Experimental evaluation of rock mineralogy on hydrogen-wettability: Implications for hydrogen geo-storage

Global energy demand is increasing every year, and we face the drawbacks of extensive fossil fuel use in our daily lives more than ever. Hydrogen (H2) is currently assessed as an alternative energy source useful for industries due to its zero post-combustion emission. However, H2 is extremely compressible and volatile, making it difficult to transport and store at the surface. The underground storage of carbon dioxide has been practiced for many years in the oil and gas industry. Thus, implementing a similar approach for H2 seems promising. There is a serious lack of wettability and interfacial tension (IFT) data on H2 exposed to subsurface formations and fluids. Such data are essential for studying the H2 storage/withdrawal capacity in subsurface reservoirs. The role of mineralogy on the wettability of rock is well established; therefore, the influence of the rock type (e.g., calcite, dolomite, quartz, shale, anhydrite, gypsum, granite, and basalt) on the wettability (i.e., the contact angle) of a rock/H2/brine system was evaluated in this work based on realistic (aged with stearic acid) subsurface conditions (pressure: 10–100 bar and temperature: 20 °C–80 °C). In addition, the IFT in the H2/aqueous phase (distilled water and formation brine) was determined. With H2, the organically aged surfaces of calcite, dolomite, shale, and anhydrite become neutral-wet or slightly nonwater-wet. However, the wettability of quartz, granite, gypsum, and basalt samples remain slightly or strongly water-wet with increased pressure and temperature, suggesting higher capacities for H2 geo-storage purposes. The results also indicate that the H2/liquid IFT in DI water and brine increase with increased temperature and salinity, whereas the H2/liquid IFT drops sharply with increased pressure. Thus, the H2/liquid IFT and H2-wettability data for various minerals provide a comprehensive view and reveal the importance of mineral composition. The reservoir schemes and models should gauge the data in this work to correctly estimate geo-storage capacity based on rock mineralogy. The data can improve the feasibility of industrial-scale H2 geo-storage projects and reduce uncertainty and improve containment security.