West Don oil field is located in blocks 211/13b to 211/18a in the northern part of the North Sea, in water depths of 170m. It is located about 150km north-east of the Shetland Islands and 12km north of the Thistle field. The oil field commenced production in April 2009, with initial peak production rates of 25,000 barrels of oil a day (bopd).
Stratic owns a 17.25% stake in the West Don field through a 50% interest in licence P1200 in the 22nd UK offshore licensing round, covering Block 211/13b.
Through licence P236 for the 211/18a block, Petrofac Energy Developments owns a 60% interest, with Valiant Petroleum owning 40% in the Don Southwest field.
The owners agreed for a fixed field unitisation, with Petrofac having a 27.7% stake in the field, First Oil expo 19.3%, Nippon Oil 18.5%, Valiant Petroleum 17.275% and Stratic 17.3%.
West Don was developed concurrently with the nearby Don Southwest field.
Geology of the North Sea oil field
The West Don reservoir comprises of a similar 470ft-thick Brent sandstone sequence to the nearby Thistle, Penguin and South Magnus oil fields.
The West Don oil field was discovered in 1975 by Burmah Oil while drilling well 211/18-9, which contained oil in Middle Jurassic Brent Group sandstones at rates of 5,000bopd. In 1976 further appraisals were made for well 211/13-4. In 1990 the third well 211/13b-11 tested oil at rates of up to 7,600bopd.
Don Southwest was discovered by BP and ConocoPhillips in 1975 and was dormant until Petrofac invested in the undeveloped field in 2006. The oil gravity of the West Don field is 34° API.
West Don oil field development and drilling equipment used
In 2007 Petrofac submitted a field development programme (FDP) for the West Don field. The development plan includes a three-well development – two producing wells and one injector, to be jointly developed along with the Don Southwest field.
With trenching of the pipelines completed, the installation of the subsea structures and diving tie-ins to Lundin Petroleum’s Thistle platform and the Brent pipeline system was also completed in 2010. Development approval was granted by the UK Government’s Department for Business, Enterprise and Regulatory Reform (BERR) in 2008. A development budget of £170m ($221.86m) was approved by partners.
The Northern Producer, with a capacity of 55,000 barrels of oil a day, has been signed as a floating production vessel. In November 2008 refurbishment works on the Northern Producer were completed in the McNulty Offshore facility in Newcastle upon Tyne. Previously, the vessel was operated for the UKCS Galley oil field.
The John Shaw semi-submersible drilling unit commenced the development wells for both fields in late July 2008.
Wells drilled as part of the West Don and Don Southwest development projects
The two West Don production wells were the first wells to be drilled. As per the FDP, the drilling of two up-dip high angle producers and one down-dip water injector well from a central cluster is complete. Development drilling commenced on West Don in 2008 and was completed by 2009.
Peak production rates and oil reserves at the North Sea fields
Production from the West Don field commenced on 28th April 2009, with initial peak production rates of 25,000bopd.
Initially oil was exported through a single anchor leg (SAL) to the offshore tanker until the Northern Producer was tied in to the Thistle platform and Brent oil export infrastructure through pipelines, for delivery at the Sullom Voe terminal, which commenced in March 2010.
The subsea flow lines between each field and the Northern Producer were installed in 2008.
Oil exports from West Don and Don SW’s Brent sandstones flows along 8in production lines to a sub-sea riser base and then to the Northern Producer. In March 2009 an additional drilling unit, Stena Spey, arrived on West Don to fasten the project.
Estimates by Stratic show the probable reserves for the West Don field at 21.5 million barrels from a STOIIP (stock tank oil initially in place) of 53mmstb. Proved reserves have been increased from 7.5 million barrels to 11.6 million barrels (two million net).
Peak production from the West Don and Don Southwest fields is expected to be in excess of 40,000bopd.