Translating risk assessment to contingency planning for CO2 geologic storage: A methodological framework

Abstract

In order to ensure safe and effective long-term geologic storage of carbon dioxide (CO2), existing regulations require both assessing leakage risks and responding to leakage incidents through corrective measures. However, until now, these two pieces of risk management have been usually addressed separately. This study proposes a methodological framework that bridges risk assessment to corrective measures through clear and collaborative contingency planning. We achieve this goal in three consecutive steps. First, a probabilistic risk assessment (PRA) approach is adopted to characterize potential leakage features, events and processes (FEP) in a Bayesian events tree (BET), resulting in a risk assessment matrix (RAM). The RAM depicts a mutually exclusive and collectively exhaustive set of leakage scenarios with quantified likelihood, impact, and tolerance levels. Second, the risk assessment matrix is translated to a contingency planning matrix (CPM) that incorporates a tiered-contingency system for risk-preparedness and incident-response. The leakage likelihood and impact dimensions of RAM are translated to resource proximity and variety dimensions in CPM, respectively. To ensure both rapid and thorough contingency planning, more likely or frequent risks require more proximate resources while more impactful risks require more various resources. In addition, the minimum and maximum risk tolerance levels are translated to contingency thresholds, and all tolerable risk scenarios are categorized under three contingency tiers: Tier 1, Tier 2, and Tier 3. We highlight how the upper, lower, and inter-tier contingency boundaries should be collaboratively pre-negotiated between the operating party and multiple relevant stakeholders to ensure effective preparedness and response. Finally, we present a model contingency plan to demonstrate how all newly introduced concepts integrate together. Specifically, we focus on explaining how the designed contingency tiers facilitate important aspects of contingency planning, primarily: evaluating leakage and initiating response; designing a corrective measures matrix (CMM) that assigns specific control and remediation measures to each leakage scenario; mobilizing, deploying, and sustaining necessary human and equipment resources; and formulating a decision-making hierarchy, a notification protocol, and a communication scheme to effectively administer the CO2 storage site.