Phil Shaw Scott
Project Manager
Amerada Hess Ltd.
London
When Amerada Hess Ltd. (AHL) and its partners received U.K. Department of Energy approval in August 1990 for development of Scott oil field, the schedule was perceived as somewhat aggressive, if not ambitious.
Now the target of first oil by the end of 1993 looks as if it will be beaten by at least a 2 month margin. Furthermore, Scott should reach plateau production of nearly 200,000 b/d of oil within a month of first oil.
Located 130 miles northeast of Aberdeen on Blocks 15/21a and 15/22, Scott will be the largest oil field to come on stream in the U.K. North Sea this decade.
It is estimated that Scott will provide the equivalent of 10% of U.K. oil needs, with reserves of 450 million bbl of oil and 287 bcf of gas. It will make AHL third largest gross producer of oil in the U.K.
Two main factors influenced the overall approach to Scott development: safety and the desire to reach first oil and subsequent plateau production as quickly as possible.
The economics of Scott field are sensitive to when first oil is actually produced. The profitability of the field is increased by bringing sales of oil as close to construction expenditure as possible.
Therefore, to achieve rapid first oil, it was necessary to reduce the period of offshore construction, hook-up, and commissioning and predrill a proportion of the production and injection wells.
At the time of conceptual design, Lord Cullen's main recommendations with regard to offshore hardware had been largely anticipated. The maximum separation of production and drilling operations from the main utilities and accommodation facilities was desired, temporary safe haven requirements had to be achieved, and installation of freefall lifeboats was specified.
TWIN PLATFORMS
The resulting design was a two-platform, bridge-linked facility. Processing, drilling, and production facilities are all located on the larger platform structure, away from the utilities and quarters platform.
AHL decided on the North Sea's most extensive subsea development to ensure early achievement of Scott plateau production through predrilled wells.
The utilities platform contains the nonhazardous equipment, including seawater injection, power Generation, accommodation, and the main control room within the temporary safe refuge. The process platform contains the drilling package and processing equipment.
The subsea facilities comprise three manifold clusters of water injection wells, each linked to the utilities platform, and seven production wells tied back to the process platform. At first oil, seven producers and seven injectors will be operational.
Scott field is well placed for available export infrastructure. An oil export pipeline will join the BP Exploration Operating Co. Ltd. Forties system, coming ashore at Cruden Bay near Aberdeen for passage on to Kinneil oil terminal near Edinburgh for processing.
Gas will be exported through the SAGE pipeline for landfall at the new Mobil North Sea Ltd. terminal at St. Fergus.
All gas production from Scott has been sold to Mobil Gas Marketing.
Predrilling of production wells has been regarded as risky. However, Scott field had 12 exploration and appraisal wells, which allowed the reservoir to he better understood at the predevelopment stage; therefore, the risk of predrilling was reduced.
At the beginning of the development drilling phase it was estimated that Scott field covered 16,000 acres.
The total rock volume in the field would occupy a cube with sides of 1.25 km.
At plateau production, each well will produce oil at a minimum intended rate of 25,000 b/d. The platform is designed to process some 200,000 b/d of oil, with seven wells on production.
CONTRACTS
AHL selected Foster Wheeler Petroleum Development Ltd., London, as the main engineering design contractor for Scott. An estimated 1.3 million man-hr was spent by AHL and Foster Wheeler teams.
Contracts for fabrication of jackets and topsides were placed in the second half of 1990. Because of the tight schedule, several fabricators were chosen: SLP Engineering Ltd., Teesside, was responsible for drilling modules, while SLP's Lowestoft yard built the accommodation module and helideck; AMEC Engineering Ltd. and Dragados in Cadiz built the utilities deck; Belleli SpA, Taranto, built the process deck; and McDermott Scotland Ltd., Ardersier, designed, fabricated, and installed the two steel jackets.
Contracts for subsea development were awarded in parallel with the major components. Fabrication of subsea manifolds was carried out by McNulty Offshore, South Shields. Allseas Marine Contractors SA laid the export lines, and Stena Offshore Ltd., Aberdeen, laid infield flow lines. Rockwater Ltd., Aberdeen, later carried out installation, tie-in, and testing of subsea structures.
To reduce the number of man-hours worked during the offshore phase, it was decided that modules would be commissioned to the greatest possible extent onshore.
In December 1992, the drilling packages were commissioned by way of a test hole. The drilling derrick and substructure were then loaded out for transportation as a unit. Drilling equipment includes an automatic pipe handler with iron roughneck, top drive, and pneumatically operated power slip.
INSTALLATION
The production platform jacket was installed in September 1992 by the DB102 crane barge. Underleg piles were installed beforehand in preference to mud mats due to the soft sea bed.
The utilities platform jacket was in installed in March.
Twelve topsides modules were installed throughout April, with a combined weight of 32,000 metric tons. The largest of these was the 10,360 metric ton process module. The last lift on May 1 was of the two bridges linking the platforms.
The first evidence that Scott is a "plug-in" rather than a conventional hook-up project came when the platform was declared habitable in June, over 2 weeks ahead of schedule. This allowed manpower to be increased by 200 to accelerate the work program. It is expected that offshore hook-up and commissioning work will take 837,000 man-hr, compared with several million spent on other recent projects.
Final tie-in work and commissioning of subsea equipment is nearly complete.
The Glomar Arctic 1 and Sedco 707 drilling rigs are completing the seven production and water injection wells ready for first production.
Copyright 1993 Oil & Gas Journal. All Rights Reserved.
