Oil company Nexen has submitted a decommissioning plan for two of its oilfields in the UK North Sea.
Nexen, based in Canada, delivered a decommissioning program for its Ettrick and Blackbird fields located in blocks 20/2a and 20/3a of the UKCS in the Outer Moray Firth, in approximately 115 meters water depth.
Both fields were predominantly oil reservoirs, produced via subsea wells tied back to the FPSO Aoka Mizu. The Aoka Mizu was operated by Bluewater on behalf of Nexen.
Nexen, a subsidiary of the Chinese oil company CNOOC, said that it had investigated various alternative production strategies to extend the life of the Ettrick and Blackbird fields, but no viable alternative to decommissioning has been identified.
Among options considered by Nexen were Tie-back to Buzzard platform, review of FPSO market, alternative Production Facilities, e.g. unmanned / normally unmanned production buoy, however Nexen said the alternatives proved to be uneconomic.
Thus, cessation of production from the Ettrick and Blackbird fields was approved on the June 1, 2016.
The FPSO has been disconnected and removed from the field. Flowline and umbilical flushing activities were completed from the Aoka Mizu in late June 2016.
All Xmas Trees were disconnected from the subsea infrastructure, with blind flanges fitted and pressure tested. Xmas Tree disconnection works were completed on the 11th of July 2016. The FPSO sailed from the field on the 1st of August 2016, and is currently berthed in Gdansk awaiting future redeployment.
Nexen’s decommissioning program, unter review by the UK authorities, entails FPSO moorings will be recovered to shore; Subsea equipment will be recovered to shore and piles cut to -3 metres; All buried pipelines and umbilicals will be left in situ, with end sections cut and recovered to shore.
Decommissioning activities are expected to start in the first quarter of 2017, with full decommissioning works including post-decommissioning survey, slated for completion in 2022.
Nexen’s plan is being reviewed by the Department for Business, Energy and Industrial Strategy (BEIS) (formerly the Department for Energy and Climate Change (DECC)), which regulates decommissioning of offshore oil and gas installations and pipelines in the UK.
Offshore Energy Today Staff