Enhancing shale gas recovery and CO2 sequestration: Microscopic mechanisms of adsorption and diffusion in shale pores

The global energy imbalance has created significant challenges and environmental consequences. Integrating carbon sequestration with shale gas development provides a promising solution to address both issues simultaneously. This study explores the adsorption, desorption, and diffusion behaviors of methane and CO2 in shale pores using a high-precision, high-pressure adsorption apparatus alongside molecular simulation techniques. Results demonstrate that CO2 shows a markedly higher adsorption capacity in shale pores than methane, particularly at high pressures. Simulations reveal that CO2 molecules nearly saturate pore spaces at pressures above 10 MPa. Methane's diffusion coefficient, initially high at low pressures, drops sharply with increasing pressure, decreasing by approximately 90% from 5.6 x 10(-10) m(2)/s at 154 psi to 1.38 x 10(-11) m(2)/s at 1032 psi. Conversely, CO2 diffusion remains stable under pressure changes, suggesting that methane diffusion is constrained by intermolecular interactions at high pressures, while CO2 retains stable movement. Under a reservoir condition of 30 MPa with adsorbed CH4, CO2 injection at varying pressures continues to enhance CO2 adsorption, underscoring CO2's dual role in boosting shale gas recovery while achieving carbon sequestration. This study highlights CO2-methane displacement mechanisms, providing theoretical insight that support both effective shale gas recovery and CO2 storage.