Features, Events and Processes

System analysis methods have been widely applied in the field of safety and performance assessment for radioactive waste disposal and geological storage of carbon dioxide. As part of the analysis, the system of interest needs to be described in terms of relevant Features, Events and Processes (FEPs). FEPs can provide the basis for developing a comprehensive understanding of the system and evaluating its performance and safety.

As part of the RISCS project, Quintessa developed a generic FEP database for the geological storage of carbon dioxide, with the chosen FEPs being included for their relevance to the long-term safety and performance of the storage system after injection of carbon dioxide has been completed and the injection boreholes have been sealed. Some FEPs associated with the injection phase are nevertheless considered where these can affect long-term performance. The database currently includes around 200 FEPs in a hierarchical structure, with individual FEPs grouped into eight categories. Each FEP has a text description and an associated discussion of its relevance to long-term performance and safety. Quintessa used the FEP database in supporting the NSTA (formerly, the OGA) to identify and describe the risks and mitigations which must be considered as part of carbon storage projects on the UKCS, including well integrity risks.

Quintessa has been also been developing a generic FEP database for decommissioning of wells / boreholes, which includes around 240 FEPs. Taken as a whole, the FEP list provides a centralised source of information on relevant technical and scientific considerations relating to the long-term performance of decommissioned wells, and can be used as part of systemic assessments of well safety and performance.