Wettability of Caprock-H₂-Water: Insights from Molecular Dynamic Simulations and Sessile-Drop Experiment

Structural trapping is the most critical geostorage mechanism utilized in H₂ subsurface storage projects due to the substantial gravity segregation of H₂ and reservoir fluids. Hence, it is crucial to comprehend the wettability of caprocks under H₂ gas storage conditions. Several studies have investigated the wettability of H₂ using the sessile water-drop method on caprocks at various pressures and temperatures; nevertheless, the reported data display significant variability. In this study, molecular dynamic simulation has been coupled with a sessile-drop experiment to estimate the water-H₂-mica, water-H₂-anhydrite, water-H₂-gypsum, and water-H₂-halite wettability under various conditions of pressure, temperature, and salinities. We observed that the clean mica, anhydrite, gypsum, and halite minerals are strongly water-wet under all tested conditions. The analysis of molecular interactions has revealed that the caprock surfaces have high hydration energies, which makes it difficult for H₂ to displace water and alter the wettability of the rock. Consequently, this research suggests that caprocks are strongly water-wet, H₂ does not show wetting phase characteristics, and the considered caprocks have a high sealing efficiency.