Potential technical hazards associated with four North American carbon capture and sequestration projects

Carbon capture and storage (CCS) risks depend upon the site geology, potential CO2-caprock reactions, anthropogenic pathways (legacy wellbores), and well construction and operation. Herein, we assess the major risks, termed 'georisks', acknowledging that quantitative description must be site-specific, although pathway impact generalisations are possible. We discuss geological and pathway issues to guide general site selection practices to reduce georisks. Events that trigger hazards and the consequences are presented for leakage, low storage capacity/injectivity, the release of hazardous gases and materials, surface uplift, and Induced seismicity. A supplementary literature-sourced hazard tabulation was developed with focus on four large-scale North American CCS projects (Quest Project, Weyburn Project, Project Pioneer and FutureGen). Each hazard is classified based on the project phase and trigger activity. The risks of CO2, brine, or other fluid leakage through wells (injection, monitoring, decommissioned legacy wells) remain uncertain, but legacy well gas leakage is common, rather than exceptional, despite modern cementing and completion practices.