Long-term risk assessment of subsurface carbon storage: analogues, workflows and quantification

Abstract

A key aspect of transferrable oil and gas expertise to subsurface CO2 storage (SCS) relates to risk assessment. While initial subsurface risk and volume assessments for SCS projects are similar to oil and gas prospect evaluations, full life-cycle risk assessment requires evaluation of the current knowledge of the storage complex and future potential events that may have impacts over long time frames. It is important to learn from past water, gas, and CO2 injection and storage projects, examples of which are reviewed here. The concepts of aleatory and epistemic risk and uncertainty are discussed, and the use of standard risk matrices for evaluation of long-term, low-frequency but potentially high-impact events is challenged. Drawing on the large volume of previous work, this paper highlights key elements for development of a robust risking framework, including thorough project framing and implementation of a staged approach to project execution. The paper assesses methods for ensuring all potential hazards are captured and addresses the challenges of defining a quantitative risking scale suitable for long-term SCS projects. Example quantitative risk profiles can be used to calculate the timing and duration of ‘Peak Risk’, augment monitoring and mitigation planning for management of risk and capital exposure, and help to ensure successful project outcomes.