Influences of matrix-fracture interaction on permeability evolution: considering matrix deformation and stress correction

Studying the permeability of coal seam is of guiding significance for the applicability and feasibility of rational mining of coalbed methane and other energy sources. A large number of current permeability models are established based on the elastic and adsorption strains. However, these models often treat the matrix as a rigid body and assume that the adsorption deformation is fully regulated by the fracture aperture when considering these two strains. The matrix deformation is neglected in predicting permeability, and the effect of adsorption swelling is also overestimated. Therefore, a new permeability model is proposed to predict reservoir permeability under different boundary conditions. The model proposes an internal expansion coefficient f to correct the effects of matrix adsorption on fracture aperture and external stress, and considers the deformation behavior of the fracture and matrix under the effective stress. To compare the effects of matrix deformation and stress correction on permeability, the three models for permeability under different boundary conditions are validated through the field data and laboratory data by comparing the model without considering stress correction and the model without considering the deformation of the matrix itself. The results show that the stress correction has a more significant effect on the permeability evolution under uniaxial strain, and that the model without consideration of both the stress correction and the deformation of the matrix will obtain higher internal expansion coefficient f. Finally, the proposed model is further compared with four classical models to illustrate again its superiority.