CO₂ Storage—Managing the Risk Associated With Well Leakage over Long Timescales

One of the major challenges associated with CO₂ geological storage is the performance of the confining system over long timescales. In particular, the occurrence of CO₂ leakage through existing wells could not only defeat the purpose of storage but also badly affect human health or the environment. Indeed, cement degradation and casing corrosion in injection, production or abandoned wells can create preferential channels over time, allowing migration of CO₂ from the reservoir to shallower formations (e.g. aquifers), and/or to the surface.

In this paper, a risk-based approach is proposed for well integrity and confinement performance management. The approach, based on Performance and Risk Management methodology (P&R™), serves as a decision support tool. The major steps are (i) identifying the system and the sources of degradation through characterization and system analysis; (ii) quantifying their criticity through modeling, in terms of probability and severity, and (iii) establishing a risk mitigation plan. This methodology is based on experience in material aging and risk assessment of complex systems, like nuclear structures, where probabilistic simulations are performed. It accounts for all stakes involved in well integrity management and enables the full integration of uncertainties as part of risk estimation.

The methodology presented here greatly improves common approaches based on "Features, Events, and Processes" as it quantifies risk levels. It provides useful and reliable tools to support decisions for well integrity management strategies or emergency plans. To that purpose, mitigation actions such as characterization/inspection, remediation (workover), design improvement or monitoring are valued based on a cost/benefits ratio. Moreover, updating risk assessment with incoming data allows for an evolving vision of risk levels to optimize interventions in time.

This approach is successfully applied, leading to recommendations for safer and more efficient design, maintenance, and monitoring strategies.