Fluid-solid coupling dynamic equations considering gas desorption contraction and coal motion deformations

The coals are assumed as isotropic homogeneous saturated porous media, dynamic characteristics of porosity and permeability of coals and coal deformation caused by gas desorption are all considered, gas seepage equations about porosity, permeability and desorption contraction deformation are built based on Darcy's law, and fluid-solid coupling equations for gas seepage are finally built, which are composed of the above-mentioned dynamic balance differential equations and gas seepage equations. In the end, one horizontal gas drainage hole is taken as a computational example, the gas pressures calculated by the new model built in this paper are compared with those by the normal model that does not include gas adsorption and motion deformation of coals, the new model is proved to be reasonable based on the mechanism of desorption contraction and seepage, and the characteristics of permeability, gas pressure and radial displacements around the hole are analyzed based on the new model.