Underground Storage of Hydrogen and Hydrogen/methane Mixtures in Porous Reservoirs: Influence of Reservoir Factors and Engineering Choices on Deliverability and Storage Operations

Seasonal storage of natural gas (NG), which primarily consists of methane (CH4), has been practiced for more than a hundred years at underground gas storage (UGS) facilities that use depleted hydrocarbon reservoirs, saline aquifers, and salt caverns. To support a transition to a hydrogen (H2) economy, similar facilities are envisioned for long-duration, underground H2 storage (UHS) of either H2 or H2/CH4 mixtures. Experience with UGS can be used to guide the deployment of UHS, so we identify and quantify factors (formation/fluid properties and engineering choices) that influence reservoir behavior (e.g., viscous fingering and gravity override), the required number of injection/withdrawal wells, and required storage volume, contrasting the differences between the storage of CH4, H2, and H2/CH4 mixtures. The most important engineering choices are found to be the H2 fraction in H2/CH4 mixtures, storage depth, and injection rate. Storage at greater depths (higher pressure), but with relatively lower temperature, is more favorable because it maximizes volumetric energy-storage density, while minimizing viscous fingering and gravity override due to buoyancy. To store an equivalent amount of energy, storing H2/CH4 mixtures in UHS facilities will require more wells and greater reservoir volume than corresponding UGS facilities. We use our findings to make recommendations about further research needed to guide deployment of UHS in porous reservoirs.