Thistle and Deveron fields are located 125 miles (201km) north-east of Sumburgh in the Shetland Isles and 275 miles (442km) north-east of Aberdeen, UK, in Block 211/ 18. The distance between the two fields is about 3km. Enquest holds a 99% interest in the fields and BP holds 1% interest.
Oil and gas at the two fields are found within Rannoch, Etive, Ness and Tarbert sands.
Thistle / Deveron fields discovery and production
The Deveron field was discovered in 1972 and the Thistle field in 1973. The Thistle Alpha platform was installed in 1976 by BNOC, Britoil and BP. The operatorship was handed over to DNO in 2003, then to Lundin in 2004, and finally to EnQuest in 2010.
Production from the Deveron field started in 1978 with 43 producing wells and 15 water injection wells. The oil and gas production peaked in 1982 at 122,000 barrels of oil per day (boepd) and 36 million standard cubic feet a day (mmscfd) of gas. In 1984, oil production from the Deveron field, which was developed using four deviated wells drilled from the Thistle platform.
Field life extension project details
A major development programme to extend the life of the fields was initiated by Enquest soon after it took over the operatorship. The first phase of the Thistle Late Life Extension (LLX) project included the refurbishment of the drilling rig in 2010. A new 30MW power generation turbine and a local equipment room on the platform were installed in 2012.
EnQuest sanctioned the second phase of the LLX project in early 2013 after it secured a brownfield tax allowance (BTA) and approved a £169m ($260m) investment for further development of the fields. It involves a technology-based simplification and streamlining of processes, installation of a new process control safety system, several topsides and jacket integrity works.
Upon completion in 2016, the LLX project will extend the life of the field by an additional 15 years and is targeted at recovering a further 35 million barrels of oil from the Thistle and Deveron fields. The current project is expected to generate approximately 1,000 new jobs during the construction phase.
Production from Thistle / Deveron fields
The SFB-P1 well, the first in more than 20 years, came into production in 2010 as a result of the development activities. As of November 2014, five new wells were completed, three of which include electric submersible pumps, well workovers and partial well abandonments.
The fields produced at a combined net rate of 4,836boepd in 2010. The production rate increased to 5,436boepd in 2011 and to 8,058boepd in 2012. Net production from the fields in 2013 was 7,925boepd. The Thistle / Deveron fields currently have 18 producing wells and seven water injection wells.
Thistle Alpha platform details
The Thistle Alpha platform is installed at a water depth of 161.5m. The 60-slot drilling and production platform features a conventional steel jacket with four main legs, which supports 36 modules on three deck levels.
Oil exportation facilities
The produced oil is processed using a two-stage production separation system and the stabilised oil is metered, mixed with the oil produced from the neighbouring Dons field before being exported via a 16in-diameter oil export pipeline to the Brent Pipeline System, which further conveys it to the Sullom Voe Oil Terminal.
The Northern Leg Gas Pipeline (NLGP) system supplies the fuel gas required for powering the platform.
Contractors involved with the field life extension project
Operations and maintenance works at the site are performed by Petrofac, on behalf of Enquest. Drilling activities at the project site are being assisted by KCA Deutag and Aker Solutions. The life extension options for the project were reviewed and analysed by Xodus Group.
Nortech Solutions has been contracted to carry out the process simplification works on the platform. Pyeroy Group and Walker Technical Resources are performing the topsides integrity work by refurbishing the platform’s four stair towers.
The contract for the entire structural inspection activities, including certain repair and maintenance operations for the platform, has been awarded to Halline Marine. Schlumberger Artificial Lift deployed its REDA Maximus electrical submersible pump (ESP) technology for one of the new wells at Thistle in 2011.
The new riser system of the platform was designed by MCS Kenny. The design and construction safety reviews, including installation of a new gas turbine generator package exhaust stack and support tower on the platform, were performed by Derrick Services.
A new fresh water maker for the platform was supplied by Salt Separation Services. The upgrade to the rating capability and functional distribution of a high-voltage (HV) feeder panel as part of the overall site HV switchboard was performed by Melton Power Services.
A new 36t, A60 rated local equipment room module was supplied by Aiken Group. Custom Consoles supplied a customised SteelBase desk and auxiliary furniture for the engineering control room of the platform.
Kentz Cranes supplied two identical 60t diesel-hydraulic boom hoist cranes for the platform in late 2013. The installation and maintenance works for the cranes are being performed by Sparrows Group. Other key players involved in the project are Fabricom Offshore, Opus and Peak Global Consultancy.