D5.5 - Qualitative assessment of potential risks, Zalecze & Zuchlow site

Danijela Sijacic, Merel Schelland & Ton Wildenborg

The objective of the study was to perform a qualitative risk assessment of CO₂ storage in the Zalecze-Zuchlow gas reservoirs using a scenario approach. A qualitative scenario analysis is the first and necessary step in the hazard assessment of a CO₂ storage site. The main goal of this step was to identify the relevant CO₂ release scenarios and provide a first indication of their importance for the site.

The process of identifying leakage scenarios was facilitated by a database of Features, Events and Processes (FEP). FEPs describe characteristics and behaviour of the geological and engineering systems which are relevant to safety.

Five experts participated in the completion of the online questionnaires and the pre-selection of FEPs for the workshop. All together, they selected FEPs, of which reactivation of faults, well integrity attack and formation enhancement (fracking, acid jobs) were chosen three times, and the other FEPs, concerning seal integrity, connected to fault integrity, linked to well integrity, and concerning the storage system as a whole; the so-called system-level FEPs) one or two times. These FEPs were discussed during the workshop, which was attended by ten experts from various fields and organizations, besides the three facilitators from TNO. During the discussions on fault and seal integrity, it became apparent that the FEPs connected to failure of these components could be neglected after all. No fault or seal leakage scenarios were hence to be defined.