Differentiating legacy wellbores in the scottish north sea using multi-criteria decision analysis with a view to minimising containment risk for carbon capture and storage

Carbon Capture and Storage (CCS) is a critical technology for mitigating climate change by securely storing CO₂ emissions underground. Former oil and gas fields are prime candidates for CCS due to their proven storage capacity, existing infrastructure, and favourable geology. However, legacy wells in these fields pose significant containment risks. Assessing these risks typically requires site-specific evaluations, which are time-intensive and impractical at scale, hindering systematic regional assessments, particularly in areas where CCS is expected to expand. We developed a weight sum model (WSM) multi-criteria decision analysis (MCDA) approach to evaluate the containment risks of 12,264 legacy oil and gas wells in the North Sea. The model was informed by expert elicitation involving 54 global subject matter experts, 70 % of whom are industry professionals with over a decade of CCS experience. Wellbores were assigned consideration scores reflecting their containment risks based on geospatial, temporal, and engineering factors, weighted by expert consensus. The mean consideration score was 0.55 (range: 0–1), with outlier thresholds at 0.74 and 0.36, identifying 506 wells with significantly higher or lower risks to containment. Among Scotland's nine most promising CO₂ storage sites, the Miller Oil Field and Captain Sandstone Fairway represent the highest and lowest cases of consideration score, respectively. By integrating expert knowledge into an MCDA framework, this approach provides a systematic method to prioritise wellbores for further evaluation based on risk profiles, supplementing traditional case-by-case assessments. It offers a scalable solution for managing containment risks across domains with multiple planned CCS projects.