Experimental Investigation of Storage Space and Adsorption Capacity Variation of Shale under Different Reaction Times in Supercritical CO 2

Understanding material composition and pore structure variation of shale gas reservoir in the process of supercritical CO 2 (scCO 2 )–brine–shale reaction is of essence to achieve CO 2 sequestration and enhanced natural gas production. In this study, shale sample was saturated with 5% NaCl brine to conduct scCO 2 reaction experiments under 10 MPa and 333 K using a high-pressure batch reactor. Mineralogical composition, element content, surface morphology and gas adsorption features before and after reaction with scCO 2 were measured. According to the results, dissolution of calcite and clay mineral occurred throughout the reaction and carbonate precipitation started as the reaction time exceeded 18 days. The rise of Ca 2+ and K + concentration occurred before 6 days, with moderate increase thereafter. Dissolution enlarged the mesopores and micropores, whereas precipitation only reduced the increasing trend of mesopores, especially for a reaction of 18 days or more. Based on calculations using the CO 2 storage and adsorption potential equation, the storage capacity can be enhanced by 4 to 5 times after reaction, which was predominantly controlled by micropores. Compared to the volumetric enlargement of mesopores, the enhanced micropore uptake was associated with its increased number and volume. Therefore, it is more accurate to evaluate the adsorption capacity based on micropore filling during scCO 2 reaction. Investigating storage space variation and thus understanding the trapping capacity during CO 2 sequestration is a matter of concern for “Carbon Neutrality.”