Investigation of adsorption kinetics of CH4 and CO2 on shale exposure to supercritical CO2

The adsorption kinetics behaviors of CH4 and CO2 on shale are closely related to CO2 sequestration and enhanced shale gas recovery (CS-ESGR). To investigate the influence of supercritical CO2 (ScCO2) exposure on adsorption kinetics behaviors of CH4 and CO2 on shale, X-ray diffraction analysis, low-pressure N2 adsorption and adsorption kinetics experiment of CH4 and CO2 were conducted on raw and ScCO2-treated (10 day/16MPa/40 °C) shale collected from the Ordos Basin. Adsorption rates of CH4 and CO2 by shale were fitted by different adsorption kinetics models, and results indicate that Bangham adsorption (BA) model exhibits a better fitting effect (R2＞0.99) than Pseudo-first-order (PFO) and Pseudo-second-order (PSO) kinetic model and Elovich adsorption (EA) model. After ScCO2 exposure, the adsorption rate of CH4 and CO2 by shale decreased, which may be mainly caused by the decrease of high energy adsorption sites of shale. In addition, the adsorption rate of CO2 by shale is significantly higher than that of CH4, and the influence of pressure on the adsorption rates of CH4 and CO2 is remarkably different, suggesting that the CS-ESGR project should be divided into three stages: Fracturing-Recovery, Replacement-Recovery-Sequestration, and Replacement-Sequestration-Recovery. This study provides a reference for future optimization design of CS-ESGR. [Display omitted] •Adsorption kinetics behaviors of CH4 and CO2 on shale exposure to ScCO2 were studied.•Adsorption rates of CH4 and CO2 on shale were fitted by different kinetics models.•Adsorption rates of CH4 and CO2 by shale decreased after ScCO2 exposure.•Multiple factors influencing the adsorption rate of CH4 and CO2 were studied.•The CS-ESGR project is preliminarily suggested to be divided into three stages.