This paper reviews the planning, preparation and initial implementation of drilling operations for the latest phase of development of Phillips Petroleum's Ekofisk Field in the Norwegian Sector of the North Sea. This development includes the addition of 32 new production and injection wells to the existing t 80 well field. The unique aspect of the project was that, at the time of conception of the project, only 8 spare slots were available on existing structures, and preliminary economics proved the addition of a new structure unfavorable. The decision to utilize existing structures for the additional wells created many challenges for Phillips Petroleum Norway's engineers and this paper describes a number of the more interesting and unexpected of those challenges and their solutions.
The Ekofisk field is the largest of the Phillips Norway Group's seven field " Greater Ekofisk" operation, located in the south west corner of the Norwegian sector of the North Sea. An overview of the " Greater Ekofisk" infrastructure is shown in fig.1. The Ekofisk field itself now comprises three production and two injection platforms, as well as eight other accommodation, process and transportation facility platforms.
Production from the Ekofisk field peaked in 1980 with production figures of 618rO00 BOPD and 1,860 NMSCFD of gas. production decline, led to the evaluation and pilot study of a field water injection program. In 1986, the Ekofisk field water injection program commenced from the 2/4 Kilo injection platform (30 well slots capacity). Water injection into the Ekofisk reservoir reached 375rO00 BWPD in 1990 into a total of 20 wells.
Positive results prompted Phillips to evaluate further development of water injection coverage, as well as adding producers to optimize recovery from the reservoir. The location of 2/4 Kilo, near the north end of the Ekofisk field, limits access to the center and south end of the field for injection purposes. Also, in 1986r nearly all 56 well slots located on the three Ekofisk production platforms, 2/4 Alpha (16 slots), 2/4 Bravo (24 slots) and 2/4 Charlie (16 slots) had been utilized. As a result, studies were initiated to evaluate the options for increasing the number of well slots at different locations in the field. Various scenarios were considered including new wellhead platforms, cantilever extensions to existing structures, and modifications to existing facilities. The decision was finally made a) to modify two of the existing production platforms (2/4 Alpha in the South of the field, and 2/4 Charlie near the field center) to add eight extra well slots on each structure, and b) to modify one of the bridge support tripods at the south end of the Ekofisk complex to accept a wellhead module for eight water injection wells. The location of the bridge support was ideal, in that it gave access to center and southern areas of the field for improved water injection coverage. The new injection platform was assigned the designation - 2/4 W.