Hector George Barnett , Mark T Ireland, Cees van der Land

Future energy systems with greater contributions from renewable energy will require long-duration energy storage to optimise integration of renewable sources, hydrogen is an energy vector that could be utilised for this. Grid-scale underground natural gas storage is already in operation in solution-mined salt caverns, where individual cavern capacities are ~25 - 275 GWh. While traditionally salt caverns have been restricted to being developed onshore, in some offshore locations, such as the UK Continental Shelf, there are extensive evaporites that have potential for storage development. Capacity estimates for offshore areas, typically rely upon generalised regional geological interpretations, frequently do not incorporate site-specific structural and lithological heterogeneities, use static cavern geometries, and use methodologies that are deterministic and not repeatable.
We developed a stochastic method for identifying viable salt cavern locations and estimating conceptual clusters' storage capacity. The workflow incorporates principle geomechanical constraints on cavern development, captures limitations from internal evaporite heterogeneities, and uses the ideal gas law to calculate the volumetric capacity. The workflow accommodates either fixed cavern geometries or geometries that vary per site depending on the thickness of salt. By using a stochastic method, we quantify uncertainties for storage capacity estimates and cavern placement across defined regions of interest. The workflow is easily adaptable allowing users to consider multiple geological models or evaluate the impact of interpretations of varying resolutions.
We illustrate the workflow for four areas and geological models in the UK’s Southern North Sea:
1) Basin Scale (58,900 km2) - >61.9 PWh’s of hydrogen storage with >199,000 cavern locations.
2) Sub-Regional Scale (24,800 km2) – >12.1 PWh’s of hydrogen storage with >36,000 cavern locations.
3) Block Specific – Salt Wall (79.8km2) - >731 TWh’s of hydrogen storage with >400 cavern locations.
4) Block Specific – Layered Evaporite (225 km2) - >419 TWh’s of hydrogen storage with >460 cavern locations.
Our workflow enables reproducible and replicable assessments of site screening and storage capacity estimates. A workflow built around these ideals allows for fully transparent results. We compare our results against other similar studies in literature and find that often highly cited papers have inappropriate methodologies and hence capacities.