The critical evaluation of carbon dioxide subsurface storage sites: Geological challenges in the depleted fields of Liverpool Bay

Depleted hydrocarbon fields in the Liverpool Bay area of the United Kingdom East Irish Sea have been earmarked as sites for the geological storage of CO₂. Cessation of production at the Hamilton field means that it will soon be available for storage and has led to its inclusion in the United Kingdom’s first (track 1) carbon capture, utilization, and storage cluster sequencing that underpins efforts to decarbonize onshore emitters (HyNet project). The interpretation of well-calibrated, proprietary three-dimensional seismic data has enabled critical assessment of the geological controls on CO₂ storage in the area. Our mapping demonstrates that significant portions of the fields lie shallower than the 800-m depth threshold, above which lower pressures and temperatures prevent CO₂ from being stored in the most efficient supercritical phase, significantly reducing storage capacity during the early phases of injection. Furthermore, an assessment of the Mercia Mudstone Group seal highlights the presence of a gas-bearing basal Ansdell Mudstone Member to the Ormskirk Sandstone Formation reservoirs forming a waste zone that extends the reservoir section to even shallower levels. The mapping of faults to near seabed and progressive younging and shallowing of the ultimate top seal resulting from a progressive pinch-out of halite horizons in the Mercia Mudstone Group raise additional questions about the integrity of the top seal in southern parts of the basin.