Conor O'Sullivan, Pablo Rodriguez-Salgado, Conrad Childs, Patrick Shannon

As Ireland looks westwards to its Atlantic coastline to develop its renewable energy ambitions, offshore sedimentary basins on the Irish Atlantic margin offer significant potential for either collaborative energy (e.g. hydrogen, H2) or carbon dioxide (CO2) storage. Methodologies for subsurface storage assessment developed for basins with dense data coverage are typically less applicable to underexplored sedimentary basins. Therefore, a workflow is presented for subsurface storage assessment in underexplored basins which uses existing datasets to identify structural traps and populate a gas-in-place equation. This workflow is then applied to the Irish Atlantic margin; The geology of the Slyne, Erris, and Donegal basins is reviewed to understand their potential for subsurface storage. Jurassic, Triassic and Carboniferous reservoirs are investigated to understand their reservoir quality, extent, and the integrity of related seals. Structural trap types within the study area are then described and the storage assessment workflow is applied to three candidate sites with varying levels of data coverage. Across these three sites, P50 storage volumes equivalent to 720 million tonnes of CO2 or 318 terawatt hours of H2 are estimated. The results highlight the potential for underexplored sedimentary basins on the Irish Atlantic margin to support the deployment of offshore renewable energy projects and reduce Ireland's CO2 emissions. This workflow is applicable to a variety underexplored sedimentary basins with limited data coverage and emphasises the utility of legacy hydrocarbon datasets for early-stage subsurface storage assessment.