Pore-scale imaging of hydrogen displacement and trapping in porous media

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 core 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 pore fluid pressure. Hydrogen recovery during secondary imbibition at a capillary number of 2.4 × 10 −6 systematically decreased with pressure, with 80%, 78% and 57% of the initial hydrogen recovered at 2, 5 and 7 MPa, respectively. Injection of brine at increasing capillary numbers up to 9.4 × 10 −6 increased hydrogen recovery. Based on these results, we recommend more shallow, lower pressure sites for future hydrogen storage operations in porous media.