A new stratigraphic trap for CO2 in the UK North Sea: appraisal using legacy information

Using legacy information to search for geological CO2 storage within saline aquifers is likely to be a cost-effective technique for commercial CCS projects. Here, a potential storage site was discovered, away from hydrocarbon reservoirs, using public information. CO2 would be injected 15–40 km downdip from the margin of almost un-drilled regionally extensive Permian (Rotliegend) Sandstone saline aquifer. The CO2 would migrate buoyantly towards the aquifer margin under an evaporite top-seal, becoming partly trapped by residual saturation effects. Any remaining CO2 would be retained in the stratigraphic pinch-out trap at the edge of the aquifer. The lateral seal at the margin is most likely to be metamorphic basement – of presumed low permeability, inferred to be overlain by dolomite-anhydrite sediments. Using conservative assumptions, 170–690 Mt of CO2 could be stored along a 50 km long section of the 300 km margin of the reservoir. Preliminary modelling shows that 100% of the CO2 will be retained within the reservoir for at least 10,000 years. This demonstrates how small datasets, widely spread, can be adequate for a first stage investigation, and geological uncertainties can be identified for subsequent investigation.