DEVELOPMENT PROGRAMS CALL FOR TWO CONCRETE PLATFORMS IN OIL, GAS FIELDS OFF NORWAY

Development plans for two fields off Norway have given a boost to use of concrete for the construction of floating production facilities. Conoco Norway Inc. let a $350 million contract for construction of the world's first concrete hull, tension leg platform (TLP) to Norwegian Contractors, Stavanger. As part of a $3.5 billion project, it will be installed in the Conoco group's Heidrun oil and gas field in the Haltenbanken area of the Norwegian Sea off mid-Norway. Heidrun is the

Dec. 23, 1991

7 min read

Development plans for two fields off Norway have given a boost to use of concrete for the construction of floating production facilities.

Conoco Norway Inc. let a $350 million contract for construction of the world's first concrete hull, tension leg platform (TLP) to Norwegian Contractors, Stavanger. As part of a $3.5 billion project, it will be installed in the Conoco group's Heidrun oil and gas field in the Haltenbanken area of the Norwegian Sea off mid-Norway.

Heidrun is the world's northernmost offshore development project.

In addition, a group led by Norsk Hydro Produksjon AS, Oslo, chose a concrete floating production platform as the basis for a $2.42 billion development of the oil province in Troll gas field in the North Sea.

Also in the Norwegian North Sea, companies involved in the Sleipner gas development project agreed to seek approval for the $1.77 billion, first phase development phase of West Sleipner reserves beginning in 1996. This will use conventional production technology, although the possibility of a concrete treatment platform has not been ruled out.

HEIDRUN PROJECT

Conoco's Heidrun TLP is to be installed in 1,100 ft of water in June 1995. First oil is expected later that year, and production will build to a peak of 200,000 b/d about 1 year later,

Heidrun, with 750 million bbl of oil and 1.8 tcf of gas, is in Block 6607-7, only 100 miles south of the Arctic Circle.

The Conoco contract comes at a crucial time for Norwegian Contractors, whose design work was criticized by a report into the sinking of the concrete substructure of the Sleipner A gas platform at the end of August.

Norwegian Contractors also faced competition from a new group hoping to break into the market for building offshore concrete structures. The group was headed by Kvaerner Engineering in partnership with the Doris group of France and Skanska of Sweden. Kvaerner holds a contract to design the Heidrun TLP topsides.

The hull contract covers design, construction, mechanical outfitting, and installation of the unit. It includes two module support beams and other engineering and coordination services.

Design work will begin immediately. Construction is scheduled at Norwegian Contractors' Hinnevagen yard near Stavanger.

The bottom section of the hull will be built in the Hinnevagen dry dock, then towed to a nearby fjord in mid-October 1993 for slipforming of the four platform legs. Module support beams will be built separately and mated with the hull, along with topside modules, in summer 1994.

The platform, with a displacement of 240,000 metric tons, will have 43 wells. Nine will be predrilled to allow rapid start-up when the platform is positioned in 1995. Predrilling will begin late in 1992.

The 354 ft high base will be anchored by four steel tethers at each corner to concrete gravity foundations on the seabed. Norwegian Contractors pioneered gravity foundations on Saga Petroleum's Snorre TLP, which is due to be installed next year.

Conoco's Heidrun TLP will be linked to an offshore crude oil storage unit that will service shuffle tankers moving oil to onshore terminals. Heidrun gas will provide feedstock for an onshore methanol plant.

Conoco, with an 18.125% interest will be operator for the development phase of the field. Statoil, with 75%, will take as operator for the production phase. Other partners are Neste Petroleum AS 5%, Norsk Hydro 1.25%, and Det Norske Oljeselskap AS 0.625%.

TROLL OIL

Norsk Hydro has submitted its Troll oil development project to Norway's Ministry of Petroleum and Energy. If approved by Storting (parliament) in the 1992 spring session, production could begin in January 1996.

Troll's oil province, underlying gas reserves in the western part of the field in Blocks 31/2 and 31/5, holds about 340 million bbl of oil. It will be produced by 17 subsea horizontal wells drilled in water depths of 975-1,035 ft.

The floating production platform will be massive, with processing capacity for 157,000 b/d of oil, 250,000 b/d of water, and 175 MMcfd of gas, which at first will be reinjected into the reservoir.

The floater will have 620,000 bbl of oil storage capacity. Oil will move through an offshore tanker loading system.

Fast track development of the floating system aims to place oil on stream about the same time as gas begins to flow from the eastern lobe of the field, which AS Norske Shell will tap with a concrete gravity based platform.

Troll, with gas reserves of 45.5 tcf, will produce as much as an average 2.06 bcfd in the first development phase. A second gas producing operation on the western lobe of the field is not expected until early in the next century.

Norsk Hydro said the development plan is designed to include later production from thin oil zones in West Troll's gas province.

A decision on whether to develop those thin layers will be made, at the earliest, toward the end of 1993 after further appraisal and evaluation.

Norsk Hydro holds a 7.7% interest in Troll. The Norwegian government has a direct equity interest of 62.8% and Den norkse stats oljeselskap AS 11.8%, with lesser interests held by Norkse Shell, Elf Aquitaine Norge AS, Conoco Norway, and Total Marine Norsk AS.

TROLL GAS

Troll gas is sold to a group of continental European utilities under a contract that includes production from 1.8 tcf East Sleipner field.

The Sleipner group, with Statoil as operator, agreed to develop 4.7 tcf of gas reserves in West Sleipner field, which also holds 302 million bbl of condensate reserves.

The plan that will shortly be presented to the Ministry of Petroleum and Energy sees the first 5 years of gas production of 566 MMcfd being recycled into the East Sleipner reservoir to enhance condensate production.

After the sinking of the concrete substructure for the East Sleipner drilling and production platform A at the end of August, the Statoil group is working all out to have a replacement unit operational to meet a contractual gas start-up date of October 1993.

Gas production from East Sleipner will build to a plateau of 630 MMcfd with 70,000 b/d of condensate. By recycling West Sleipner gas into the East Sleipner reservoir, Statoil figures an added 63 million bbl of condensate will be recovered during 1996-2001. Condensate production West Sleipner will average about 50,000 b/d.

By 2001, Sleipner partners hope to have a sales contract covering all West Sleipner volumes. The group said recycling the gas would give the flexibility to divert to sales gas production if that were required before 2001.

The development plan being put before the ministry calls for a treatment platform bridge linked to the Sleipner A unit.

This will allow use of the A platform's utilities and accommodation facilities.

In the first phase of West Sleipner, production will come from 18 wells drilled into the southern part of the field through a wellhead platform that will be linked to the new treatment platform through a 7 1/2 mile pipeline.

In the second phase of development, within 7-10 years of production start-up, facilities will be installed in the northern part of the reservoir. Total cost of development, including a compression platform at a later date, will be $2.75 billion.

West Sleipner lies in Blocks 15/8 and 15/9, where interests are Statoil 49.6%, Esso Norge AS 30.4%, Norsk Hydro 10%, Elf Aquitaine Norge 9%, and Total Marine Norsk 1%.