Research on the Dynamic Apparent Permeability of Shale: Coupling Anisotropic Deformation Characteristics and Multiple Transport Mechanisms

As shale gas is an unconventional energy source, it is believed to be essential for achieving green resource development and improving the energy supply-demand balance. However, owing to shale's substantial anisotropic properties and various microstructures, its gas flow characteristics and transport mechanisms are exceedingly complex. Therefore, accurately predicting gas permeability evolution in shale pores was considered to be important for energy development. In this study, an examination of the apparent volumetric strain, caused by the synergistic effects of effective stress and gas adsorption, combined with analysis of dynamic changes in pores in different directions has been undertaken. Based on the Knudsen number (<i>K</i>_n), gas flow mechanisms in shale were separated further to create an anisotropic apparent permeability model. The model was validated by publicly available experimental data concerning the permeability under different stress conditions. The influence of different flow regimes and mechanisms on permeability changes during shale reservoir development has been discussed and analyzed with a model parameter sensitivity analysis being carried out. The results demonstrated that if both mechanisms (effective stress and gas adsorption) were ignored, the shale permeability would be underestimated; however, if shale's anisotropic mechanical properties were ignored, the apparent permeability would be overestimated. Our findings could provide theoretical guidance for energy exploitation, which would be beneficial in contributing to sustained and rapid energy development.