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OTO 061/2001

Completion component reliability - Failure mode identification

A study has been undertaken to determine the credible failure modes and their direct effects as associated with typical single and dual completion gas lift designs as utilised in the UK North Sea, with the understanding that both wellhead configurations would be analysed under normal operating conditions. No consideration was given for any installation, workover or abandonment activities in connection with the wells. To ensure that a typical wellhead and tree arrangement was modelled, vendor information in the form of general arrangement drawings and associated information was reviewed from various manufacturers. A representative single and dual completion model was generated from this information in conjunction with the expertise associated within the project team. In order to identify the key components and seal arrangements that required consideration during the FMECA, the primary gas path was charted for both representative models. Each model was then broken up into zones to help facilitate the FMECA. Primary, secondary and tertiary barriers (where appropriate) were then identified. With the aid of zone specific drawings the FMECA was carried out for each representative model. The FMECA was carried out up to the side pocket mandrels in the production tubing for completeness, however, the main focus of the study was above the dual bore upper packer separating the upper and lower A annulus. The results of the FMECA for the single and dual completion model are detailed in Appendix F & E respectively. Both FMECA's highlighted failure modes with the potential to leak injection gas to the atmosphere. Further leak sources were identified arising from component/sealing arrangement failures. These failures could in turn, cause injection gas to leak into the B annulus and C annulus (single completion only).

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Updated 2010-03-19