This paper describes the experience and learning gained whilst, designing, planning and installing a Multi-Lateral Well on the Forties field operated by BP Exploration in the UKCS. This project was initiated by the Research and Development groups of BP Exploration and Halliburton Energy Services, and sponsored by the European Union's Joule-THERMIE Program which supports the implementation of technology in Europe. The objectives of the project were to drill and complete a dual lateral well with commingled production, at minimum risk and cost, and to monitor and report the production performance. The difference between this project and the majority of multi-lateral wells drilled to date will be the installation of a cemented junction with connectivity, isolation and re-entry capability. The successful execution of this project will provide the industry with data on the long term performance of a cased hole, cemented, junction design. It will also provide production performance from a dual lateral well and give details of the challenges facing the management of such a well in a mature field environment. It is anticipated that this will lead to increases in the application of this technology, improve the economical recoverable reserves from mature fields and reduce the cost of new fields.
Multi-lateral wells offer innovative and economical ways to produce hydrocarbons. Economic analysis on Forties shows that for in-fill drilling, the cost to drill and complete a dual lateral well is less than the cost to re-drill two wells and becomes particularly attractive on platforms where the number of available well slots is limited. However, until recently, the application of multi-lateral wells was limited to wells that did not require through tubing reservoir access for stimulation or water, scale and sand management.
Junction construction advances through system development and testing by Longbottom demonstrated the possibility existed of cost effectively constructing and installing a design which provided isolation, access and connectivity. The experience and learning gained by the implementation of this project, enhances the ability to construct a cased and cemented dual lateral, operate each lateral as a separate well and perform those remedial operations presently available to the industry.
The risk and uncertainty surrounding a project of this nature means that without the support of programmes like THERMIE, initial economics are sensitive when it comes to applying new technology in a mature field environment such as Forties. Remaining well targets are relatively small and production is complicated by demands for sand, scale and water management. In-fill and sidetrack drilling is expected to continue at least until 1999. If the recent success of the in-fill program continues, some platforms will become slot constrained. The application of new technologies, like multilateral wells, are expected to enable more targets to be reached from fewer surface locations. This well is the first step in this new direction.
The Forties field (Fig. 1) was the first major oil field discovered in the British sector of the North Sea. The field is located predominantly in block 21/10 and lies some 180 km (112 miles) ENE of Aberdeen. The discovery well drilled in 1970 encountered oil in good quality Paleocene sands. Further appraisal drilling confirmed a Stock Tank Oil Initially in Place of approximately 4.2 billion barrels. The field was developed as described by Brand et al using 5 platforms (Alpha, Bravo, Charlie, Delta and Echo) with first oil being produced in 1975. To date, 2.2 billion barrels have been produced. It is estimated that a further 280 million barrels of oil will be recovered from the field. P. 227
