The Microbial Factor in Subsurface Hydrogen Behavior: Implications for Wettability and Interfacial Dynamics

Microbial activity plays a significant role in subsurface hydrogen behavior, with implications for underground storage and natural hydrogen systems. This study examines how microbial processes influence the wettability and solid-liquid interfacial characteristics of key subsurface minerals, calcite, dolomite, quartz, and gypsum, in hydrogen-brine-rock systems under realistic subsurface conditions. Wettability directly affects hydrogen distribution, flow dynamics, and trapping, making it a critical factor for both storage and natural recovery applications. Experiments were conducted under high-pressure, high-temperature conditions, with SEM/EDS analysis used to characterize interfacial modifications and mineral surface changes across three scenarios: clean, organic acid-aged, and microbial-aged. Microbial aging consistently increased mineral hydrophilicity, reducing advancing contact angles, such as from 57° (clean) to 40° (microbial-aged) on calcite at 50 °C and 8 MPa. Similar trends were observed for dolomite, with smaller changes for quartz and gypsum. Microbial biofilms were most prominent on calcite and dolomite surfaces, accompanied by decreases in brine pH (e.g., from 7.4 to 5.2 for calcite). These results reveal how microbial processes reshape mineral properties and hydrogen behavior in the subsurface. This study provides critical insights into microbial-mineral interactions, offering valuable guidance for optimizing hydrogen storage and natural hydrogen recovery systems.