HYDRO'S TROLL FIELD TO GET CONCRETE STRUCTURE

North Sea operations continue to make news even as the area draws near a milestone with abandonment of its first producing oil field.

Here's what's happening:

Norsk Hydro AS let a 2.1 billion kroner ($310 million) contract to Kvaerner AS, Oslo, for construction of a concrete hull for the Troll oil field platform to be installed on Norwegian Block 31/2. The award follows Hydro's decision to seek bids on a steel hull design after the estimated price of a concrete hull more than doubled over the initial proposal (OGJ, Dec. 14, 1992, p. 28).

Chevron U.K. Ltd. reported encouraging results from Central North Sea appraisal well 16/26-24 in Britannia gas/condensate field. The well tested the field's oil and gas columns. Meantime, Chevron Corp.'s Dutch unit has virtually withdrawn from Netherlands with the sale of its offshore assets and most of those onshore to Dyas BV, The Hague, for an undisclosed sum.

Mobil North Sea Ltd. began production from Camelot B platform in the U.K. sector's southern gas basin. Mobil plans this year to place more gas on stream in the area.

Argyll, the first oil field on stream in the North Sea, is to be abandoned under a three field contract worth L5 million ($7.8 million) let by operator Hamilton Oil Co. Ltd., London.

TROLL PLATFORM

Hydro decided the engineering levels required to make a steel solution comparable with concrete resulted in no price advantage for steel in development of Troll field. Kvaerner will begin construction in June at its Hanoytangen yard, near Bergen.

The hull is to be finished in October 1994. Mechanical outfitting will continue until February 1995, when topsides modules will be lifted onto the hull and hooked up. Tow-out to the field is scheduled for September 1995,

Troll's platform will be the world's first catenary moored floating platform with a concrete hull. It will be 210 ft high and 330 ft square with four 95 ft diameter support columns joined at the base by pontoons.

More than 1.5 million cu ft of concrete will be used, yielding a hull weight of 145,000 metric tons. Kvaerner's dry dock will be expanded to 1,100 ft long by 380 ft wide by 55 ft deep to accommodate the hull.

The Troll oil project is part of the giant Troll field development, where production will begin in 1996 from reserves of 46 tcf of gas and 3.8 million bbl of condensate in the East Troll reservoir (OGJ, Aug. 17, 1992, p. 60).

West Troll, an oil reservoir, recently had its reserves upgraded from 345 million bbl of oil and 910 MMcf of gas to 370 million bbl of oil and the same amount of gas. Production start-up is scheduled for January 1996.

The reserves upgrade allowed the project to remain viable, despite the increased cost estimate for the hull and expansion of the field's subsea infrastructure to 19 wells from 17, Hydro said.

Current total budget for the West Troll project is 17 billion kroner ($2.5 billion), up from an original estimate of 15 billion kroner ($2.2 billion).

Planned oil production plateau is 160,000 b/d of oil, while gas flow will be 180 MMcfd. Gas will move to the East Troll platform for export to Emden, Germany.

The oil export route has not been decided. The original development plan called for offshore loading into tankers. Now a majority of the field partners want to export oil through a 16 in. pipeline to the Den norske stats oljeselskap AS terminal at Mongstad.

Partners in both Troll projects are East Troll production operator Statoil 74.576%, West Troll operator Norsk Hydro 7.688%, East Troll development operator Norske Shell AS 8.288%, Saga Petroleum AS 4.08%, Norske Conoco AS 2.015%, Elf Aquitaine Norge AS 2.353%, and Total Norge AS 1%.

CHEVRON ACTION

A 7 day test of the gas bearing zone in Chevron's 16/26-24 confirmation well, designed to establish reservoir limits, produced 17.5 MMcfd of gas and 1, 150 b/d of condensate. A second test to evaluate well deliverability flowed 35.9 MMcfd of gas and 1,750 b/d of condensate through a 14/64 in. choke.

In the oil zone beneath the gas/condensate reservoir, Chevron tested 40 gravity oil at rates of as much as 500 b/d. No further appraisal drilling is planned on the structure.

Chevron said the well cut more than 500 ft of gross reservoir with characteristics better than predicted. Net gas pay of 176 ft indicated more hydrocarbon bearing sand than expected and will increase the estimate of recoverable reserves in Block 16/26.

Chevron's sale of Netherlands assets included production interests in P/6 and Q/8a offshore gas fields and Waalwijk onshore field in Noord-Bra- bant province, along with exploration interests in offshore Blocks P/6, P/8, and Q/8 and the Eindhoven onshore permit.

Chevron retained its interest in Akkrum field in Friesland province, which it operates.

A spokesman said the Dutch assets were profitable but small and therefore not compatible with the company's business strategy.

Chevron's share of production from the Dutch fields was 6.1 bcf of gas in 1990, while its share of reserves was estimated at 72 bcf. Akkrum's reserves are placed at 9 bcf of gas.

The sale allows Chevron to concentrate on core assets, including production in the U.K. sector and exploration projects in Yemen, Albania, and Italy.

MOBIL PRODUCTION

Mobil's Camelot B platform, an unmanned, remote controlled unit, is producing 25 MMcfd from a single well that taps reserves estimated at 33 bcf. Production moves via pipeline 6 miles to Leman gas field, then 30 miles to shore where it is processed for sale to British Gas plc.

The Camelot B reservoir, a 1989 discovery held 100% by Mobil, ties on Block 53/2, about 4 miles from the company's Camelot platform.

Mobil stepped up its southern basin production last November when it placed an average 21 MMcfd on stream from Tristan field. Later this year Mobil's Lancelot and Guinevere fields will start up, yielding the company another 56 MMcfd on average.

ARGYLL ABANDONMENT

Hamilton's Argyll field, in U.K. North Sea Block 30/24, went on stream in 1975 from reserves then estimated at 25 million bbl of oil. Argyll, along with Duncan and Innes fields in the same block, which also are to be abandoned, produced more than 97 million bbl of oil during 17 years.

Stena Offshore Ltd., Aberdeen, won the abandonment contract, which involves work on 18 subsea wells. The fields were developed using floating production systems built around converted semisubmersible rigs. Argyll had the world's first floating production system (OGJ, Dec. 14, 1992, p. 26).

The Stena Wellservicer vessel is on location preparing for abandonment, recovery of wellheads, and debris clearance. The Stena Seawell is due on location soon to begin downhole work. Stena said abandonment will require 4 months.