Hydrogen wettability of limestone, dolomite, and anhydrite in binary mixtures of CH₄ and CO₂

Underground Hydrogen Storage (UHS) has been proposed as a potential solution to the large-scale energy storage required to establish a net zero emissions society. The success of UHS, however, depends on several geological and petrophysical parameters of the host rock, including wettability, which dictates the plume migration pathway in the pore structure and extraction efficiency of the stored hydrogen. In this study, the changes in wettability of carbonates and anhydrite to H₂ in binary mixtures of CH₄ and CO₂ were evaluated using the gas/water/rock contact angle (CA) measurements at various pressures (3.44–17.23 MPa) and temperatures (30 °C and 75 °C). The results obtained showed that these binary mixtures have no significant impact on the H₂ wettability of the selected carbonate samples. Although the CA of CO₂/water systems was slightly higher than that of CH₄/water due to CO₂ density, all measured CA data sets remained below 34° under all assessed conditions, indicating that the carbonate samples maintained their initial highly hydrophilic state despite the presence of gaseous impurities. It was concluded that during UHS, the in-situ CH₄ and CO₂ in depleted gas reservoirs and the mixing of H₂ with them as potential cushion gases will not have a significant impact on the wetting behaviour of the carbonate with changing temperatures and increasing storage depth.