Apparent Permeability Mechanisms of Shale Gas Considering Adsorption Deformation and Slippage Effects

The efficient development of shale gas resources constitutes a critical strategic contribution in promoting the transition toward sustainable energy systems worldwide. It is essential for improving the security and dependability of the world’s energy supplies. However, the microscopic pore structure of shale is complex and diverse, and the quantitative influence of mechanical deformation of pore structures on seepage paths has not yet been fully characterized. Consequently, an accurate prediction of the development of gas’s permeability in shale reservoirs is therefore essential for advancing energy development strategies. In this study, the Simplified Local Density (SLD) theoretical framework was employed to model gas adsorption phenomena within shale formations. Based on this methodological approach, a model describing adsorption-induced deformation in shale gas reservoirs was developed by correlating changes in surface energy due to gas adsorption with corresponding mechanical strain. A porosity equation that incorporated both adsorption-induced swelling and effective stress effects was subsequently obtained. Based on cubic law, a shale gas seepage model was proposed that integrated the gas slippage effect into a permeability structure. Furthermore, by correlating the slip coefficient with absolute permeability, the influences of adsorption-induced swelling and volumetric strain on both the first-order and second-order dynamic slip coefficients were quantitatively evaluated. To validate the model, published experimental data on shale gas’s adsorption and permeability under varying boundary conditions were utilized to analyze adsorption deformation characteristics and associated seepage behavior. Furthermore, based on the model, the main controlling coefficients governing permeability variations during shale gas’s extraction were investigated, along with the dynamic changes in the slip coefficient under different influencing parameters. The findings from this study provide a theoretical basis for evaluating the production capacity of shale gas reservoirs, thereby enhancing development efficiency.