H2-quartz and cushion gas-quartz intermolecular interactions: implications for hydrogen geo-storage in sandstone reservoirs

Abstract

Emissions of carbon dioxide (CO 2 ) from fossil fuel usage continue to be an incredibly challenging problem to the attainment of CO 2 free global economy; carbon Capture and Storage (CCS) and the substitution of fossil fuel with clean hydrogen have been identi ed as signi cant primary techniques of achieving net zero carbon emissions. However, predicting the number of gas trapped in the geological storage media effectively and safely is essential in attaining decarbonisation objectives and the hydrogen economy. Successful underground storage of carbon dioxide and hydrogen depends on the wettability of the storage/cap rocks as well as the interfacial interaction between subsurface rocks, the injected gas, and the formation of brine. A key challenge in determining these factors through experimental studies is the presence of con icting contact angle data and the di culty of accurately replicating subsurface conditions in the laboratory. To address this issue, molecular dynamics simulations offer a microscopic approach to recreating subsurface conditions and resolving experimentally inconsistent results. Herein, we report the molecular dynamics simulation results for hydrogen (H 2 ) and cushion gas ( e.g., CO 2 and N 2 ) on quartz surfaces to understand the capillary and trapping of these gases in sandstone formations. The results of these three gasses were compared to one another. The simulation predictions showed that the intermolecular interactions at the CO 2 -quartz surface area are more substantial than at the N 2 and H 2 -quartz interface, suggesting that the quartz surface is more CO 2 -wet than N 2 and H 2 -wet under the same circumstances. In addition, it was found that CO 2 has a substantially higher adsorption rate (~ 65 Kcal/mol) than N 2 (~ 5 Kcal/mol) and H 2 (~ 0.5 Kcal/mol). This phenomenon can be explained by the fact that CO 2 density is substantially larger than N 2 /H 2 density at the same geo-storage conditions. As a result, CO 2 could be the most favorable cushion gas during underground hydrogen storage (UHS) because a higher CO 2 residual is expected compared to H 2 . However, due to the Van der Waal Interaction force with quartz, only a small amount of H 2 can be withdrawn.