Accumulated oil production from the Troll field offshore Norway will reach one billion barrels of oil in the spring of 2005. At 315-340 meters water depth, Troll is an oil and gas field with approximately 1,700 billions Sm3 of gas and four billion barrels of oil in place. Troll consists of two main structures, Troll East and Troll West, the latter divided into an oil and gas province. The oil is located primarily in Troll West in thin oil layers of 4-27 m. This article describes how the Troll West field has been developed from a gas field with no commercial oil to a gas and oil field with accumulated production surpassing one billion barrels of oil during the spring 2005.
This article describes the multi-disciplinary success story of the Troll West oil and gas field. Originally, the Troll field's thin oil layer of 4-27 m thickness was considered to have no commercial value. The development of horizontal drilling technology combined with early testing and oil production from a floating platform (FPSO) led to the conclusion that Troll West oil could be commercially produced. The most productive part of the field is the Troll West Oil Province (TWOP) with 22–27 m oil thickness. It was first developed by the installation of five subsea clusters and the Troll B FPSO in 1995. Drilling and production performance led to further development of the even thinner oil layers (4–14 m) in the Troll West Gas Province (TWGP), and installation of the separate Troll C platform, which began producing in 1999. The Troll field is one of the largest subsea developments in the world with 107 wells currently in operation. Increased oil recovery from the thin oil layers in Troll West has been possible by gradually increasing the length of the horizontal sections and introducing multi-lateral wells to reduce cost and increase the sweep area. Advanced drilling and completion technology have been developed and implemented. Seismic and geological methods determine the location of the high-permeable sands with high accuracy. The drilling and completion operations have been significantly more efficient, resulting in a higher drainage area per invested capital. Continous production drilling with up to four floating drilling rigs has been carried out since production start in 1995. More than 30 multi-branched wells with zonal control are in operation. Five three-branched, two four-branched and one five-branched well are currently in production.
Figure 1. The Troll Field is located some 80 kms west of Bergen, Norway. (available in full paper)
The Troll field is located some 80 kilometers west of Bergen, off the coast of western Norway. The water depth is 315-340 m. The Troll field consists of Troll East, mainly covered by production license 085, and Troll West, mainly covered by production license 054, see Fig. 1. The Troll license partners are:
ConocoPhillips Norge 1.62374 %
Total E&P Norge AS 3.69096 %
A/S Norske Shell 8.10145 %
Norsk Hydro Produksjon AS 9.77914 %
Statoil ASA 20.80471 %
Petoro AS (Norwegian state) 56.00000 %