Hydrogen wettability of Saudi Arabian Basalt: Implications for H₂ geo-storage

The large-scale subsurface storage of hydrogen is a crucial element of the hydrogen economy value chain and is an essential process for achieving the successful replacement of carbon-based fuels. The wettability of the rock-H₂-brine system, as quantified by contact angle measurement, has been the focus of most recent research due to its impacts on fluid flow, H₂ migration and recovery efficiency during underground hydrogen storage (UHS). However, the reported contact angle data sets are quite inconsistent, and there are relatively few literature reports regarding the contact angles of H₂/brine on Saudi Arabian basalt (SAB) compared to the contact angle data for quartz, shale, mica, and calcite. Hence, the advancing and receding contact angles θ_aandθ_r of the SAB-H₂-brine system are measured herein via the sessile drop method at various temperatures (308 and 323 K) and pressures (0.1–20 MPa) to ascertain the appropriateness of SAB for UHS. The results indicate that the H₂ wettability of SAB generally increases with pressure and temperature, but the pure SAB remains strongly water wet, having θ_a and θ_r<45° under all experimental conditions. Conversely, stearic acid contamination (10⁻² mol/L) is found to be inimical to UHS, with the θ_a increasing from 42.1° for pure SAB to 100.8° for stearic acid aged SAB, while θ_r increases from 36.3° to 94.2°, at 20 MPa and 323 K. At the same temperature of 323 K, the H₂ column heights are found to decrease with pressure, reaching 4663 m and −424 m for the pure SAB and organic acid aged SAB, respectively, at 20 MPa, thereby confirming that organic contamination and increased storage depth are unfavorable for UHS in SAB. These results provide insights into the conditions for achieving favorable UHS in SAB formations.