Analysis of coupled gas flow and deformation process with desorption and Klinkenberg effects in coal seams

Coupled gas flow and solid deformation in porous media has received considerable attention because of its importance in pneumatic test analysis, contaminant transport, and gas outbursts during coal mining. Gas flow in porous media is quite different from liquid flow due to the large gas compressibility and pressure-dependent effective permeability. The dependence of gas pressure and gas desorption on gas permeability has a significant effect on gas flow, but has been ignored in most previous studies. Moreover, solid deformation has a direct impact on the porosity, which also leads to desorption or sorption of methane in the coal seam. In this study, a coupled mathematical model for solid deformation and gas flow is proposed and is implemented using a finite element method. The numerical code is used to solve the gas flow equation with Klinkenberg effect, and is validated by comparison with available analytical solutions. Then, it is used to simulate the coupled process during gas migration in a deformable coal seam. The numerical results indicate that the desorption and Klinkenberg effects and mechanical process effect make a significant contribution to gas flow in the coal seam. Without considering the desorption and Klinkenberg effects and the coupling action of mechanical process, the gas pressure in the coal seam would be underestimated.