Conoco (U.K.) Ltd. has won approval from Britain's Department of Trade & Industry to develop Ganymede and Callisto gas fields in the southern North Sea.
Production is to begin in fourth quarter 1995. Gas flow is expected to average 180 MMcfd and peak at 300 MMcfd.
Ganymede and Callisto partners are operator Conoco 20%, Mobil North Sea Ltd. affiliate Superior Oil (U.K.) Ltd. 50%, BP Exploration Operating Co. Ltd. 25%, and Statoil (U.K.) Ltd. 5%.
Elsewhere in the U.K. North Sea, oil production from Piper Bravo platform resumed June 9 after a 6 week shutdown following explosions in gas flare equipment. Operator Elf Enterprise Caledonia Ltd. halted production May 2 following reports of minor explosions.
GANYMEDE
Water depth in Ganymede field is 110 ft. The reservoir, in Rotliegendes sands at 8,400 ft, is estimated to hold 250 bcf. Field fife is pegged at 20 years.
Ganymede field will be developed by a not normally manned steel platform on Block 49/22. A four legged jacket weighing 820 metric tons will have a 1,100 metric ton deck.
Platform installation is set for June 1995 by Seaway Heavy Lifting, Zoetermeer, Netherlands.
Platform design is being carried out by Brown & Root Ltd., London.
The deck and jacket will be built by McDermott Engineering (Europe) Ltd. at its Ardersier yard in Scotland.
Ganymede will be developed using five wells, yet to be drilled, plus a tieback of the 49/22-12 appraisal well. Development drilling is set to begin in July using the Neddrill 4 jack up.
CALLISTO
Callisto field lies southeast of Ganymede in the same block, where water depth is 70 ft.
The reservoir, in Rothegendes sandstone at 8,250 ft, is estimated to hold reserves of 70 bcf. Field life is estimated at 20 years.
Callisto will be developed as a single well subsea completion tied back to Ganymede platform 13 km away. The Neddrill 4 rig will tie back the 49/22-6 appraisal well in June 1995.
Callisto gas will move to Ganymede through a 12 in. pipeline. Gas from Ganymede platform will be exported through the Lincolnshire Offshore Gas Gathering System (Loggs).
An 18 in. line will run 20 km from Ganymede platform to the Loggs riser platform, from where it will be sent ashore to the Theddlethorpe, U.K., gas terminal, which was recently expanded (OGJ, Nov. 29, 1993, p. 37).
"Combining the Ganymede and Callisto production infrastructure with existing facilities at Loggs means we can keep down costs while maintaining high standards of safety and production efficiency," said George Watkins, chief executive of Conoco U.K.
"It will also enable us to develop profitably other small fields in the area that previously were thought to be uneconomic."
The Callisto control system pipeline and manifold will be designed to allow future tie-ins of gas fields. Several other prospects and reservoirs are said to have been identified or proved in the area.
Future tie-ins will depend on the outcome of development drilling in Ganymede field and on two wells to be drilled this year: an appraisal of the Europa discovery in the south portion of Block 49/22 and a wildcat on the undrilled Sinope prospect. The Thebe discovery lies in the center of the block and was appraised by the 49/228 well in 1991.
Acquisition of 3D seismic data is said to have enhanced knowledge of several other prospects, which will be evaluated in more detail.
PIPER BRAVO
Ninety-eight nonessential crewmembers had been airlifted from Elf's Piper Bravo platform to nearby installations while initial safety checks were carried out in the wake of the explosions.
Crewmembers returned to the platform May 3.
Elf engineers and U.K. Health & Safety Executive inspectors checked the gas flare system, concluding that minor repairs were necessary.
An Elf official said the repairs involved a number of small improvements, "...a bracket here, a nut there..." rather than a specific modification.
Start-up is to be sequenced during several days to reach the normal combined production of 130,000 b/d of oil from Piper and nearby Saltire field.
A Health & Safety Executive official said an improvement notice placed on the installation in May will remain in force until compliance with safety regulations have been proved.
Operations were allowed to resume after Elf submitted proposals for safe resumption of production. The improvement notice, carrying a 3 month term, is to expire in the second week of July.
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