Effect of the Water Content on the Adsorption of CO 2 and CH 4 in Calcite Slit Nanopores: Insights from GCMC, MD, and DFT.

It is significant to understand the adsorption mechanisms of shale gas (CH 4 ) and CO 2 in shale formations to enhance CH 4 recovery rates and enable geological CO 2 storage. This study provides a comprehensive investigation into the adsorption behaviors of CO 2 and CH 4 within dry and hydrous calcite nanopores, utilizing a combination of grand canonical Monte Carlo simulations, molecular dynamics simulations, and density functional theory calculations. In dry calcite slits, the calculated results for the adsorption capacity, density profile, and isosteric heat of CO 2 and CH 4 reveal that CO 2 possesses a stronger adsorption affinity, making it preferentially adsorb on the pore surface compared to CH 4 . In hydrous calcite slits, calculating the adsorption capacity and density profile of CO 2 and CH 4 , the results show that the gas adsorption sites become progressively occupied by H 2 O molecules, leading to a substantial decrease in the adsorption capacity of CO 2 and CH 4 . Furthermore, by analysis of the adsorption energy and electronic structure, the reason for the reduction of gas adsorption capacity caused by H 2 O is further revealed. This work has a deep understanding of the adsorption mechanisms of shale gas and CO 2 in calcite and can offer valuable theoretical insights for the development of a CO 2 -enhanced shale gas recovery technology.