Aquifer storage

Aquifers are similar to natural gas reservoirs in that they are porous sedimentary rock structures, but contain water instead of natural gas. The main requirements for storage are the presence of a reservoir with a dome shape or structural fault to allow the gas to be trapped at the top of the structure, and the presence of a seal over the reservoir consisting of an impermeable formation. All of the challenges identified for depleted gas fields are relevant to aquifers, but aquifers present additional challenges. Unlike depleted gas fields, which are known to be tight because they were originally filled with gas, aquifers may not be tight on all sides and extensive geological investigation is required to determine whether there are pathways for the gas to escape. With the exception of existing aquifer storage and geothermal production sites, aquifers are undeveloped, with no production wells or surface facilities. As aquifers are water-bearing, moving water can cause significant hydrogen trapping during hydrogen injection, resulting in hydrogen loss. Compared to salt caverns and depleted gas reservoirs, aquifers have the advantage of being more widely available.