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Abstract: The joint research project CLEAN is a German research and development (R&D) alliance of 16 partners from science and industry. The main theme of this pilot project is to enhance gas recovery (EGR) by injection of CO2 into an almost depleted natural gas field. The research focus is on the assessment of all processes associated with the injection. At the same time the CO2 long-term storage security of Europe’s second largest onshore gas field is analysed and evaluated. [Copyright &y& Elsevier]

Abstract: In this paper we present a new concept developed to improve the abandonment procedure of wellbores in depleted hydrocarbon fields, amongst others in Enhanced Gas Recovery (EGR) operations. The sealing concept is designed for the long-term containment of CO2 and considers the creep ability of deep Permian Zechstein salt formations in about 3,000 m depth. It is designed to amend the current standard abandonment procedure and consists of (a) an expansive gel filling in the reservoir formation, (b) a sealing element with cement extending to the impermeable caprock and (c) a salt plug as the major long-term sealing component, compatible in its composition and property to the surrounding caprock (halite). The focus of the project work described here is to develop and to model the last-mentioned long-term salt sealing element. Numerical results show that the creep ability of the mentioned salt formations can close a formerly reamed well section and hence recover the geological salt barrier with or even without using a crushed salt backfill. A field test is conducted in the North German Altmark Rotliegend gas field (Sachsen Anhalt) in order to study the technical feasibility for recovering the initial caprock integrity, to verify numerical models and to proof the sealing capability and therefore the sealing concept. [Copyright &y& Elsevier]