Assessing the Feasibility of Carbon Dioxide Sequestration in Abandoned Oil and Gas Wells: A Case Study of the UK Continental Shelf

Abstract This study examines the feasibility of repurposing abandoned offshore wells for geological CO2 storage, focusing on three candidate fields in the UK Continental Shelf (UKCS). The fields were evaluated based on storage capacity, leakage risk, development cost, and distance to shore. A structured ranking approach was used to compare site suitability under multiple weighting scenarios. Field B consistently ranked highest, offering a favourable balance of subsurface integrity, reservoir performance, and accessibility. Existing wells in Field B were screened using the REX-CO2 tool, applying parameters from prior risk-based studies. The resulting moderate risk scores indicate that the wells could be reused following further inspection and minor remediation. Reservoir simulations were performed to model CO2 behaviour over a 200-year period. Under structural trapping, CO2 migrated vertically and accumulated below the caprock, but pressure build-up over time raised containment concerns. In contrast, residual trapping led to greater long-term stability, with more than three-quarter of the injected CO2 staying immobilised after two centuries. The findings demonstrate that Field B meets both geological and operational requirements for CO2 storage. This work provides a practical framework for screening and evaluating mature offshore assets for integration into carbon storage strategies, with broader relevance to similar settings across the North Sea.