Molecular simulation of H₂, CO₂ and CH₄ adsorption on kerogen in moisture-rich environments

Understanding gas adsorption in organic-rich shales is critical for evaluating their role in CO₂ sequestration and underground hydrogen storage. In this study, grand canonical Monte Carlo (GCMC) simulations were performed to investigate the adsorption behavior of carbon dioxide (CO₂), methane (CH₄), and hydrogen (H₂) on Type II kerogen at two maturity levels (immature II-A and post-mature II-D) under both dry and moisture-rich conditions. Results show that CO₂ consistently exhibits the strongest adsorption due to its quadrupole moment and interaction with heteroatom functional groups, followed by CH₄, while H₂ shows the weakest affinity governed by van der Waals forces. Kerogen maturity significantly enhances adsorption, with II-D outperforming II-A due to greater aromaticity and micropore volume. However, pre-adsorbed water sharply reduces adsorption of all gases by occupying polar sites and clustering within pores. Moisture reduces CO₂ capacity by >98%, nearly eliminates CH₄ uptake, and suppresses H₂ to trace levels. Despite these reductions, moisture increases CO₂/CH₄ and CO₂/H₂ selectivity, as CO₂ retains minimal residual adsorption while CH₄ and H₂ is almost completely excluded. These findings highlight the role of kerogen maturity and moisture in controlling gas storage, with key implications for optimizing CO₂ sequestration and assessing the feasibility of shale formations for H₂ storage.