Role of microbially derived acetic acid in condensate reservoirs for hydrogen storage: Insight into 3-phase and 4-phase surface phenomena with acetic acid and nitrogen cushion gas

Microbial processes in subsurface environments significantly influence interfacial properties that govern hydrogen geo-storage performance. Among microbial byproducts, acetic acid - produced through acetogenesis - is particularly impactful due to its ability to alter fluid–fluid and fluid–rock interactions. However, its effects in realistic 3-phase (brine–gas–condensate) and 4-phase (brine–gas–condensate–rock) systems remain poorly documented. To address this gap, this study quantitatively investigates the ex-situ effect of 100 ppm acetic acid, treated as a microbially relevant metabolite, on contact angle (CA) and interfacial tension (IFT) in condensate-bearing H₂–N₂ storage systems using quartz and Wolfcamp shale (WC shale) substrates, while also evaluating optimal working and cushion gas ratios. Experiments were performed at 2 and 5 wt% NaCl, temperatures of 30 and 50 °C, pressures from 1000 to 3000 psi, and H₂:N₂ ratios ranging from 0 to 100%.Results show that increasing salinity and N₂ concentration generally elevate CA, indicating reduced water-wetness, whereas higher temperatures consistently lower CA and promote brine spreading. IFT increased with salinity but decreased with temperature and pressure. Acetic acid addition consistently lowered IFT, whereas its effect on CA was condition-dependent, generally promoting lower CA values and more water-wet behavior at low salinity but showing smaller or occasionally reversed shifts under some higher-salinity and elevated-temperature conditions. Integrating these interfacial trends with gas-column-height analysis indicates that Mixture 2 (60% H₂ + 40% N₂) is the most favorable formulation within the interfacial-capillary criteria evaluated here for low salinity and moderate temperature (30–50 °C), while Mixture 4 (40% H₂ + 60% N₂) and Mixture 2 remain comparatively favorable at higher salinity. These rankings were interpreted as screening-level interfacial results rather than full reservoir-scale operational optima.The novelty of this work lies in providing, to our knowledge, the first ex situ experimental assessment of microbially derived acetic acid in condensate-bearing multiphase hydrogen geo-systems using coupled 3-phase IFT, 4-phase wettability, and capillary-column-height analyses. Future work should extend this framework to include variable acid concentrations, reactive mineralogical characterization, cyclic wettability behavior, and pore-scale to reservoir-scale upscaling.