Ekofisk Area Reservoir Management and Redevelopment
Authors: Landa G.H. , Holm W.H. , Hough E.V. 
Published: October 2008

Abstract
The Ekofisk Area consists of 8 fields located in the Norwegian Sector of the North Sea. This includes three gas condensate fields (Cod West Ekofisk and Albuskjell) and five volatile oil fields (Edda, Ekofisk Eldfisk, Embla and Tor). The Ekofisk field was discovered in 1969 and was the first major oil field discovered and developed in the Norwegian North Sea. This paper describes the development of the area with emphasis on the Ekofisk field and the challenges and process that lead to the redevelopment of the field (Ekofisk II). Reservoir management has enabled a significant increase in production and reserves above the initial estimate. The redevelopment with the installation of a new 50 slot wellhead platform and a new processing platform has created new opportunities as well as new constraints. The process of optimizing the value of the assets is described. The paper also describes subsidence and its impact on production strategy and facilities design criteria. Finally. the paper describes future opportunities with respect to EOR and reserves optimization of other fields in the area.

Introduction
The Ekofisk Area fields (Production License PI018) comprise eight fields in the southern part of the Norwegian Sector of the North Sea, Fig. 1. They include three gas condensate fields (Cod. West Ekofisk and Albuskjell) and five volatile oil fields (EDDA. Ekofisk, Eldfisk. Embla and Tor). The Ekofisk field was discovered in 1969 and was the first major oil field discovered and developed in the Norwegian North Sea. The Ekofisk Area fields produce from chalk formations of Danian and Maastrichtian age which are named Ekofisk and Tor formations respectively. The exceptions are the Cod and Embla fields which are sandstone reservoirs, the Cod reservoir of Paleocene age and the Embla reservoir of Jurassic age. Gas is transported from the Ekofisk Center to Emden. Germany. through a 441 km 36" pipeline while crude oil nd NGL is transported from the Ekofisk Center to Teesside, England, through a 354 km 34" pipeline. The Ekofisk Field Transportation and Processing Complex is a central hub for the southern portion of the North Sea. currently transporting hydrocarbons from Valhall, Hod. rna. Gyda, Tommeliten and Statpipe in addition to the production from the Greater Ekofisk Area. Due to high operating costs caused by aging facilities and subsidence it was decided in 1993 to redevelop the Ekofisk Area. This involved building one new processing platform (2/4 J) and one new wellhead platform (2/4 X) both to be installed at the Ekofisk field, Fig. 2. Four of the outlying fields within Production License PL 018 are premised to be shut-in prior to start up of Ekofisk II. These fields are Albuskjell, Cod, Edda and West Ekofisk. When the Ekofisk II APE was written the overall value identified for these fields were projected to be less than the cost of pipeline re-routing and tie-in to the new Ekofisk facilities.

Redevelopment Considerations

Reserves Management.
The Ekofisk Area has undergone a staged development since the Ekofisk field came on production in 1971. This includes development of the Ekofisk field itself as well as tie in of other fields in the area. The last field to be tied in was Embla in 1993.