Gas solid coupling model based on orthogonal anisotropy characteristic of coal and its application

Abstract

In order to describe the permeability evolution law in the coupling process of anisotropic coal seam and gas, based on the assumption that the coal structure is orthogonal anisotropic, the orthogonal anisotropic permeability model was established by using the superposition relationship of coal deformation under the adsorption effect, and the gas solid coupling model considering the orthogonal anisotropic characteristics of coal was further deduced. The model was used to analyze the law of permeability under different adsorption pressures of Ⅱ1 coal seam in Jiulishan Mine and the influence of borehole dip angle of 4# coal seam in Tingnan Mine on pumping effect. The results show that under the same confining pressure, the permeability of face cleat, butt cleat and vertical bedding decreases gradually with the increase of gas pressure, which is consistent with the experimental results. The average relative errors of permeability simulation results and test results in the directions of surface cleat, butt cleat and vertical bedding are 2.55 %, 14.19 % and 4.26 %, respectively. The gas drainage volume increases with the increase of borehole dip angle. In the design of borehole drainage, increasing the angle between borehole and coal seam bedding plane can improve the gas drainage volume.

Keywords

• orthogonal anisotropy
• anisotropic structure ratio
• permeability equation
• gas solid coupling
• gas drainage