Study on Gas Drainage Characteristics Based on Permeability Anisotropy of Coal

To determine the effective drainage area, a fluid-solid coupling model of gas-bearing coal rock mass is established, and the geometric model is established using COMSOL Multiphysics software for numerical solution. On the basis of considering the permeability anisotropy, the variation law of gas pressure in different positions around the borehole is studied. The results show that the gas pressure contour map presents an elliptical shape after considering the permeability anisotropy. The permeability anisotropy affects the gas migration in coal. The lower the permeability is, the slower the gas moves in the coal seam. The Darcy velocity is proportional to the permeability, i.e. the Darcy velocity increases with the increase of permeability. The permeability anisotropy makes Darcy velocity contours around boreholes elliptically distributed. The closer to the center of the borehole is, the higher the speed of Darcy velocity is, and the maximum Darcy velocity decreases with the increase of time. When the gas pressure around the drilling hole reaches 0.74 MPa, the effective extraction area of the borehole shows the distribution of large left-right and small upper-lower under the influence of permeability anisotropy. The gas is difficult to be extracted in the place with low permeability.