Operating on the Frontier: Over 2 Years of FPSO Operating Experience in the Harsh U.K. Atlantic Margin
Authors: Krafft H. , Thomson R.L. 
Published: October 2008

The Foinaven field was the first offshore development to come into production in UK waters on the Atlantic Margin. The field's FPSO and subsea wells have now experienced over two years in this extremely harsh environment, including three winter seasons. This paper describes experience gained from installation, commissioning and steady state production operations, identifying the challenges encountered and solutions applied, and draws comparisons where possible between design assumptions and operating reality. The business model and performance management culture developed for efficient operation of the asset are also addressed.

Introduction

Foinaven is located in UK blocks 204/19 and 204/24a, 190km west of Shetland in water depths ranging from 400m to 600m. The field was discovered in 1992 and is estimated to hold up to 559 million barrels of oil, with the current development expected to recover 251 million barrels or more. The reservoir consists of a number of thin, areally extensive channelled Palaeocene sand bodies occurring between 2120m and 2200m subsurface. Reservoir oil is sweet with an API ravity of 26 degrees, some wax content and relatively low viscosity.

BP Amoco is licence holder for the field holding a 72% interest with Shell UK as partner. Field development was sanctioned in October 1994. Development drilling began a month later with first oil being produced in November 1997 through the Petrojarl Foinaven floating production installation, which is leased from and operated by Golar-Nor Offshore on behalf of the licence partners. The field is now operating at around 95% efficiency and is focused on continuously improving performance to deliver the required business result.

Foinaven Development Facilities

At the outset of the project, the Atlantic Margin was characterised by a lack of infrastructure. The region is also subject to severe environmental conditions, with maximum wind and waves in the region similar in magnitude to those encountered in the northern North Sea and offshore Norway. 100 year return figures indicate wind speed of 40m/s and a significant wave height of 18m, although the frequency and persistence of harsh conditions in the region result in higher average figures. Interaction of the warm Gulf Stream and cold Arctic waters, creates strong and complex currents which can reach up to 2m/s and vary greatly with water depth. The seabed is also relatively soft, accompanied by seawater temperatures which can occasionally fall below zero. Operational weather windows outside the summer season are difficult to predict and usually of short duration.

Water depths and environmental conditions in the field resulted in the selection of a floating production, storage and offloading vessel (FPSO), receiving produced fluids from an array of subsea wells on the seabed. Oil is exported by two dedicated shuttle tankers. The field layout is shown schematically in Figure 1.

The FPSO, Petrojarl Foinaven, was constructed in Spain at Astano's El Ferrol shipyard, and is owned and operated nder a production contract by Golar-Nor Offshore, a subsidiary of Petroleum Geo-Services. The 250m long vessel is the result of a radical conversion of a former Russian submarine tender, involving the fabrication of a new 142m long, 34m wide double-skinned mid-section containing storage and ballast tanks and housing the vessel's 26m diameter mooring turret.