An integrated Risk–Integrity–Monitoring (RIM) framework for CO₂ storage in depleted oil and gas reservoirs

The safe and sustainable deployment of carbon capture and storage (CCS) requires long-term reservoir integrity and effective monitoring of environmental risks during operation and post-closure. Depleted oil and gas reservoirs are attractive candidates for large-scale CO₂ storage because of their proven trapping performance, existing infrastructure, and extensive subsurface characterization. However, these reservoirs also present distinct challenges, including legacy well leakage, geomechanical reactivation, and complex fluid–rock–brine interactions. This review presents an Integrated Risk–Integrity–Monitoring (RIM) framework that links environmental risk assessment, containment integrity evaluation, and monitoring strategies into a unified decision-support system for CO₂ storage in depleted reservoirs. The framework synthesizes key degradation mechanisms affecting wells and caprocks, pressure and saturation dynamics, and the capabilities of advanced monitoring technologies, including fiber-optic sensing, time-lapse seismic imaging, and artificial intelligence (AI)-assisted anomaly detection. Illustrative case studies from the Weyburn–Midale, In Salah, and Otway projects demonstrate how adaptive monitoring and operational feedback can reduce long-term containment risk. The RIM framework provides a structured foundation for performance-based regulation and predictive risk management by explicitly linking subsurface integrity indicators to monitoring feedback and governance decisions. By integrating engineering, digital, and policy dimensions, depleted reservoirs can be deployed as safe, verifiable, and scalable components of global net-zero strategies.