ABSTRACT
The assessment of the long-term integrity of an underground storage is a key factor for its operational safety and economic viability. Since the entire storage system needs to maintain its integrity throughout the operational life and beyond, an integrity assessment of salt caverns should include the borehole and its technical installations, the cavern(s) itself and the surrounding geological formation. The integrity assessment of technical well elements is standard and performed based on systematic approaches. Although there are several approaches to asses most aspects of geological formation barriers around salt caverns, there is no systematic and comprehensive approach for the geological formation barriers comparable to the assessment of the technical well elements. Therefore, we introduce a systematic approach to assess the functionality of the “geological barrier” (storage formation) and “subordinate geological barrier” (e.g. overburden) (Figure 1). The assessment is based on the evaluation of basic influencing factors (i.e. natural permeability, interactions with the cavern fluid, rock mechanical design and operating mode) that need to be considered in different scenarios to evaluate their impact on the geological barrier. All characteristics influencing the geological formation barrier are weighted and combined to generate a comprehensive statement about geological formation tightness and stability. The results can be coupled with the borehole integrity assessment and provide indications for possible measures to improve the storage integrity, to close knowledge gaps, and to identify potential weak elements of the barrier system.
