Development and production
Development and production are the final phases of upstream oil industry activity. The majority of West of Britain operations are still in the exploration and appraisal phases, although two projects, both operated by BP, are now in the production phase. The production facility in the Foinaven field came onstream in November 1997 and the production facility in the Schiehallion field will come onstream this summer.
The production phase and environmental protection
Environmental protection measures during the production phase of an oil industry project build on the measures already put in place during the exploration phase. Extensive environmental assessments and consultation exercises were undertaken by BP before these developments were given consent by the UK Government. These processes, designed to provide effective environmental protection, addressed many of the requirements of the new Environmental Impact Assessment (EIA) Regulations required for all future developments. BP has also developed an effective oil spill contingency programme in consultation with local authorities and others groups.
Both Foinaven and Schiehallion operations are also working towards accreditation by the European Eco-Management & Audit Scheme (EMAS), which requires external verification of environmental performance, annual public reporting and continuous improvement.
Development history
The Clair and Victory fields were discovered in 1977. Block number 214/30 was found to contain hydrocarbons in 1984 and Solan/Strathmore yielded positive results in 1990. Foinaven was discovered in 1992, Schiehallion in 1993 and Suilven in 1996.
Clair is currently being worked on to define whether a commercial development is possible. However the current low oil price and uncertainties about the levels of taxation likely to be levied by the UK Government make this a tough challenge. Further appraisal will be required before any other discovery is moved forwards for development.
Foinaven and Schiehallion -- production well drilling
Before any oil can be produced from the reservoirs beneath the seabed, a number of production wells must be drilled. In Foinaven and Schiehallion, production well drilling has been enhanced by horizontal drilling. Instead of drilling vertically down through the seabed and subsurface rock into the reservoir, in a horizontal drilling operation the drill bit enters the reservoir at a shallower angle, then moves horizontally through the thin layers of oil between rock formations. This means that a larger proportion of the wellbore is in contact with the crude oil. A higher proportion of the reservoir's contents can be extracted at a faster rate, and as a consequence fewer wells are needed. Foinaven requires 14 wells rather than 28 because of this technique.
Foinaven and Schiehallion -- FPSOs
The production wells rise to a number of subsea manifolds on the seabed, which in turn are connected to rigid pipes or risers. These risers are connected to other long and flexible risers, which bring the crude oil up to a specially-built ship called a Floating Production, Storage and Offloading (FPSO) vessel on the sea surface.
FPSOs serve the same purpose as a fixed production platform. The crude oil is extracted via the production wells, subsea manifolds, rigid and flexible risers, and is then stored on board the FPSO. Every few days a shuttle tanker arrives from the nearest onshore oil terminal to uplift the crude oil from the vessel's storage tanks.
The core of the ship is a large, circular structure in the middle of the foredeck called the turret. All the control umbilicals and flexible risers connected to the subsea manifolds and production wells pass through this structure. The ship is designed to rotate around it under the influence of waves, wind and currents, and this 'weathervane' effect avoids putting any strain on risers and umbilical control cables.
There are two FPSOs in the Atlantic Margin. The Petrojarl Foinaven is owned and operated by the Norwegian company Golar-Nor, which has more than 10 years experience operating a similar vessel in the North Sea. The Petrojarl Foinaven has been on site since November 1996 and on production since November 1997. The Schiehallion was built for BP by the Harland and Wolff shipyard in Belfast and will be operated by BP staff. It has been anchored on site since April 1998 and should be on production in summer 1998.
Each FPSO has a mooring system designed to withstand a 100-year storm, as well as a supplementary thruster system for positioning -- used, for example, while latching or unlatching shuttle tankers. The FPSOs and the shuttle tankers used in Foinaven and Schiehallion also have double-skinned hulls.
This basic development concept has been used elsewhere, but the service requirements for the deep and hostile Atlantic waters have extended the use of this technology -- much of which comes from British-based contractors, who lead the world in this field.
Production in Foinaven and Schiehallion
Foinaven started production in November 1997. This year it is expected that production will increase to a rate of about 100,000 barrels of crude oil per day. There are two dedicated shuttle tankers which visit the Petrojarl Foinaven FPSO every 3 days to offload oil to the Flotta oil terminal in Orkney.
Schiehallion is working towards a production start-up this summer. It is expected to be producing about 140,000 barrels per day by 1999. The Loch Ranoch shuttle tanker will visit the Schiehallion FPSO every 4-6 days to offload oil to the Sullom Voe oil terminal in Shetland.
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