A group of scientists led by the Dublin City University in Ireland has analyzed the prospects of underground hydrogen storage (UHS) in geological formations in a comprehensive review and has found that depleted oil and gas reservoirs are the cheapest options.
In addition to oil and gas reservoirs, the techno-economic analyses considered hydrogen storage in aquifers, porous rocks, and salt caverns. “It should be mentioned that salt caverns do not exist naturally,” it explained. “Instead, they are artificial cavities in underground salt formations, that are created by the controlled dissolution of rock salt through water injection during the solution mining process.”
All these geological formations may ensure a series of advantages in terms of safety such as good gas tightness, high wall sealing thicknesses, and extensive subsurface depths. “It is worth noting that UHS can benefit from the technological maturity of the geologic storage of natural gas and CO2, which are associated with decades of established knowledge,” the researchers noted. “However, H2 is invariably more chemically, biologically, and microbially reactive, which presents unique challenges that are yet to be fully understood.”
Furthermore, compared to conventional natural gas storage, UHS has leakage issues, due to viscosity, the molecule size of hydrogen, and the lower density, which requires more pressure and in turn affects storage capacity.
The analyses showed that the cost of UHS depends on transportation, monitoring, storage, and injection cost, as well as the location and properties of the geological storage site. Capital costs included gas compression, transformer installation, piping, transformer installation, new well drilling, and wellhead equipment installation.
The researchers found that depleted oil and gas reservoirs are the cheapest storage option with a cost of $1.29/kg, while rock caverns offer the highest levelized cost of storage of $2.77/kg. Capital expenditure for gas and oil reservoirs was also the lowest at $0.73/kg and salt caverns had the highest capital expenditure of $1.51/kg. The academics emphasized that the operating expense was also lower ($0.11/kg ) when compared to salt caverns ($0.14/kg ), noting that depleted natural gas reservoirs have a lower construction cost when compared with depleted oil reservoirs.
They introduced their findings in the paper “Perspectives and prospects of underground hydrogen storage and natural hydrogen,” published in Sustainable Energy Fuels. “Despite the scarcity of economic data on natural hydrogen projects, it is expected that the overall economics of its extraction will not be too different from natural gas,” they concluded. “Nonetheless, this requires further substantiation via robust techno-economic analyses.”
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