Foinaven and Schiehallion/Loyal are the first oilfields West of Shetland (WoS). They were developed using Floating Production, Storage and Offloading (FPSO) technology in water depths of between 350m and 550m and arguably the harshest environmental conditional yet experienced offstore.Traditional project time scales were halved by shortening and overlapping the reservoir and facilities developments. This paper describes some of the challenges faced by the geotechnical engineers working on these project and summarises lessons learnt from site investigates and the design and installation of foundations and anchors.
This paper is about three hydrocarbon discoveries WoS, Foinaven, Schiehallion and Loyal, which BP Exploration Operating Company (BXP) and it partners have developed using FPSO systems (Figures 1 and 2).
Foinaven is on the continental slope about 150 km due west of the Shetland Islands in water depths of between about 350m and 550m. It was discovered in 1992, sanctioned in late 1994 and began producing oil in November 1997. The expected field life is about 12 to 15 years. The cost of the development is about 11 billion.
The Schiehallion and Loyal Fields are approximately 15km to the east north east of Foinaven in water depth between 350m and 470m. They were discovered in Autumn 1993 and late 1994, respectively. A $1.5 billion combined-field development began in 1995 and First Oil is expected in 3Q 1998. The design life of the field is 20 years.
Reservoir appraisal and engineering design and construction are phased in conventional oil field developments. The reservoir and engineering activities were shortened and overlapped for the two WoC prospects (so-called Parallel Engineering) and despite the absence of existing oil infrastructure and very severe environmental conditions they were completed in about half the traditional time. This paper describes the geotechnical challenges posed during these pioneering field developments, including the lessons learnt during the site investigations and from the design and installation of foundations and anchors.
The Foinaven and Schiehallion/Loyal developments are similar, Each comprises discrete clusters of well (called drill centres), connected through manifolds to flowlines which run over the seabed to flexible pipe (risers) ascending to a permanently stationed FPSO vessel. Crude oil is periodically off-loaded from the FPSO by shuttle tanker and transported to a suitable terminal.
The Foinaven development comprises six sites spread over an area if about 12km by 7km of seabed (Figures 2 and 3). It has two main drill centres, DCI and DC2A, When fully operational each of these drill centres will have eight production well and four and one water injection wells, respectively. There are also two remote water injection sites WWI and EWI and one remote gas injection well site called ?An?Tecallach?. A third production drill centre, East Fornaven, is being considered.
The Schiehallion and Loyal development has a similar size footprint to fornaven. It comproses four main drill centres: Central West; North and Loyal as shown on Figures 2 and 4. Each has production and water injection wells except for Schiehallion North which is for water injection only