Carbon Capture and Storage (CCS) is a technology that can help to reduce greenhouse gas emissions. However, there are risks associated with CCS; for the storage element, this includes the risk that the storage site is not technically suitable for long-term storage of large volumes of CO2. Key risk factors include insufficient capacity for the anticipated injectate volume, poor injectivity quality, and loss of containment risk including the potential for measurable CO2 leaks.
It is important for storage project developers to understand that CO2 storage is not the same as hydrocarbon production in reverse. CO2 is a different fluid, both chemically and thermodynamically, with variable properties under surface and subsurface conditions, and particularly as pressurization occurs over time.
There are both international and country-specific regulatory frameworks and requirements in place for CO2 storage which are separate to those directed at Enhanced Hydrocarbon Recovery (EHR) or waterflooding. These regulations are based on site-specific risk elements of a project and focus on how risk assessments must be conducted and managed, ensuring that other natural resources, human health, and the environment are not harmed.
A Containment Risk Assessment (CRA) is an important part of the CO2 storage site selection process. The CRA identifies potential leak-paths and evaluates the likelihood and severity of any leakage. The CRA also helps to focus the design of a Measure, Monitoring and Verification (MMV) plan.
The MMV plan includes both a technology selection and implementation plan, and a response plan including proportionate corrective measures in case of (suspected) leakage. A holistic CRA includes a multi-disciplinary analysis of the geological storage complex, incorporating legacy wells and future injector and monitor wells. The behavior of injected CO2 is simulated, resulting in the expected maximum extent of the CO2 plume and possible displaced fluids. All potential leak-paths, regardless of their perceived likelihood, are evaluated. Barriers physically preventing CO2 from leaving the storage complex, as well as mitigating measures that can either prevent and/or minimize the severity of any leakage, are mapped, and compiled into bowtie diagrams.
