Successful Delivery of Deep Water Subsea Developments in the UK Atlantic Margin
Authors: Smith T.P.D. , Pettigrew G. , Worsley M.T.C. , Walls B.R. , Clark E. , Brookes D.A. , Wood D.G. 
Published: October 2008

Abstract
This paper will provide an overview of the delivery from concept into production of subsea portion of the Foinaven and Schiehallion developments, BP Amoco's first deepwater projects West of Shetland. The paper will outline some of BP Amoco's previous experience of subsea developments and the new challenges faced West of Shetland. The contracting strategy adopted at the beginning of the projects will be described as will the organisation, communications and relationships which they fostered. A brief summary of the technical features of the subsea systems will be provided. Some key technical lessons learnt on both projects will be discussed and the major benefits of capturing and sharing this learning will be demonstrated. As part of this process the paper will demonstrate the importance of risk management and technical integrity assurance processes towards achieving a successful outcome. The paper will conclude with a review of the subsea issues and general lessons learnt from these projects, which are being carried into future BP Amoco developments.

Introduction
In 1992 BP Amoco and its partner Shell, discovered the Foinaven oilfield in 500 metre water depths approximately 150km west of the Shetland Islands on the UK Continental Shelf. The following year, and only 10km from Foinaven, the Schiehallion oilfield was discovered in 400 metres of water and covered blocks licensed by BP Amoco/Shell and Amerada Hess/Statoil/Murphy/OMV. In 1994 a smaller oilfield Loyal was discovered in the BP Amoco/Shell block just to the north of Schiehallion. This string of successes was quickly identified to be of sufficient size to have commercial potential, subject to the generation of appropriate field development plans.

Challenges
In considering the development options two main challenges had to be faced;

Metocean Conditions.
Whilst wave heights in this area are only slightly higher than in the Northern North Sea, the seasonal difference between the summer "weather window" and the winter period is much more marked. Any operations performed in winter months would be subject to significant weather downtime. The area was also noted for frequent and unpredictable high currents which had caused operational problems and equipment failure in previous exploration drilling campaigns. Construction methods would have to be suitable for use in as high a sea state as possible if long periods of non productive work were to be avoided. Details are provided in Ref. 1.

Deep Water.
From early field development studies it was clear that some form of floating production system (e.g. TLP or FPSO) would be necessary. Given the water depths and severe metocean conditions, fixed jackets would not be practicable. Also given the area covered by the fields some level of subsea production would be required, at least for satellite tiebacks if not for all production. Furthermore due to the water depths, all subsea construction work would have to be carried out without the use of divers.