Stability evaluation of CO₂ hydrate barrier layers in porous media with different surface areas and wettabilities by water permeability measurements

CO₂ hydrate formation within the gas hydrate stability zone is expected to provide a redundant safety barrier for sub-seabed geological CO₂ storage by suppressing fluid flow during leakage. However, hydrate morphology and sealing performance in porous media depend strongly on rock properties, including particle size and wettability. In this study, seabed sediments were simulated using packed glass beads (0.05–0.21 mm) with hydrophilic and hydrophobic surfaces. After hydrate formation, water was injected and barrier performance was quantified using permeability reduction and the relative pressure rise rate during injection. Hydrate formation reduced permeability by up to four orders of magnitude compared with the no-hydrate case. For intermediate particle sizes (0.07–0.15 mm), hydrophilic conditions promoted more stable hydrate barriers, whereas hydrophobic conditions tended to cause intermittent re-opening and re-formation. The finest particles (0.05 mm) exhibited strong flow inhibition regardless of wettability, consistent with a larger specific surface area available for hydrate growth. These results provide quantitative constraints for predicting hydrate barrier development and strengthening risk assessment for sub-seabed CO₂ storage.