Experimental evaluation of 3-phase and 4-phase surface phenomena for hydrogen storage in depleted oil reservoirs

Surface phenomena play a major role in subsurface gas storage, influencing wettability, fluid displacement, and gas containment efficiency. While extensive studies have examined these interactions in two-phase systems (hydrogen and brine), assuming ideal conditions, the influence of residual crude oil creates a complex three-phase brine–oil–gas interface and a four-phase brine–oil–rock–gas system that have been scarcely explored. We conducted captive-bubble and pendant-drop experiments using a drop-shape analyzer (DSA 100) to measure contact angles (CA) and interfacial tensions (IFT) for H₂–CH₄ mixtures under pressures of 500–3000 psi, temperatures of 30 °C and 70 °C, and brine salinities of 5 wt% and 20 wt% NaCl. The results indicated that all gas mixtures demonstrated strong water-wet conditions, having CAs ranging from 36° to 55°, and revealed that pressure had no significant impact on either CA or IFT. Conversely, salinity and temperature effects were more pronounced. In the case of IFT, both temperature and salinity exhibited a decreasing trend for the brine/oil/H₂–CH₄ system. Based on the conditions investigated, a gas mixture containing 80–50 % H₂ and 20–50 % CH₄ was identified as the optimal composition, offering the best performance in terms of storage and withdrawal. The present work offers significant contributions to the understanding of interfacial processes in three-phase systems therefore enhancing the approach to optimize hydrogen storage methods in depleted oil reservoirs.