Thistle

Location

The Thistle and Deveron fields are situated approximately 125 miles (201 km) north-east of Sumburgh in the Shetland Isles and 275 miles (442 km) north-east of Aberdeen, UK. They are located in Block 211/18 of the UK Continental Shelf.

Discovery and Production History

• The Deveron field was discovered in 1972, and the Thistle field was discovered in 1973.
• Production from the Deveron field began in 1978, with the Thistle Alpha platform being installed in 1976 by BNOC, Britoil, and BP.
• The fields reached peak production in 1982, with 122,000 barrels of oil per day (boepd) and 36 million standard cubic feet per day (mmscfd) of gas.

Operatorship

• The operatorship of the fields has changed several times: from BNOC, Britoil, and BP, it was handed over to DNO in 2003, then to Lundin in 2004, and finally to EnQuest in 2010.

Field Details

• The oil and gas in the Thistle and Deveron fields are found within the Rannoch, Etive, Ness, and Tarbert sands.
• As of the last updates, the fields have 18 producing wells and seven water injection wells.

Thistle Alpha Platform

• The Thistle Alpha platform is a 60-slot drilling and production platform installed at a water depth of 161.5 meters.
• The platform features a conventional steel jacket with four main legs, supporting 36 modules on three deck levels.

Production and Export

• The produced oil is processed using a two-stage production separation system. The stabilized oil is metered, mixed with oil from the neighboring Dons field, and exported via a 16-inch diameter oil export pipeline to the Brent Pipeline System, which conveys it to the Sullom Voe Oil Terminal.

Field Life Extension Project (LLX)

• EnQuest initiated a major development program to extend the life of the fields. The first phase included the refurbishment of the drilling rig in 2010 and the installation of a new 30MW power generation turbine and a local equipment room on the platform in 2012.
• The second phase, sanctioned in early 2013, involved a £169 million ($260 million) investment for further development, including technology-based simplification, installation of a new process control safety system, and integrity works on the topsides and jacket.
• The LLX project aimed to extend the field's life by an additional 15 years and recover a further 35 million barrels of oil. It was expected to generate approximately 1,000 new jobs during the construction phase and was completed in 2016.

Decommissioning Activities

• EnQuest has been planning the decommissioning of certain installations, including the removal of the Crude Oil Storage (COS) tanks from the Thistle Alpha platform. These tanks, initially used for buoyancy during installation and later for crude oil storage, became redundant after the oil export route was changed. The removal is necessary due to significant fatigue damage to the tank supports, which could compromise the structural integrity of the Thistle jacket.

Current Production

• As of 2014, the combined net production rate from the Thistle and Deveron fields was approximately 7,925 boepd. The fields continued to produce oil, with new wells and well workovers contributing to the ongoing production.