Foinaven is located in UK blocks 204/19a, 204/24a and 204/25b, 190 km west of the Shetland Islands, on the United Kingdom Continental Shelf (UKCS) in water depths of between 350 and 520 metres. The field was discovered in 1990 (by the 204/24-1A well) and sanctioned in 1994. It was the first deepwater development on the UKCS and the first west of the Shetlands. First oil production from the field was in November 1997. The development has already delivered nearly twice its originally sanctioned volumes. BP operates the assets and field equity varies between the Foinaven Main Field (BP 72%, Marathon 28%), East Foinaven (BP 43%, Marathon 47%, Faroe Petroleum 10%) and T25/T35 (BP 80%, Marathon 20%) developments. Overall there are 41 wells – 25 producers, 1 gas disposal well and 15 water injectors. The subsea wells are tied back, from 5 drill centres, to the Petrojarl Foinaven FPSO (Floating, Production, Storage & Offloading vessel) via a subsea network of pipelines, control umbilicals and risers. The Foinaven reservoirs are a series of stacked basin floor submarine fan and base of slope channel sands of Palaeocene age. The sands vary in character from thinly inter-bedded fine to medium grain sandstones to massive incised channel sandstones. The Foinaven trap is both structural and stratigraphic. The structure is a faulted anticline formed as a result of compaction and inversion during Late Eocene to Miocene times. The field is dip closed along the western side.
The Petrojarl Foinaven FPSO was the result of a major conversion of the Russian submarine tender ship Anadyr at the Ferrol yard in northwest Spain during 1995 and 1996. The key part of the modification was to insert a new 142m long, 34m wide double hull centre-section with fourteen wing & double bottom ballast tanks. The result was a vessel which has an overall length of 250m and an oil storage capacity of c.250,000 bbls. Process facilities consist of two parallel oil separation and gas compression trains with a combined liquid handling capacity of 183,000 bbls per day and 110 million standard cubic feet (scf) per day of gas. Gas compression capacity is used for gas export and providing artificial lift to oil production wells (gas-lift). The optimum oil recovery mechanism requires hydrocarbon production volumes to be replaced by injecting seawater into the reservoir via dedicated water injection wells. The FPSO is free to rotate around a 26m diameter turret which is anchored to the seabed with ten mooring lines tensioned over 'springer' buoys. Eight flexible production risers, a single water injection riser, a gas injection riser and two control umbilical’s hang from the turret and provide the connection to the subsea system. Under light wind and current conditions, the FPSO (and attached tanker) 'weather vane' around the turret but during periods of high winds and currents, the FPSO utilises two propellers and a stern thruster to maintain the optimum heading and allow offloading to continue. This system has allowed extremely high export regularities to be achieved.
The subsea system provides the link between the FPSO processing facilities and the remote wells (production & injection) on the seabed and consists of:
- Flexible jumpers
- Oil production flow lines
- Gas injection lines
- Water injection lines
- Flexible risers
Crude offloading and fiscal metering facilities are installed at the stern of the FPSO and shuttle tankers hook up and load approximately every four days at current oil production rates. Two new 600,000 bbl shuttle tankers were commissioned in early 2003 (Petronordic and Petroatlantic) and transport oil directly to market in north-west Europe. Gas is exported through a 20” pipeline that links Foinaven, Schiehallion and Clair fields, via Sullom Voe Terminal, to the BP operated Magnus field.
BP is committed to sound environmental management and like all of the company's North Sea developments, Foinaven has been subject to an Environmental Assessment (EA). The EA is performed to ensure that the impact on the environment of operations is kept to an absolute minimum, this process involves undertaking studies to gain a greater insight into the environmental impacts of the development. The key distinctive physical characteristics of the marine environment in the Foinaven area are the water depth (450m), strong subsea currents (4.5 km/hr.) and low seabed temperatures (-1.5C). Key biological features include Lophelia Pertusa, a cold deep water reef building coral; Calanus Finmarchius, a herbivorous copepod which is an important source of food for juvenile fish; large numbers of seabirds during the months of May to July; cetaceans such as fin and humpback whale as well smaller toothed species such as bottlenose dolphins. Large numbers of deep water and pelagic fish are found in the area and the field lies in the vicinity of a mackerel migration and wintering area used by a large proportion of the Western Europe mackerel stock.