Carbon Storage
Containment Risk Assessment
Subsurface CO2 storage is subjected to a Containment Risk Assessment (CRA), which forms part of any permit application. It is important that a CRA presents information to allow stakeholders to make informed judgements about the nature and acceptability of risks posed by subsurface storage. As different stakeholders will have different requirements, a range of approaches may be required. The choice of strategy should take into account the quality of information available and the complexity of the situation. Nevertheless, established risk assessment techniques can be successfully adapted and applied to geological CO2 storage.
Through collaborative development of a subsurface storage CRA, Risktec supports CCUS projects through permissions, licences, approvals, consents and stakeholder engagement. Furthermore, there is a symbiotic relationship between the CRA and the strategies and plans developed by the project (e.g. storage design, injection strategy, monitoring strategy and corrective measures plan):
- The CRA makes claims on the strategies (and the activities which evolve from them).
- The risk-based strategies rely on the CRA to identify the most significant contributors to the overall risk (which must be addressed by the strategies), thereby preventing resources being wasted on scenarios which contribute negligible risk.
Services we provide
Hazard Identification: A carbon storage HAZID will consider man-made and naturally occurring risks i.e. events that can trigger release of CO2 from storage or routes out of the storage formation. Additionally, due to the size and longevity of the storage complex, there is also an emphasis on interactions with third parties.
Bowtie Analysis: Bowtie diagrams can illustrate CO2 leak paths from storage and the natural, engineered and operational barriers. Natural barriers are inherently heterogenic and anisotropic, so subsurface storage bowtie analysis necessarily considers barrier uncertainty and criticality, to allow further work to focus on the least certain and most critical areas.
Quantitative Risk Assessment: Event trees can be used for critical legacy wells to determine the likelihood of CO2 leak rates via abandoned wellbores. A Layers of Protection Analysis (LOPA) style assessment can give an indication of the most likely and most severe geological leak paths. Again uncertainty in barrier ‘failure rate’ can be taken into account. Quantitative estimation of leakage rates for individual wells and quantitative risk analysis of CO2 storage sites and complexes can also be conducted.
Risk Reduction: ALARP assessment is generally qualitative, and workshop-based using bowtie diagrams as a starting point. Typically risks are reduced by decreasing uncertainty, which is achieved by collecting additional or better data, and by conducting further modelling or analysis.