Chevron group plans decommissioning of Thevenard Island facilities

A group led by Chevron Corp. has submitted plans to decommission the Thevenard Island oil and gas facilities on and offshore Thevenard Island in Western Australia.

Production from the offshore fields—Saladin, Cowle, Yammaderry, Crest, Roller, and Skate—ceased in January 2014 and Chevron and partners Santos Ltd. and ExxonMobil Corp. have tried to sell the facilities without success.

The joint venture was granted a 25-hectare site on the tiny 550-hectare island 25 km northwest of Onslow and 70 km southwest of Barrow Island during the late 1980s and production began with the Saladin oil field in 1989. The other fields were progressively brought on stream during 1991-98.

The Thevenard project included three Saladin platforms in 12-18 m of water and six monopods associated with the Roller, Skate, Yammaderry, and Cowle fields in 9-16 m of water.

Subsea flowlines produced oil and gas to facilities on the island including storage tanks for oil and a tanker-loading terminal. There was also a gas export pipeline to the mainland as well as gas lift pipelines and a water injection pipeline.

Chevron plans to disconnect the subsea pipelines, but leave them in place. All the structures offshore and onshore will be removed. The 22 offshore wells and 14 directional wells drilled from onshore will be decommissioned.

The company will use a jack up rig and construction vessel with a crane for the offshore work and a workover rig for the task of plugging the wells.

It is anticipated the work will begin in 2016 and take about 12 months to complete the offshore work. Onshore decommissioning and remedial work on Thevenard, including removal of roads, footings and pathways, will take 2 years.