Hydrogen (H2) is an attractive energy carrier, and its true potential is in decarbonizing industry through 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 provided primarily by using natural gas and transportation by gasoline with a large carbon footprint. Hydrogen has a similarly high energy density, but technical challenges are preventing its large-scale use as an energy carrier. Among these is 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. Several options exist 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depleted oil/gas reservoirs where large quantities of gaseous hydrogen can be safely and cost-effectively stored and withdrawn as needed.
The requirements of suitable subsurface geological storage sites for hydrogen are sufficient storage capacity, containment with minimal losses, cost-effectiveness, and a delivery rate that reliably meets power demand. Aquifers have an abundant storage capacity, require simpler modeling and fluid characterization, and can maintain the purity of hydrogen when produced back. Aquifers have some drawbacks, however, such as the lack of a proven trapping structures, the risk of leakage with new wells, and the added cost of fully characterizing the formation and building infrastructures such as pipelines and production facilities. On the other hand, depleted hydrocarbon reservoirs have a proven record of adequately trapping oil and gas and would require less capital investment given the existing reservoir characterization and infrastructure. Their drawbacks manifest in the complexity of three-phase flow requiring extensive fluid characterization and complex numerical modeling. Additionally, storing hydrogen in these reservoirs will cause mixing between hydrogen and the in-situ hydrocarbons, which will decrease the purity of the produced hydrogen.
In this paper, a commercial reservoir simulator was used to model cyclic injection/withdrawal from saline aquifers and depleted oil/gas reservoirs. The phase behavior, fluid properties, and petrophysical models were calibrated against published laboratory data of density, viscosity, and relative permeability. The history-matched dynamic models of two CO2 injection field projects in saline aquifers and one natural gas storage in a depleted oil reservoir were considered as hypothetical hydrogen seasonal storage. The results revealed the need to contain the stored volume with an integrated approach to site selection, well locations, and operation to maximize the capacity and deliverability.
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