Pros and Cons of Saline Aquifers Against Depleted Hydrocarbon Reservoirs for Hydrogen Energy Storage

Hydrogen (H2) is an attractive energy carrier and its true potential is in decarbonizing industries such as providing heat for buildings and being a reliable fuel for trains, buses, and heavy trucks. Industry is already making tremendous progress in cutting costs and improving efficiency of hydrogen infrastructure. Currently heating is primarily provided by using natural gas and transportation by gasoline with a large carbon footprint. Hydrogen has a similarly high energy density but there are technical challenges preventing its large-scale use as an energy carrier. Among these include the difficulty of developing large storage capacities. Underground geologic storage of hydrogen could offer substantial storage capacity at low cost as well as buffer capacity to meet changing seasonal demands or possible disruptions in supply. There are several options for large-scale hydrogen underground storage: lined caverns, salt domes, saline aquifers, and depleted oil/gas reservoirs where large quantities of gaseous hydrogen can be safely and cost-effectively stored and withdrawn as needed. Underground geologic storage must have adequate capacity, ability to inject/extract high volumes with a reliable caprock. A thorough study is essential for a large number of site surveys to locate and fully characterize the subsurface geological storage sites both onshore and offshore. A non-isothermal compositional gas reservoir simulator and its suitability for hydrogen storage and withdrawal from saline aquifers and depleted oil/gas reservoirs was evaluated. The phase behavior, fluid properties, and petrophysical models were all calibrated against published laboratory data of density, viscosity, relative permeability, and capillary pressure for a given site. History-matched dynamic models of two CO2 injection field projects in saline aquifers and one natural gas storage in depleted oil reservoir were considered as hypothetical hydrogen seasonal storage sites. The results revealed the need to contain the stored working gas volume because of high mobility of gaseous H2 with an integrated approach of site selection and its geological features, well locations, and the need for pump wells to maximize the capacity and deliverability.