The Dunlin oilfield is situated 195 km northeast of Lerwick, Shetland, Scotland, in block number 211/23a and 211/24a. It was originally operated byShell but was sold in 2008 and is now operated by Fairfield Energy and partners MCX. Under Fairfield initially the platform was operated using the duty holder model. Amec were the duty holder contractor and Aker Solutions was the engineering and upgrade project contract. Fairfield became the duty holder in April 2014. The Field was originally discovered in July 1973 in a water depth of 151 metres approximately 12 km from the UK-Norway median line. Estimated recovery is 363 million barrels of oil. The oil reservoir is located at a depth of 9,000 feet. Dunlin acts as the host platform for production from the Osprey and Merlin subsea fields.
Production
Production started in August 1978 from the Dunlin Alpha platform. This platform is a concrete gravity base structure of the ANDOC type. It has four legs and storage capacity for 838,200 barrels of oil. The total sub-structure weight is 225,000 long tons and it is designed to carry a topsides weight of 15,635 long tons. The storage system was decommissioned by Shell from 2005 to 2007 prior to the sale to Fairfield Energy. The topsides facilities included capability to drill, produce, meter and export oil. It also has capability to re-inject water to maintain reservoir pressure, predicted. Peak production was 115,000 barrels per day in 1979; and it was approximately in the region of 3500 - 4000 bpd in 2015 prior to the shut in announcement Oil production is by pipeline to Cormorant Alpha and then by Brent System pipeline to Sullom Voe, Shetland. Associated gas powers electrical generation. Some gas was flared.
Subsea Satellite Fields
Osprey was developed by Shell in 1989/90 and employs two drill centres, one for production and one for water injection. The drill centres are connected to the platform via two back to back flowline bundles containing 2 off 8" production flowlines and a 10" water injection line. Subsea trees and the manifolds were supplied by Cameron Oil Tools. Subsea control system was supplied by Kvaerner FSSL. The Merlin field was discovered in 1998 and was initially developed as a low cost CRINE field utilising the discovery well recompleted as a subsea producer. The Merlin drill centre was progressively expanded to 3 subsea production wells and a single water injector. The flowlines from Merlin comprise 8" water injection and production lines. These tie into the Osprey riser system at Dunlin. Merlin subsea controls tie in via a crossover manifold adjacent to Dunlin into the Osprey umbilical system. Flexible flowlines were installed for water injection service on Merlin and Osprey in 2002. Osprey and Merlin produce from the same Brent sequence geology as the main Dunlin Field.
Pipeline Infrastructure
Fairfield installed a 4" fuel gas import line from the Thistle platform in 2012 to provide fuel for the platform power generation plant. The field had become gas deficient under Shell. In an attempt to mitigate this Shell had installed a 33KVa power import cable between Dunlin and Brent C in 2002. The Brent sequence fields rely on water injection to maintain production and Dunlin had an installed water injection plant capable of delivering 250,000 bwpd supplied by 5 electrically powered water injection pumps. Dunlin acts as a pipeline node on the Brent system and provides connection point for the 16" export line from the Enquest operated Thistle and Don Fields and the 16" line from the Murchison field
Decommissioning
In May 2015, Fairfield Energy has announced plans to decommission its Dunlin Alpha platform in the North Sea. The decommissioning process, which requires regulatory approvals, is expected to cost about £400 million. Dunlin has been cited as an example of the impact a decommissioning decision has impacting surrounding infrastructure as per the 2014 Wood MER Report - the "Domino Effect". Enquest will have to provide a pipeline "bypass" to allow continued export from the Thistle complex of fields to be exported via the 16" export line into the 24" line that runs from Dunlin to Cormorant Alpha. The decommissioning of the Murchison field and the Dunlin complex removes two "shippers" from the Brent system resulting in increase pipeline operating costs for the remaining users.
