Eike Marie Thaysen , Ian Butler, Aliakbar Hassanpouryouzband, Damien Freitas, Fernando Alvarez-Borges, Sam Krevor, Niklas Heinemann, Robert Atwood, Katriona Edlmann 

Hydrogen can act as an energy store to balance supply and demand in the renewable energy sector. Hydrogen storage in subsurface porous media could deliver high storage capacities but the volume of recoverable hydrogen is unknown. We imaged the displacement and capillary trapping of hydrogen by brine in a Clashach sandstone cylinder at 2-7 MPa pore fluid pressure using X-ray computed microtomography. Hydrogen saturation obtained during drainage at capillary numbers of <10-7 was ~50% of the pore volume and independent of the injection pressure. Fluid configuration in the pore space was indicative of a water wetting system at all conditions. Capillary trapping of hydrogen via snap-off during secondary imbibition at a capillary number of 2.4x10-6 systematically increased with pressure, 20%, 24% and 43% of the initial hydrogen trapped at 2, 5 and 7 MPa, respectively. Injection of brine at increasing capillary numbers up to 9.4x10-6 reduced capillary trapping. Based on these results, we recommend more shallow, lower pressure sites for future hydrogen storage operations in porous media.