Enhanced Oil Recovery by Utilization of Multilateral Wells on the Troll West Field

Abstract

Abstract Norsk Hydro has been installing multilateral wells for 10 years. By the end of March 2006, a total of 64 multilateral junctions were installed. The vast majority have been sealed TAML level 5 junctions constructed from floating vessels, primarily on the Troll West field. Hydro identified early multilateral wells as a key technology to enhance the oil recovery from the Troll West field. In 1995, a multilateral technology vendor was selected as supplier of multilateral systems. The close cooperation between Hydro and the multilateral technology vendor has been the key to the development of new multilateral systems and system variants to meet new requirements for the implementation of this emerging technology. This paper will briefly describe the development of the FlexRiteÒ system and the subsequent variants like FlexRiteÒ Intelligent Completion Interface and ReFlexRiteÒ. Field operations involving these systems will be discussed, and the use of multilateral wells on Troll West will be presented in some detail with respect to; statistics for junctions installed by March 2006, presentation of example wells and economic effects from the use of multilateral wells. Introduction to the Troll West field The Troll Field is located approximately 80 km north west of Bergen, in the Norwegian Sector of the North Sea. The water depth is 315 - 340m. The field is divided by two major, curved, north-south trending faults which separate the field into three provinces. Troll West Oil Province (TWOP) and Troll West Gas Province (TWGP), both producing from a sandstone reservoir and operated by Norsk Hydro. The third province is Troll East with gas production, operated by Statoil. The Troll West oil column is approximately 22–26m thick in TWOP and 11–13m thick in TWGP. The overall area of the field is 200 sq.km. The combined development is estimated to recover a total of 1.45 billion barrels of oil. Norsk Hydro started production from the Troll B platform in 1995 and from the Troll C platform in 1999. Statoil started gas production from the Troll A platform at Troll East in 1996. There is communication between the three areas that affect the fluid flow and have impact on production strategy of the field. When the field was discovered back in 1979, and for many years to follow, it was considered a gas field with no commercial oil available. Today the Hydro operated part of the field is producing approximately 200 000 bbls/day of oil, making it the second largest producing oil field in the North Sea. The field currently accounts for more than 11% of Norway's oil production. The multilateral well concept was introduced on Troll West primarily to increase the total drainage area from the existing sub-sea template structures. New horizontal producers are continuously being drilled to recover reserves from the relatively thin oil layers before gas production induces oil column movements that are too large. By March 2006, a total of 109 wells had been drilled and completed on the Troll West Field, including 41 multilateral wells with a total of 54 multilateral junctions.