Clay-hydrogen and clay-cushion gas interfacial tensions: Implications for hydrogen storage

Rock/fluid interfacial tension (γ_rock−fluid) govern the fluid flow dynamics, the injection/withdrawal rates, the gas storage capacity, and containment integrity during gas (H₂, CO₂, N₂) geo-storage. Clay-gas interfacial tension (γ_clay−gas) data, especially for the clay-H₂ (γ_clay−H2), the clay-N₂ (γ_clay−N2) and the clay-CO₂ (γ_clay−CO2) systems, have rarely been reported in the literature due to the challenging nature of these measurements in the laboratory. In this study, Neumann's equation of state and Young-Laplace equation was combined to compute clay-gas and clay-brine interfacial tensions (IFT) parameters at realistic geo-storage temperature (333 K) and pressure (5–20 MPa). Our results show that at similar thermodynamic conditions: γ_clay−H2 >γ_clay−N2>γ_clay−CO2. Our calculations also showed that: γ_{kaolinite−N2}>γ_illite−N2>γ_{montmorillonite−N2}, and γ_{kaolinite−CO2}>γ_illite−CO2>γ_{montmorillonite−CO2}. In contrast, for hydrogen a negligible difference in γ_clay−H2 was obtained for the three clay types, although, the IFT between clay minerals and brine in presence of hydrogen is different for these three clay types. Overall, computed γ_clay−H2 values were higher than γ_clay−N2 and γ_clay−CO2 values, whereas computed clay-brine interfacial tension was lower in presence of hydrogen compared to carbon dioxide and nitrogen. These results suggest that nitrogen and carbon dioxide could be used as favorable cushion gas for maintaining formation pressure during underground hydrogen storage. We also demonstrated a remarkable relationship between clay/gas IFT and gas density that could serve as a helpful tool for quick estimation of rock-fluid interfacial tension.