Design, Fabrication, Hookup, and Commissioning of North Cormorant Topside Facilities

Abstract

Summary The North Cormorant platform in the North Sea was built and commissioned within budget and ahead of schedule to a high standard of quality. Some of the factors relating to the topside facilities that helped achieve this successful result are described for each of the design, procurement, fabrication, hookup, and commissioning phases. Of key importance was careful attention to the project objective and to planning, control, organization, people, and contracting methods. Some recommended improvements for a future project also are addressed. Introduction The Shell/Esso North Cormorant platform went into production in Feb. 1982, less than 3 years after fabrication production in Feb. 1982, less than 3 years after fabrication started and 9 months after the platform jacket was launched (see Table 1). During this process, several new records and "firsts" for the North Sea oil industry were set, but most important perhaps were the records of cost containment and schedule achievement without any sacrifice in quality of the finished product. It is believed that new standards of efficiency and economy have been attained. The piled steel platform accommodates a combined drilling and production operation. Provision is made for 40 well slots and a number of J-tubes to permit subsea production/injection development should it be required production/injection development should it be required later. The facilities are designed to process a crude throughput of 180,000 B/D [28 600 m3/d] and a water treatment and injection rate of 220,000 B/D [35 000 m 3 /d]. Crude oil is exported at 90 psi [621 kPa] through a 20-in. [5 1 -cm] pipeline to Cormorant A and thence into the Brent System pipeline; a 10-in. [25-cm] pipeline ties the platform to the western leg of the Far Liquids and Associated Gas System (FLAGS) for export of sales gas. Accommodation is provided in a living quarters block with 124 cabins to give maximum bed occupancy of 240 men, and the quarters are surmounted by a landing pad designed for Chinook helicopters. The operating weight of all topside facilities is 17,000 U.K. tons [864 Mg] which includes 5,500 U.K. tons [279 Mg] for the single drilling rig with maximum derrick pull and a full complement of consumables. This operating weight is substantially lower than achieved to date elsewhere in the North Sea for comparable platform capabilities. This paper describes methods adopted to contain costs and meet schedules in the interests of the project objective, which was to maximize the economic return from the development with due consideration for proper reservoir management, safety, and quality standards. The paper specifically addresses the topside facilities, and it complements two other papers one reviewing the project as a whole and the other addressing the platform substructure. The work phases are covered from development of the design concept through offshore hookup and commissioning. Several new approaches were adopted in the course of executing the project, and these are explained where there is potential application for future projects. Inevitably, improvements could have been made to achieve even better results, and some of these also are explained. Design Concept The chosen method of development of the North Cormorant field was installation of a single fixed platform located centrally in the field and supported at a later date, if necessary, by subsea wells to tap the extremities of the reservoir beyond the reach of platform wells. The first phase was to establish the design concept for the topside phase was to establish the design concept for the topside facilities on which to carry out the detailed design and engineering. The dominant considerations in establishing the design concept were, as for all phases of project execution, cost, schedule, and quality. Therefore, particular emphasis was given to separating the true needs for an operable and safe facility from the desirables, which are not strictly necessary. Appraisals were based on economic return and denied if there would be no positive contribution. Operational flexibility and facility maintenance were key considerations, for the former can affect production uptime and the latter maintenance costs and, at worst, production uptime, too. Efficiency and speed of offshore hookup production uptime, too. Efficiency and speed of offshore hookup and commissioning were addressed carefully, since these greatly influence both project costs and the schedule to first production, and were recognized as an area where the greatest gains might be made. In addition, for each tonne of facilities installed there is a requirement for roughly the same weight of structural steel in modules, and both weight and space have a profound effect on the substructure. For operational flexibility, two process trains of three-phase separation (each with two stages) and of gas compression to export pipeline pressure were selected. JPT P. 124