body around borehole is the maximum when coal seam contains no gangue; falling range of gas pressure and rising range of permeability of coal body around borehole are the maximum, and displacement of coal body around borehole is the minimum when borehole does not cross gangue.