Enhanced Modeling of CO₂ Adsorption on Shale: Incorporating Volumetric Effects for Accurate Isotherm Predictions

Accurate prediction of CO2 adsorption isotherms on shale is essential for precisely assessing the CO2 storage capacity of different shale reservoirs. Using the volumetric method, subcritical and supercritical CO2 adsorption isotherms on four different shale samples were measured at temperatures of 308.15, 318.15, and 328.15 K. Recognizing that adsorption-induced swelling of the shale matrix can significantly affect adsorption behavior, we developed three modified adsorption models that account for volumetric changes: modified–Langmuir (M–L), modified Dubinin–Radushkevich (M-D–R), and Dubinin–Astakhov (M-D–A). The findings reveal that the CO2 adsorption capacity estimated by the three modified models is more accurate and reasonable than that of the original models when applied to fit the experimental data. Among them, the M-D–A model provides the most accurate prediction of excess adsorption when incorporating the volume change effect caused by adsorption-induced swelling and offers extensive insight into subcritical and supercritical CO2 adsorption behavior.