Technology at Work: Assessing tubular connection leakage integrity ///
Casing / tubing strings used in almost all oil/gas wells employ threaded connections which are expected to provide both structural and leakage integrity under service loads. The risk of a casing or tubing string leak increases with well depth, i.e., number of connections; and a significant leak from even a single connection can constitute a completion failure. Connection leakage or failures can lead to serious economic / safety consequences, including: sustained casing gas pressure; exposure of unprotected equipment to corrosive fluids; external pressure buildup leading to casing collapse; and abandonment concerns. These problems are most critical in HPHT / sour wells; and offshore platform or subsea wells.
As loading conditions associated with deeper, more hostile well environments have increased tubular string performance requirements, many operators switched from using standard API connections, i.e., 8-rd or buttress thread profiles, to premium connections. Whereas the sealing of API connections relies on thread compound blockage of the inherent helical leak path through the threads, premium connections incorporate mating seal surfaces in pin / box components which are pre-stressed during make-up to provide a direct seal mechanism. There is a wide range of premium connection products currently available for different well applications, although designs vary considerably and are typically proprietary.
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