The Truss Spar is a new floating platform concept that is rapidly becoming one of the preferred systems for developing deepwater Gulf of Mexico fields. The Truss Spar provides a stable, cost-effective platform for dry-tree completions over a wide range of water depths. The Truss Spar is an extension of technology developed on previous "Classic" Spar projects, but has several specific advantages. These advantages were exploited to provide a fit-for-purpose platform solution for the Nansen/Boomvang Field Development. This paper describes the design of the Truss Spars for the Nansen/Boomvang Field Development. The paper reviews the Truss Spar concept, past development work, and comparison with the Classic Spar concept. The paper describes the specific Nansen/Boomvang project requirements and design criteria and how they influenced the platform configuration. The paper includes summaries of analysis results for global motions, mooring design, and hull structural design. The paper also includes a description of unique design features, including heave plates, SCR pulltubes, hard tank-to-truss connections, and toptensioned riser guides. These novel features, and other technology proven on the Nansen/Boomvang project, are readily transferable to other Truss Spars now under design.
This paper describes the fabrication and installation of the offshore facilities for the Nansen and Boomvang projects. The paper will review the benefits realized from building and installing two nearly identical facilities on an aggressive project schedule. We will describe the fabrication of the hulls at Mäntyluoto Works in Pori, Finland and the decks at J. Ray McDermott in Morgan City, Louisiana. The offshore program will be detailed from the mooring pile installation through the uprighting of the hulls and setting of the topsides. The team solutions to challenges associated with the coordination of fabrication and installation activities and schedules will be described.
Th(s paper was prepared for presentation at the Offshore Technol~Con feren&s held m Houstm, Texas 6-9 May 19% Thm pawr was Wetted for presentabon by the OTC Program Ccmmttee follmwng revww of (nforma(mn wnlamed In an abstract submltled by the autfmrs Contents of Ihm paper as presented have not been revwwed by the Offshore Technology Conference and are subpcf lo correctmn by the authors Tlw material, as presented, dms not rmcesserdy reflect any posmon of the Offshore Techrmlcqy Conferenc9 of 11sDfiicers Pemnlss!On to copy IS IImlted 10 an abstract of not mwe than 300 words Illustrations may not be cnpmd The abstrw should Wntatn COnsplcucus acknowledgment of where and by whom the paper .+ms presented AbstractOffshore platforms with integrated, lift installed decks have become increasingly common design concepts in the last ten years based on the availability of super heavy lift crane vessels in certain parts of the world. High installation costs for these lifting vessels have led operators to investigate alternate installation methods. The integrated, float-over ("IFO') deck concept has been utilized several times in the last I 7 years. Recent successful design and installation experiences with integrated, float-over decks in the Far East have encouraged operators and designers to consider this concept more frequently for applications in other areas. The purpose of this paper is to describe some of these recent experiences and how the experience might be applied for similar offshore developments in the future. Design and installation considerations are reviewed and recommendations made for future applications of the concept.The concept consists of a steel topsides deck structure which is conventionally loaded out onto a floating transportation barge. After transportation to the offshore location, the barge is maneuvered ("docked") inside the legs of a platform substructure and installed ("mated") by lowering down the transportation vessel. Depending on the weight of the integrated deck and the directionality and magnitude of prevailing environmental conditions, a passive, partially active, or fully active mating system is utilized for the load transfer operation. The separate benefits of the integrated deck concept and the float-over deck concept make this an attractive combined concept worthy of application for different sizes and weights of topsides and varied offshore locations, The benefits for design, fabrication, installation, hookup/commissioning, operations, and schedule are summarized for the integrated, float-over deck concept compared with modular, lift installed decks. The paper discusses the development of various details for particular applications. The development of a platform structural configuration based on the weight of the topsides, transportation vessel selection, and required size of vessel opening in the structure are discussed. Installation equipment including vessel systems (fendering, mooring, and rapid ballasting) and load transfer systems (structure fendering, alignment, guides, and pas...
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