Abstract

Hydrogen (H₂) has been an attractive energy carrier and its appeal is not in just powering cars but its true potential is in decarbonizing industries such as heating of buildings and transportation 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, which have 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 and reliable 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: caverns, salt domes, aquifers, and depleted oil/gas fields where large quantities of gaseous hydrogen can be safely and cost effectively stored. Underground geologic storage must have adequate capacity, ability to inject/extract high volumes, and 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 (i.e., green hydrogen coupled with wind farms).

We have carefully evaluated existing non-isothermal compositional gas reservoir simulator(s) and their suitability for hydrogen storage and withdrawal from aquifers or depleted oil/gas reservoirs. We have successfully calibrated the gas equation of state model against published laboratory measurements of H₂ density and viscosity as a function of pressure and temperature. Our numerical simulations of H₂ in aquifer and oil reservoirs indicated the critical need to contain the stored volume (working gas) due to H₂ high mobility (low density and viscosity). The latter objective can be achieved with an integrated approach of site selection and its geological features (i.e., faults/natural fractures, caprock properties), well locations, and the need for pump wells to maximize the gas capacity and displacing the in-situ fluids.