Norway - Troll

[Administrator]

In April 2020, the world's largest pipelaying vessel, the Solitaire, completed laying 26 kilometres of new pipeline between the Troll A platform and the new subsea installations of the Troll Phase 3 project. It's our most profitable project ever, with a break-even of just USD 10 per barrel.

The Troll field lies in the northern part of the North Sea, around 65 kilometres west of Kollsnes, near Bergen.
The field comprises the main Troll Øst and Troll Vest structures in blocks 31/2, 31/3, 31/5 and 31/6.

Containing about 40 per cent of total gas reserves on the Norwegian continental shelf (NCS), it represents the very cornerstone of Norway's offshore gas production.

Troll is also one of the largest oil fields on the Norwegian continental shelf. In 2002 the oil production was more than 400,000 barrels per day.

Equinor operates the Troll A, B and C platforms and the landfall pipelines, while Gassco is operator for the gas processing plant at Kollsnes on behalf of Gassled. Equinor is technical service provider for Kollsnes operations.

The enormous gas reservoirs lying 1,400 metres below sea level are expected to produce for at least another 70 years.

Development


Troll is a field in the northern part of the North Sea. The water depth is 300-330 metres. Troll was discovered in 1979, and the initial plan for development and operation (PDO) was approved in 1986. The plan was updated in 1990 and involved the transfer of gas processing to the Kollsnes terminal. The production started in 1995. 

A phased development was pursued for the Troll field, with Phase I recovering gas reserves in Troll Øst and Phase II focusing on the oil reserves in Troll Vest. Troll Phase I has been developed with Troll A, which is a fixed wellhead and compression platform with a concrete substructure. 

Troll A receives power from shore. The gas compression capacity at Troll A was increased in 2004/2005, and again in 2015. Troll Phase II was developed with Troll B, a floating concrete accommodation and production platform, and Troll C, a semi-submersible accommodation and production steel platform. The oil is produced from several subsea templates tied-back to Troll B and Troll C by flowlines. The production from Troll C started in 1999. 

The Troll C platform is also utilised for production from the Fram field. Several PDO amendments were approved in connection with various subsea templates at Troll Vest. A PDO for Troll Phase III (gas production from Troll Vest) was approved in 2018 and the production started in 2021. An amended PDO for power from shore to Troll Vest was approved in 2021, and both Troll B and Troll C have been operated partly with power from shore since 2024.

Reservoir

Troll contains very large amounts of gas resources and is also one of the largest oil producing fields on the Norwegian continental shelf. The field has two main structures: Troll Øst and Troll Vest. About two-thirds of the recoverable gas reserves lie in Troll Øst. 

The gas and oil reservoirs in the Troll Øst and Troll Vest structures consist primarily of shallow marine sandstone of Late Jurassic age in the Sognefjord Formation. Part of the reservoir is also in the underlying Fensfjord Formation of Middle Jurassic age. The field consists of three relatively large, rotated fault blocks. The eastern fault block constitutes Troll Øst. The reservoir depth at Troll Øst is 1330 metres. Pressure communication between Troll Øst and Troll Vest has been proven. Originally, the oil column in Troll Øst was mapped to be 0-4 metres thick. 

A well drilled in 2007 proved an oil column of 6-9 metres in the Fensfjord Formation in the northern segment of Troll Øst. The Troll Vest oil province originally had a 22 to 26-metre-thick oil column under a small gas cap, located at a depth of 1360 metres. The Troll Vest gas province originally had an oil column of 12-14 metres under a gas column of up to 200 metres. The oil column is now reduced to a thickness of only 1 to 5 metres. A significant volume of residual oil is encountered directly below the Troll Vest oil column.

Recovery strategy

The gas in Troll Øst is recovered by pressure depletion through 39 wells drilled from Troll A. The oil in Troll Vest is produced from long horizontal wells, which penetrate the thin oil zone directly above the oil-water contact. The recovery strategy is based primarily on pressure depletion, but this is accompanied by a simultaneous expansion of both the gas cap above the oil zone and the underlying water zone. Some gas is also reinjected. Produced water was reinjected into the northern part of the Troll Vest oil province from 2000 to 2016.

Transport

The gas from Troll Øst and Troll Vest is transported through three multiphase pipelines to the gas processing plant at Kollsnes. The condensate is separated from the gas and transported by pipeline to the Mongstad terminal. The dry gas is transported in Zeepipe II A and II B to Zeebrugge in Belgium. The oil from Troll B and Troll C is transported in the Troll Oil Pipelines I and II, respectively, to the oil terminal at Mongstad.

Status

More than two million reservoir metres have been drilled on Troll. Drilling of new oil production wells on Troll concluded altogether; however, the need for future oil wells will be considered regularly. Various measures have been implemented and are in the preparation phase to improve gas capacity and production, such as drilling of several new gas wells in the coming years. A new gas export solution from Troll B to the Kvitebjørn gas pipeline started operation in 2025.

PROVEN IN 1979

Norske Shell was chosen as operator when block 31/2 was awarded in April 1979. A large gas find with an underlying oil zone was proven later that year. The block was declared commercial in 1983.

The neighbouring blocks were awarded to then Statoil, now Equinor, Norsk Hydro and Saga Petroleum in 1983.

Block 31/2 contains 32 per cent of the Troll field's reserves, while the remaining 68% lies in the three other blocks.

The licence terms for block 31/2 specified that Equinor could take over as operator for this acreage eight to 10 years after a discovery had been declared commercial.

In 1985, the two licences were unitised so that Troll could be developed as a single field.

Equinor took over as production operator for Troll Gas on 19 June 1996, while Hydro started production from Troll Oil in the fall of 1995.

TROLL GAS

Troll Gas comprises the Troll A platform, the Kollsnes gas processing plant west of Bergen and the pipelines between the platform and the land plant.

Norske Shell was responsible for the first gas development phase on Troll, which received a green light from the Norwegian parliament (Storting) in December 1986. Four years later, we agreed with Shell to move the processing facilities originally due to be installed on the A platform to a plant on land at Kollsnes west of Bergen. This made it possible to build a simpler offshore gas production installation than originally planned, with smaller staffing.

Troll A is the tallest structure ever moved by humans over the surface of the Earth. Its concrete support section has been built for a producing life of 70 years. The platform is the only one of its kind on the NCS that is powered electrically from land.

We took over as operator for Troll Gas from Norske Shell on 19 June 1996 with gas coming on stream in the first half of that year, marking the completion of the gas development. Contractual gas deliveries began flowing from the field to continental Europe under the Troll gas sales agreements on 1 October 1996. Initial deliveries under these contracts, which began on 1 October 1993, were provided from our Sleipner Øst development in the North Sea.

Declining pressure in the Troll reservoir means that more compression is needed to help drive gas production through the pipelines to the processing plant at Kollsnes. Two compressors have accordingly been installed on the A platform, and new technology allows these units to be powered from land. That in turn means zero carbon dioxide and nitrogen oxide emissions from the installation or the processing plant.

TROLL OIL

Troll B, a floating process and accommodation platform with concrete hull, and Troll C, a floating process and accommodation platform with a steel hull, produce from thin oil-bearing layers in the Troll Vest reservoir.

The thin oil layer is between 22 and 26 meters in the Troll Vest oil province and 11 and 13 meters in the Troll Vest gas province. In order to recover oil from the thin layer, it has been necessary to develop advanced drilling and production technology.

All of the more than 110 production wells to be drilled in Troll Oil are horizontal wells. This entails drilling in two phases. First, down to the reservoir, which lies at 1,600 meters beneath the sea bottom, and then to 3,200 meters in a horizontal direction through the reservoir.

A total of 28 of the wells are called multi-lateral wells, which have two or three horizontal sections that radiate out from a conjunctive point in the reservoir.

Location: Blocks 31/2, 31/3, 31/5 and 31/6 in the North Sea
Production start: Troll Oil, 19 September 1995
Production: Oil and gas