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

Abstract

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.