Impact of coal damage on permeability evolution based on an improved permeability model

Gas-induced deformation during matrix-fracture interaction can cause damage to the microstructure of coal and thus impact the permeability. In this study, A full damage-flow coupling permeability model with geometric equations for the effective matrix-fracture strain was improved. The model was solved by the COMSOL livelink MATLAB program. Then, the impact of the damage effect on the permeability of coal samples with different Young's modulus ratios under uniaxial strain and constant stress conditions was analysed. Damage that occurred first during coal fracture instantaneously accelerated the increase in permeability, while damage that occurred in the matrix slowed the increase in coal permeability. Because the damage ratio increased with increasing Young's modulus ratio, the permeability decreased with increasing Young's modulus ratio. Correspondence between damage and permeability for different Young's modulus ratios was analysed. The improved model was advantageous in solving the problem of mismatch between the theoretical and experimental permeability results. The new model considering the impact of the damage effect was more suitable for the production prediction of CBM production.