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

Abstract

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&RTM), 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.

An Experimental Study on Effects of Static CO2 on Cement under High-Pressure/High-Temperature Conditions

“…The interaction between cement and CO 2 in the rocks has gained significance in recent years Moroni et al 2009;Brandl et al 2010;Le Guen et al 2008). Geological storage of CO 2 in depleted and partially depleted oil fields has gained increasing global interest as an economically viable means of reducing CO 2 emissions, while recovering extra oil.…”

Risk Assessment-Led Characterisation of the SiteChar UK North Sea Site for the Geological Storage of CO2

“…3.4.16) and the mass of CO 2 leakage to the secondary reservoir was also reduced. Risk mitigation measures of additional well characterisation (Le Guen et al, 2008) are suggested and included as part of the preventative measures plan (Hannis et al, 2013c;Shi et al, 2013) and 'dry-run' storage permit application for the site (Hannis et al, 2013a). Baseline observation and resurvey of the sea bed during injection over existing well sites by sonar and echo sounder surveys (Shi et al, 2013) are a component of the monitoring plan (Hannis et al, 2013c).…”

Long-Term Study of Effects of CO2 Exposure on Cement Integrity Under Downhole Conditions

“…The interaction between cement and CO 2 in the formation has been an area of interest in recent years Moroni et al 2009;Brandl et al 2010;Le Guen et al 2008). When cement hydrates, the major products formed during the hydration reaction are calcium hydroxide (portlandite), calciumsilicate-hydrate (C-S-H), ettringite, and monosulfate.…”