Blenheim field, on U.K. North Sea Block 16/21b, is the first oil field development operated by ARCO British Ltd.
The November 1990 discovery well cut 117 ft of hydrocarbon pay, which later flowed 5,700 b/d. Today, Blenheim has a sturdy floating production storage and offtake (FPSO) vessel on station.
An ARCO team worked throughout 1991 to develop Blenheim as a satellite of nearby Balmoral field's floater. "This was the obvious development route," said David Knox, ARCO's producing assets manager.
But problems in gaining access to pipelines for oil exports led ARCO to choose a stand-alone development. Knox chose an FPSO development because it offered greater than 95% uptime.
ARCO decided in October 1992 to accept a bid by Golar-Nor Offshore AS, Trondheim, Norway, for use of the Petrojarl I FPSO. A life-of-field contract for use of the ship eventually was signed in March 1994.
BLENHEIM
Blenheim field holds estimated reserves of 23 million bbl of oil. The field was developed using one vertical well and two wells with 2,000 ft horizontal sections, which are producing a combined 34,000 b/d of oil.
Petrojarl I can store 175,000 bbl of crude and handle production of as much as 45,000 b/d of oil. Produced oil is offloaded into one of two shuttle tankers, also owned by Golar-Nor, every 3-4 days.
Knox reckons the field will yield about 50% of its reserves during the first year of production because of the high productivity of the horizontal wells. Field life has been placed at 3.5 years.
Knox said first year operating costs in Blenheim field will be less than $7/bbl, although costs will rise to about $12-50/bbl by the third yea of production. ARCO's capital outlay for Blenheim development was only 12 million ($18 million), spent mainly to drill wells.
Helge Krafft, executive vice-president of Golar-Nor, said the cost of modifications to Petrojarl for service in Blenheim field was $20 million, including maintenance work.
Most recently, Petrojarl was chartered to Amerada Hess Ltd., for production of Angus field from December 1991 to June 1993 and Hudson field from July 1993 to last February After 45 days in dock for modifications, Petrojarl began producing Blenheim oil Mar. 13.
SONS OF PETROJARL
Petrojarl, now on its seventh North Sea project, has become an established option for extended production tests and small field developments. At least one similar design is to be built for Golar-Nor.
Krafft said a larger version of the basic FPSO design, known as Petrojarl IV, is to be built for $300 million for use by Golar-Nor in development of Foinaven field, West of Shetland, for BP Exploration Operating Co. Ltd.
Petrojarl Ii is a design once proposed for Heidrun field development but recently adapted for submission to BP under bidding for second phase production from Foinaven. Krafft hopes ultimately to have two FPSOs in Foinaven.
Petrojarl III is yet another version of the FPSO design, which has so f not left the drawing board. Asked about the out-of-sequence numbering system, Krafft said: "We will build only against a contract, not on spec."
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