Diverless Installation of the Skuld Modular Subsea Station
- M. Freudenreich (Elf Aquitaine)
- Document ID
- Society of Petroleum Engineers
- SPE Drilling Engineering
- Publication Date
- June 1989
- Document Type
- Journal Paper
- 179 - 186
- 1989. Society of Petroleum Engineers
- 1.10.1 Drill string components and drilling tools (tubulars, jars, subs, stabilisers, reamers, etc), 4.2.4 Risers, 4.1.2 Separation and Treating, 1.10 Drilling Equipment, 1.6 Drilling Operations, 4.5.7 Controls and Umbilicals, 4.3.4 Scale, 4.1.4 Gas Processing, 4.1.5 Processing Equipment
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In 1984 and 1985, the Skuld experimental station was remotely operated and intensively tested in North Sea conditions for 1 year. This full-scale station, simulating production from a two-well cluster, was installed diverless in June 1984 outside Bergen, Norway, at 90-m [295-ft] water depth. Installation took less than 6 hours per module because we used guidelines and a dedicated landing tool, and the 1-year intensive test confirmed the reliability of the subsea equipment. This experiment demonstrates the validity of the development scheme using the Skuld modular concept.
The first offshore production installations were adapted from exciting onshore installations to meet the new environment. A permanent effort has been devoted to the optimization of offshore production equipment and structural supports to permit economical developments in deeper water. Today the oil industry faces another challenge that requires the development of new technologies-the water depth becomes so great that the use of permanent structural support is questionable with regard to feasibility and/or economic viability. In addition, diver assistance at such water depths is risky, limited, or even impossible. Therefore, underwater technology that considers diverless procedures must be developed,
For more than 20 years, Elf Aquitaine developed a research program for underwater technology. The first step of this program, program for underwater technology. The first step of this program, the North East Grondin pilot well, led to the decision to develop North East Frigg with underwater equipment, However, this development, which was successfully completed in Dec. 1983, includes a permanent surface support located in the vicinity of the subsea production station. This permanent surface support represents an important part of the investment cost and would render smaller fields or development in deep water economically nonviable. Therefore, we initiated a program for the design, development, and reliability assessment of an underwater technology suitable for the development o, deepwater fields on the Norwegian continental shelf. This research program was named Skuld for the major Viking divinity who symbolized future and necessity.
The first objective of Skuld was to investigate ways of developing an offshore satellite field a long distance from existing surface fa-cilities without using any permanent support in the vicinity and considering the North Sea environment. Consequently, two main goals became the basis of the Skuld program: (1) to improve equipment reliability (mainly control system) to minimize the operating cost and (2) to study the subsea equipment's ability to cope with the hostile conditions of the North Sea by using diverless procedures. Therefore, Skuld constitutes an important part of the initial research program by consolidating the results of the first step and by program by consolidating the results of the first step and by extending the validity of diverless techniques to deeper water and a harder environment.
Basic Development Scheme
Design. Table 1 presents basic field data for the Skuld development. A subsea template is used as a base to drill the wells and to support the manifold. The gas produced by four underwater Christmas trees (wet type) is collected by the manifold and flows through 5 x 20-cm [2 x 8-in.] -diameter sea lines to the permanent surface facilities, where all the equipment for gas treatment. metering, and com-pression is located.The subsea station is remotely operated and controlled from the distant surface facilities by means of a multiplexed, electrohydraulic control system located on the subsea station. This control system is linked to the emergency shutdown system of the surface facilities. Electrical power and coded messages are transmitted from the processing platform to the underwater control system by a subsea cable. processing platform to the underwater control system by a subsea cable. In a backup mode, the marking buoy is installed in the vicinity of the subsea station to provide the required navigational aid and is used as the radio relay for the signal transmission. Moreover, the electrical generator located on board supplies the power to the marking equipment and to the underwater control system. Figs. 1 and 2 show the field architecture and the basic flow diagram, respectively.
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