Schiehallion

Schiehallion Oil Field Project Profile

The Schiehallion oil field is located approximately 175 kilometres (110 miles) west of the Shetland Islands in the North Atlantic Ocean, within the UK Continental Shelf blocks 204/20, 204/25a, 204/25b, 205/16, and 205/21b.
The field is situated in water depths ranging from 350 to 450 metres (1,150 to 1,480 feet).

The Schiehallion oil field was discovered in 1993 by the semi-submersible drilling vessel Ocean Alliance while drilling the third exploration well in block 204 (well 204–3).
An appraisal of the Schiehallion and adjacent Loyal field was conducted during 1994 and 1995, culminating in a successful extended well test. The combined development of the Schiehallion and Loyal fields was sanctioned in April 1996.
Oil production started on 29 July 1998.

The project is operated by BP, with partners including Shell, Amerada Hess, Murphy Oil, Statoil, and OMV. The ownership percentages are approximately: Shell - 55%, BP - 33.5%, and OMV - 11.8%.

The estimated recoverable oil reserves for the Schiehallion field are between 340 million and 600 million barrels, with additional reserves from the Loyal field. Total recoverable reserves are estimated to be around 425 million barrels, including both fields.
Peak production is approximately 154,000 barrels of oil per day, with the Schiehallion field contributing around 117,000 barrels per day and the Loyal field contributing around 25,000 barrels per day.
The fields have produced nearly 400 million barrels of oil since production began in 1998, and an estimated 450 million barrels of resource are still available.

The field is developed using 29 seabed wells in four drilling centres: Schiehallion Central, Schiehallion West, Schiehallion North, and Loyal. These wells include 16 horizontal production wells and 12 non-horizontal water injection wells, along with one gas disposal well.
The subsea layout includes manifolds, steel pipelines, and flexible risers that transport the production fluids to the FPSO vessel. The largest drilling centre, Schiehallion Central, has nine production wells and four water-injection wells.

The Schiehallion FPSO is one of the world's largest new-build vessels of its type, capable of storing 950,000 barrels of oil. It was designed and constructed by the Atlantic Frontier Alliance, a consortium including Harland and Wolff, SBM Offshore, and Brown & Root.
The FPSO has a processing capacity of 200,000 barrels per day and is moored by a top-mounted internal turret (TMIT) system, allowing it to weathervane around its anchored position. The vessel is anchored using 14 anchor legs.
The FPSO incorporates two trains of oil separation and high-pressure gas compression. Oil can be off-loaded onto shuttle tankers at a rate of 600,000 barrels per 24-hour period.

After more than a decade of operation, the original Schiehallion FPSO was decommissioned in 2013 due to deteriorating operating efficiency and the need for significant maintenance. This led to the Quad 204 Redevelopment Project, which involves a new-build FPSO vessel (the Glen Lyon), additional wells, and the expansion of the subsea infrastructure. This redevelopment aims to extend production beyond 2035.

The decommissioning of the original Schiehallion and Loyal fields infrastructure began in 2013 as part of the Quad 204 Redevelopment Project. The decommissioning plan includes the removal of installations and pipelines, with some facilities being reused or left in situ for potential future use.