Twenty years of oil production from Troll

This week it is 20 years since the start of oil production from the Troll field, in the northern part of the North Sea, around 65 kilometres west of Kollsnes, near Bergen, Norway. 

According to its operator, Statoil, the 20 year-old can look back on enormous wealth, with 1.56 billion barrels produced so far and NOK 460 billion ($54.21 billion) in income.

Statoil 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. Statoil is technical service provider for Kollsnes operations.

“Troll oil is the impossible made possible. Only a few believed in extracting the thin oil zone at Troll, and through a burning desire to make it happen, determination and innovation, Troll oil became reality,” says Øivind Dahl-Stamnes, head of Troll production.

Determination and innovation in reservoir technology, drilling, well and seabed technology and professional and systematic operations have taken Troll Oil to where it is today: Norway’s biggest oil producer the last three years, Statoil emphasized.

“Troll oil is a story that summarises the best our operations and the opportunities on the Norwegian continental shelf,” Dahl-Stamnes continues.

A well technology puzzle

The Troll oil and gas adventure started with the awarding of the fourth licensing round in 1979. On July 17, 1979, Borgny Dolphin started exploration drilling, and four months later Troll was a fact.

A thin oil-bearing layer stretches across the entire field, but is only viable in two provinces in Troll west. The oil is produced using 15 seabed frames with a total of 121 well slots linked to the floating production platforms Troll B and Troll C.

The greatest challenge when planning the field was to develop technology to extract the thin oil zones without the wells producing too much gas. Technology was challenged and resolved, and in many ways Troll has been groundbreaking in drilling and well technology, Statoil explained.

All of the production wells at Troll oil are horizontal wells. This means drilling in two stages, initially down to the reservoir which is 1,600 metres below the seabed, and then up to 5,500 metres horizontally into the reservoir. Most of the wells are so-called branch wells, which mean that they have two or three horizontal sections that are gathered at a crossroad in the reservoir.

Norway’s largest producer

To date 200 wells have been drilled around Troll B and C, which combined have produced 1.56 billion barrels of oil. Troll oil has been Norway’s largest oil producer for the past three years.

“We still have great ambitions for production, and are stretching for 2.1 billion barrel mark in the field’s lifetime. The current recovery rate for oil is 40%, with a goal to reach 52%,” Norwegian oil and gas giant said.

The Troll oil adventure alone has generated an estimated NOK 460 billion in income, with investments so far of around NOK 100 billion.

The oil is transported to Mongstad, from Troll B through the Troll Oil Pipeline I (completed 1995; 16″ diameter, 85 km length, transport capacity 42,500 m3/day), and from Troll C through the Troll Pipeline II (completed 1999; 20″ diameter, 80 km length, transport capacity 40,000 m3/day). Associated gas goes to Troll A.

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