The U.K. has flashed the green light for development of Britannia field, the largest untapped gas/condensate field off Britain.
Energy Minister Tim Eggar disclosed development approval for the North Sea field, where Chevron U.K. Ltd. and Conoco (U.K.) Ltd. will share the operator's role. Chevron and Conoco formed Britannia Operator Ltd. (BOL), a company that will concentrate on Britannia development and production.
Britannia holds estimated reserves of 2.6 tcf of gas and 140 million bbl of condensate. It will be developed under a 1.5 billion ($2.25 billion) program scheduled to start gas production Oct. 1, 1998.
Meantime, Total Oil Marine plc has started production from Dunbar and Ellon oil fields, also in the U.K. North Sea. Initial production from two Dunbar wells and one Ellen well averages 25,000 b/d. Ellon is a subsea satellite of Dunbar.
BRITANNIA PROGRAM
Britannia field development will involve an eight leg steel platform with satellite wells tied back via a subsea manifold. Peak production is expected to be 740 MMcfd of gas and 70,000 b/d of condensate.
Britannia's reservoir spreads across parts of Blocks 15/29a, 15/30, 16/26, 16/27a and 16/27b and underlies Alba reservoir, currently on stream.
Chevron-Conoco designed the project to reduce development cost from an original estimate of El.8 billion ($2.7 billion). Project director Jeff Tetlow said the project was not viable at the higher cost.
The project team cut development costs by reducing redundant equipment on the platform, using reservoir engineering to reduce well numbers, and simplifying gas processing plant design.
Development director Jim Briggs said BOL intends to reduce the development cost estimate another 10%.
This is expected to come from an alliance under which development contractors can earn increased profits for reducing costs.
FIELD COMPONENT
Britannia's platform jacket will be a 158 m high structure with 36 slots for well conductors. It will carry pipeline risers for the subsea manifold and gas and condensate export lines.
Total weight will be 19,000 metric tons.
A fabrication contract is expected to be awarded in first quarter 1995, about the same time as a contract for third quarter 1997 installation of the jacket.
Topsides will include a 10,600 metric ton integrated deck, a 4,300 metric ton drilling module, and 2,000 metric ton accommodation module. Topsides operating weight will be 28,600 metric tons.
A 57 million ($85 million) deck fabrication contract was let to Trafalgar House Offshore Holdings Ltd.,
London. Installation is slated for September 1997 under a contract to be awarded in first quarter 1995.
Last October, a 38 million ($57 million) predrilling contract was let to Sedco Forex Drilling Services Ltd., Aberdeen. The Sedco 711 and Sovereign Explorer semisubmersibles will be used for predrilling.
Beginning in April 1995, nine wells will be predrilled through a template on the jacket location. The 10 slot predrilling template is being fabricated by Lewis Offshore Ltd., Stornoway, Scotland. In May 1995, work will start on eight wells to be predrilled at the subsea manifold location.
A total 45 development wells will be required. Eighteen of these will be drilled in readiness for start-up.
The subsea manifold, which will lie 15 km west of Britannia's platform, is expected to produce 330 MMcfd out of the field's total 740 MMcfd gas flow.
The 900 metric ton manifold will house 14 well slots, of which 11 will be used and three kept free for potential satellite field tie-ins.
PIPELINES
Britannia's subsea well center will be tied to the platform using a heated flow line made up of either a coaxial 14 in. production line in a 20 in. insulated carrier plus a 3 in. diameter methanol line or a bundle with a 14 in. production line, 8 in. test line, and 3 in. methanol line within a 38 in. insulated carrier.
A 195 km, 26 in. gas export pipeline will carry Britannia gas to St. Fergus, Scotland, terminal. A 45 km, 12 or 14 in. condensate export pipeline will link Britannia to Forties field's Unity riser platform.
Preliminary engineering of pipelines will begin in January 1995, ready for procurement of materials during 1996. Installation is slated for summer 1997.
Tetlow said BOL had a choice of three options for gas processing at St. Fergus: a new terminal on a new site, a new terminal at the Total Oil Marine plc site, or major expansion of Mobil North Sea Ltd.'s SAGE system plant.
"We will make a decision on the terminal in early 1995," Tetlow said.
GAS SALES
Chevron and Conoco said most of the gas produced in Britannia's expected 30 year life had been sold to Kinetica Ltd., Mobil Gas Marketing (U.K.) Ltd., electricity generator National Power plc, and Total Oil Marine PIC.
"Britannia is the first major field to be developed where the output will be bought by private sector purchasers other than British Gas plc," Eggar said.
"This clearly demonstrates that our policy to open the gas supply market to competition will bring real benefits to the offshore industry as well as consumers."
Britannia field interests, agreed last November, are Chevron 30.2%, Conoco 27.12%, Oryx U.K. Energy Co. 9.8%, Union Texas Britannia Ltd. 9.42%, Santa Fe Exploration (U.K.) Ltd. 9.01%, Unilon Oil Explorations Ltd./Baytrust Oil Explorations Ltd. 5.49%, Texaco North Sea U.K. Co. 2.18%, Phillips Petroleum Co. U.K. Ltd. 2.12%, Fina Exploration Ltd. 1.82%, Amerada Hess Ltd. 1.76%, and Agip U.K. Ltd. 1.08%.
Dunbar development drilling is under way, which is expected to lead to plateau production of 45,000-50,000 b/d early in 1995.
The Sedco 706 semisubmersible rig is being used to help drill a further 16 wells in Dunbar. Field operator Total 33.3% and partner Elf Exploration U.K. plc 66.67% predrilled five Dunbar wells to help reduce development costs (OGJ, Aug. 15, p. 68).
Combined reserves for Block 3/14a Dunbar field and its satellites amount to 134 million bbl of oil and 920 bcf of gas.
Total also plans a subsea development in Grant field, estimated to hold reserves of 6 million bbl of oil and 220 bcf of gas. Grant is likely to go on stream in 1998.
Copyright 1994 Oil & Gas Journal. All Rights Reserved.
Issue date: 12/26/94