Coupling Mechanism of CO₂ Adsorption and Pore Deformation in Shale Kerogen with Different Maturities

The adsorption of CO₂ in shale kerogen results in the pore deformation, which, in turn, affects the adsorption capacity of kerogen. The coupling characteristics and micro-mechanisms between CO₂ adsorption and pore deformation in shale kerogen remain unclear. For kerogen with different maturities, this study systematically simulated CO₂ adsorption behavior under various strains and pressures using molecular simulation methods. Building on this, the coupling coefficient between CO₂ adsorption and pore deformation in shale kerogen was quantified through poromechanical theory, uncovering its dynamic volution with kerogen maturity. Additionally, the micro-mechanisms of adsorption-deformation coupling were clarified by examining the evolution of kerogen pore structures and their non-bonded interactions (e.g., van der Waals and electrostatic forces) with CO₂. The findings show that the coupling coefficient between CO₂ adsorption and pore deformation in shale kerogen is maturity-dependent, and results derived from coal organic matter are not directly transferable. Furthermore, the adsorption-deformation capacity of kerogen diminishes as maturity increases. The coupling coefficient is approximately constant within a certain pressure range (>2 MPa), and significant differences are observed in the coupling coefficients for immature kerogen during its compression and expansion stages. The adsorption interaction of CO₂ on kerogen is mainly controlled by van der Waals forces, followed by electrostatic forces. The adsorption of CO₂ increases the porosity and specific surface area of kerogen and induces a shift towards larger pore sizes in the pore size distribution. The results reveal the coupled characteristics and micro-mechanisms between CO₂ adsorption and pore deformation in shale kerogen, which provide theoretical guidance for evaluating the performance of CO₂ sequestration in shale reservoirs.