Journal of African Development

Hydrogen (H₂) is an essential energy vector for the global shift to cleaner power yet storing it at scale above ground remains both technically and environmentally challenging. Underground hydrogen storage (UHS) offers a viable alternative, but gas mobility and trapping behaviour are strongly controlled by interfacial processes. This study focuses on interfacial tension variations in H₂-CO₂-brine systems, under subsurface conditions, focusing on the effects of pressure (10–100 bar), temperature (20–80 °C), salinity, and gas composition.

Gas-liquid IFT (γLG) was measured experimentally in distilled water and formation brine. Results show that IFT in pure H₂–water systems increase with temperature, whereas in H₂–brine systems it decreases due to salt-driven modifications to intermolecular forces. CO₂-containing mixtures exhibit stronger pressure dependence, with increasing pressure lowering IFT through enhanced CO₂ solubility and molecular interactions. Additionally, CO₂ as a cushion gas played a crucial role in improving hydrogen mobility and storage efficiency by reducing IFT, thereby minimizing capillary trapping and enhancing gas injectivity. The observed nonlinear pressure dependence at higher CO₂ concentrations underscores the complexity of multiphase interactions in subsurface environments, emphasizing the need for accurate modelling in UHS. The findings contribute to the fundamental understanding of gas-fluid interactions under reservoir conditions and support the development of more efficient hydrogen storage and carbon sequestration strategies