Field Development Optimization using Linear Programming coupled with Reservoir Simulation - Ekofisk Field
Authors: Nesvold R.L. , Herring T.R. , Currie J.C. 
Published: December 2007

Abstract
The Ekofisk Field in the Norwegian North Sea is currently being redeveloped with the installation of a new processing platform and a new 50 slot wellhead platform. The new processing facilities are scheduled to be installed in 1998 and will serve as a central processing point for the Ekofisk field and all of the outlying fields in the Greater Ekofisk Area. Drilling operations on the new well head platform will commence in 1996 and will result in the drilling of up to 50 wells over the next eight years. In order to maximize the value of this major redevelopment, a project was initiated to optimize the development strategy for Ekofisk and the outlying fields. This paper describes the tools developed during this project. Two different techniques of coupling linear programming and reservoir simulation were developed independently using iterative approaches to obtain solutions. The results of the two approaches yielded very similar solutions, which provides a high degree of confidence in the solution techniques.

Introduction
The redevelopment of the Ekofisk field, also known as the Ekofisk II project, has a significant impact on both Ekofisk and the outlying fields in the Greater Ekofisk Area. The new 2/4 J Processing Platform will be installed in 1998 and will consolidate all Greater Ekofisk Area Oil and Gas processing on one platform. The new processing platform will accommodate production from the Ekofisk Eldfisk, Embla and Tor fields, as well as any future developments. The new 50 slot 2/4 X Wellhead Platform will be installed in 1996 and used to redevelop the Ekofisk Field, eventually replacing the existing 2/4 Alpha and 2/4 Bravo Platforms.
Early in the stages of the Ekofisk II project, it was decided to design the new processing facilities to plateau production for the first few years. While plateauing production generally provides the most attractive economic alternative, it significantly complicates the development planning for a field. In the case of the Ekofisk II project, a large number of economically viable opportunities existed to increase production and a procedure was required to optimize scheduling of these projects. Table 1 summarizes the number of projects that were under consideration.
The rate at which these projects could be developed was governed by two major constraints: processing capacity and rig availability. The new Ekofisk II processing facilities limited gas processing to 789 MMSCFD and oil to 274 MBOPD.
Drilling constraints varied by platform. Fixed platform rigs capable of drilling six wells per year existed on Ekofisk X and Eldfisk Bravo platforms. One jackup rig was also available, and was capable of drilling six well per year on Ekofisk X, Eldfisk Alpha, or Tor Platforms. The jackup was also capable of drilling on Embla, but was limited to four wells per year due to the longer drilling times for the deeper, higher pressured Embla reservoir. No drilling was premised on Ekofisk Alpha, Ekofisk Bravo or Ekofisk Charlie platforms. Table 2 summarizes the drilling constraints for the Ekofisk II project.
Within these constraints, a number of different development strategies were possible. Four of the most significant options that required evaluation were as follows:Accelerating drilling on outlying fields. Excess processing capacity existed prior to start up of the new process facilities in 1998. Opportunities existed to increase production on the smaller outlying fields prior to 1998, but the long term production impact of these projects would reduce the processing capacity available after start up of the new facilities. The value of this accelerated production had to be weighed against the potential impact of delaying higher value Ekofisk X Platform wells until after the plateau period.
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