Troll

11.04.2012
   

The Troll field lies in the northern part of the North Sea, about 65 kilometres west of Kollsnes. The water depth in the area is more than 300 metres. The field has huge gas resources and one of the largest oil volumes remaining on the Norwegian continental shelf. Troll has two main structures: Troll Øst and Troll Vest. About two-thirds of the recoverable gas reserves lie in Troll Øst. A thin oil zone underlies the gas throughout the Troll field, but so far only in Troll Vest is this oil zone of sufficient thickness to be commercial, 11 - 27 metres. In 2007, an oil column of 6 - 9 metres was proven in the northern part of Troll Øst. A test production of oil from this part of Troll started in November 2008. A phased development has been pursued, with Phase I recovering gas reserves in Troll Øst and Phase II focused on the oil reserves in Troll Vest. The gas reserves in Troll Vest will be developed in a future phase III. The Troll licensees are conducting studies to plan for further development of the field.

 

Troll I

Troll I 


Blocks and production licences

  • Block 31/2 - production licence 054, awarded 1979
  • Block 31/3 - production licence 085, awarded 1983
  • Block 31/3 - production licence 085 C, awarded 2002
  • Block 31/3 - production licence 085 D, awarded 2006
  • Block 31/5 - production licence 085, awarded 1983
  • Block 31/6 - production licence 085, awarded 1983
  • Block 31/6 - production licence 085 C, awarded 2002

Development approval 15.12.1986 by the Storting

Discovered 1983

On stream 09.02.1996

Operator Statoil Petroleum AS

Licensees

  • A/S Norske Shell 8.10 %
  • ConocoPhillips Skandinavia AS 1.62 %
  • Petoro AS 56.00 %
  • Statoil Petroleum AS 30.58 %
  • Total E&P Norge AS 3.69 %

Recoverable reserves

Original - Remaining as of 31.12.2011

  • 1410.9 billion Sm³ gas - 1019.1 billion Sm³ gas
  • 27.7 million tonnes NGL - 22.2 million tonnes NGL
  • 1.6 million Sm³ condensate -

Estimated production in 2012

  • Gas: 31.03 billion Sm³
  • NGL: 1.08 million tonnes

Expected investment from 2011 28.4 billion 2011 values

Total investment as of 31.12.2010 45.3 billion nominal values

Main supply base Ågotnes

 

Development:
Troll Phase I has been developed with Troll A which is a fixed wellhead and compression facility with a concrete substructure. Troll A is powered by electricity supplied from land. An updated development plan involving the transfer of gas processing to Kollsnes was approved in 1990. Kollsnes was separated from the unitised Troll field in 2004, and the Kollsnes terminal is currently operated by Gassco as part of the Gassled joint venture. The gas compression capacity at Troll A was increased in 2004/2005. The Troll Oseberg Gas Injection (TOGI) subsea template is also located at Troll Øst. Gas was exported from this template to Oseberg for injection. The TOGI decommissioning plan involving removal of the subsea template was approved in 2005.

Reservoir:
The gas and oil reservoirs in the Troll Øst and Troll Vest structures consist primarily of shallow marine sandstones belonging to the Sognefjord Formation of Late Jurassic age. Part of the reservoir is also in the Fensfjord Formation below the Sognefjord Formation. The field consists of three relatively large rotated fault blocks. The fault block to the east constitutes Troll Øst. The reservoir depth at Troll Øst is about 1 330 metres. Pressure communication between Troll Øst and Troll Vest has been proven. Previously, 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.

Recovery strategy:
The gas in Troll Øst is recovered by pressure depletion through 39 wells drilled from Troll A.

Transport:
The gas from Troll Øst and Troll Vest is transported through three multi-phase pipelines to the gas processing plant at Kollsnes. The condensate is separated from the gas, and transported by pipeline partly to the Sture terminal, and partly to Mongstad. The dry gas is transported in Zeepipe II A and II B.

Status:
Installation of two more gas compressors is ongoing on Troll A. The TOGI decommissioning will be completed during 2012.


 

Troll II

Troll II

 

Blocks and production licences

  • B Block 31/2 - production licence 054, awarded 1979
  • Block 31/3 - production licence 085, awarded 1983
  • Block 31/3 - production licence 085 C, awarded 2002
  • Block 31/3 - production licence 085 D, awarded 2006
  • Block 31/5 - production licence 085, awarded 1983
  • Block 31/6 - production licence 085, awarded 1983
  • Block 31/6 - production licence 085 C, awarded 2002

Development approval 18.05.1992 by the Storting

Discovered 1979

On stream 19.09.1995

Operator Statoil Petroleum AS

Licensees

  • A/S Norske Shell 8.10 %
  • ConocoPhillips Skandinavia AS 1.62 %
  • Petoro AS 56.00 %
  • Statoil Petroleum AS 30.58 %
  • Total E&P Norge AS 3.69 %

Recoverable reserves

Original - Remaining as of 31.12.2011

  • 255.8 million Sm³ oil - 35.1 million Sm³ oil

Estimated production in 2012

  • Oil: 122 000 barrels/day

Expected investment from 2011 27.1 billion 2011 values

Total investment as of 31.12.2010 76.7 billion nominal values

Main supply base Mongstad

 

Development:
Troll Phase II has been developed with Troll B, a floating concrete accommodation and production facility, and Troll C, which is a semisubmersible accommodation and production facility made of steel. The oil in Troll Vest is produced by means of several subsea templates tied back to Troll B and Troll C by flowlines. Troll Pilot, which was installed in 2000 at a depth of 340 metres, is a subsea facility for separation and re-injection of produced water. The Troll C facility is also utilised for production from the Fram field. The Troll C development was approved in 1997. There have been several PDO approvals in connection with various subsea templates at Troll Vest.

Reservoir:
The gas and oil in the Troll Øst and Troll Vest structures are found primarily in the Sognefjord Formation which consists of shallow marine sandstones of Late Jurassic age. Part of the reservoir is also in the underlying Fensfjord Formation. The field comprises three relatively large rotated fault blocks. The oil in the Troll Vest oil province is encountered in a 22–26 metre thick oil column under a small gas cap, located at 1 360 metres depth. The Troll Vest gas province has an oil column of about 12-14 metres under a gas column up to 200 metres in thickness. A significant volume of residual oil is encountered immediately below the Troll Vest oil column. There is a minor oil discovery in the Middle Jurassic Brent Group, below the main oil reservoir.

Recovery strategy:
The oil in Troll Vest is produced by means of long horizontal wells which penetrate the thin oil zone immediately 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. Several multi-branch wells have been drilled, with up to seven branches in the same well. In the Troll Vest oil province, some of the produced gas is re-injected into the reservoir to optimise oil production.

Transport:
The gas from Troll Øst and Troll Vest is transported through three multi-phase pipelines to the gas processing plant at Kollsnes. Condensate is separated from the gas and transported onwards by pipelines, partly to the Sture terminal, partly to Mongstad. The dry gas is transported through Zeepipe II A and Zeepipe II B. 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:
Drilling on Troll Vest with horizontal production wells from subsea templates continues. There are presently about 120 active oil production wells at Troll Vest. Over the last few years, decisions have been continuously made to drill new production wells to increase the oil reserves in Troll. A four-rig drilling strategy has been implemented.

 

Troll

The graph shows total production from Troll l and Troll ll. 

 

Troll II