Clair oilfield
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The Clair oilfield is the largest discovered but undeveloped hydrocarbon resource on the UK Continental Shelf. The field is located 75km west of Shetland in water depths of up to 140 m and extends over an area of some 220km², covering five licence blocks - 206/7; 206/8; 206/9; 206/12 and 206/15.
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[edit] Discovery
The Clair reservoir was discovered in 1977, with the 206/8-1a exploration well penetrating a 568 m oil column in a thick sequence of Devonian to Carboniferous continental sandstone.
[edit] Reservoir Appraisal
Between discovery and the late 1980's ten appraisal wells were drilled. This activity demonstrated that the structure extended to an area of some 400km² with static oil-in-place, although it failed to confirm the presence of economically recoverable reserves.
Two further wells were drilled in 1991, two in 1992 and one in 1995. Two of these wells (206/8-8 and 206/8-9z) demonstrated the potential for commercial flow rates but were not produced for long enough to give confidence in long term reservoir deliverability.
In 1996 there was a breakthrough in the drilling and extended well testing (EWT) of 206/8-10z well. The EWT was followed by the side-tracking of an offset well into the pressure sink created by the EWT. The 1996 well test results set the scope for the 1997 drilling programme and triggered interest in a first phase of development.
Two further wells were drilled in 1997 to appraise the 'Graben' and '3A' segments to reduce uncertainty in these areas adjacent to the core area.
In May 1997 it was agreed by the Clair partners to jointly develop the field. BP was appointed as the operator and programme coordinator. The Clair Partnership comprises five partners with the following fixed equity interests:
- BP - 28.6%
- ConocoPhillips - 24.0%
- Chevron - 19.4%
- Enterprise - 18.7%
- Amerada Hess - 9.3%
[edit] Field Development
Development of the Clair field will be a 'phased development'. The first phase will target the 'Core', 'Graben' and 'Horst' segments of the southern area of the reservoir, which have 1.75 billion barrels (278,000,000 m³), of which 250 million barrels (40,000,000 m³) can be recovered.
It is planned to drill 15 producing wells, eight water injectors and one drill cuttings re-injection well. Plateau production is expected to be 60,000 bbl/d (9,500 m³/d) of oil and 20 million cubic feet (570,000 m³) of gas per day.
Further development phases will be dependent on the success of Phase 1.
[edit] Development Concept
The design comprises a fixed platform with production and process topsides supported by a steel jacket.
BP awarded the contract for the fabrication of the platform jacket to Aker Verdal. The jacket is a four-legged single steel structure. At its base, the jacket measures 45 m x 50m, has a height of 169 m, and a total weight of 8,800 tons.
The contract for the construction of the platform topsides was awarded to AMEC. There will be additional processing facilities for offshore power generation, water injection, produced water and cuttings re-injection, surplus gas disposal (export or re-injection) and flare gas recovery. Artificial lift is provided for all producing wells with the option of Electric Submersible Pumps (ESPs) for future wells intervention and the operations will feature simultaneous drilling and coil tubing well intervention operations (SIMOPS). The topsides deck (including the flare boom) weighs 10700 tonnes.
The contract to build the accommodation modules was awarded to Leirvik Module Technology. The accommodation contract involves the fabrication of the living quarters and utility building, which will form part of the topsides for Clair and have a weight of 1000 tonnes.
The contract for the drill rig fabrication contract was awarded to Heerema Hartlepool. The scope of the fabrication work incorporates fabrication of a Derrick Equipment Set (DES) module, with substructure and skid base and a Drilling Support Module (DSM). The work includes equipment installation and extended commissioning and the modules weigh approximately 2000t and 2400t respectively.
The entire structure will have a design life 25 years.
