Microscale displacement dynamics of hydrogen and methane in fractured rock: Insights for repurposing natural gas sites for hydrogen storage

Sojwal Manoorkar , Gulce Kalyoncu Pakkaner, Hamdi Omar, Soetkin Barbaix, Dominique Ceursters, Maxime Latinis, Stefanie Van Offenwert, Tom Bultreys 

Converting natural gas sites for hydrogen storage leverages existing infrastructure but requires understanding differences in hydrogen and methane injection/withdrawal dynamics within fractured geological formations. This study examines two-phase flow for hydrogen, methane, and their mixtures in fractured limestone from Belgium's Loenhout site. Experiments at 10 MPa and 65°C show that while drainage produces similar average gas saturations across gases, invasion patterns critically depend on gas properties and fracture geometry. Rougher fractures promote more frequent snap-off events leading to a larger number of smaller hydrogen ganglia compared to methane. Wider fractures yield higher initial gas saturation but lower recovery due to enhanced trapping. During imbibition, gas type exerts a stronger effect: hydrogen achieves near-total recovery in smooth fractures, whereas methane and mixtures leave trapped clusters. In rough fractures, both gases are retained, but hydrogen forms more interconnected ganglia. These results highlight pore-scale mechanisms influencing hydrogen recovery efficiency in fractured storage sites.