Z-Seal expandable metal sealing technology project
Re-development and lessons learned
Gordon Mackenzie - Baker Oil Tools
The Z-Seal technology is a high expansion sealing methodology replacing more traditional elastomeric sealing elements. The use of an expandable metal seal combined with a non-metallic back-up rather than an elastomer creates a high-integrity wellbore pressure seal helping to mitigate or completely eliminate many common wellbore problems encountered with the use of more commonplace elastomeric sealing methodologies. Some examples of these are the elimination of concerns re-gasification/explosive decompression, high temperature seal degradation, greater resistance to chemical attack, longevity under dynamic conditions, and lack of memory requirement for full below-gauge seal retraction.
Identifying the need
Globally, E&P companies have long sought a reliable intervention solution that could eliminate an elastomeric seal, and achieve non-monobore high-expansion deployments. The design and introduction of this technology has questioned and answered many paradigms around eliminating elastomeric failures associated with wellbore intervention sealing devices. The technology is adaptable to a broad range of wellbore conveyance methods, including threaded tubulars, coiled tubing, electric wireline, and wireline. Coiled-tubing and wireline conveyance enable metal-to-metal sealing solutions in environments where live well operations help mitigate health, safety, and environmental (HS&E) concerns, reduce non-productive time (NPT), minimize formation damage due to kill-weight fluids, and subsequently improve well economics.
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The Z-Seal technology is a high expansion sealing methodology replacing more traditional elastomeric sealing elements with metal ones.
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A major global operator identified this technology as a potential solution to their wellbore intervention challenges in a Middle Eastern offshore gas field development. The operator’s high-rate gas completions consisted of 7-in. (18-cm) monobore and 9.625-in. (24.4-cm) x 7.625-in. (19.4-cm) big bore completions with cased and perforated 7-in. liner at typical deviations of 55°. These carbonate reservoirs were initially over-pressured with significant vertical extent and having the potential for crossflow between the zones of interest. The requirement for the wells was to perform matrix rate multi-stage acid stimulations. To optimize the stimulation of the upper zones, modeling and previous field experience had shown the operator that to reduce both acid and diverter volumes, that temporary isolation of the lower zones would provide for the best solution to optimize the potential of the zone. Initial isolation of these lower zones was conducted using a traditional elastomeric sealing retrievable bridge plug. Some issues on these initial efforts relating particularly to retrieval issues based on the elastomeric element not ‘relaxing’ and on plug loss due to downward crossflow on retrieval, prompted the operator to select the Z-Seal as a platform to develop a suitable plug to meet the requirements of the operation.
Sizing and testing
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Volume 68 Issue 9
September 2008
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