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Development of an Oil Production Platform for Year-Round Operation in the Beaufort Sea
Norwegian University of Science and Technology, Faculty of Engineering Science and Technology, Department of Marine Technology.
2012 (English)MasteroppgaveStudent thesis
Abstract [en]

Due to high expectancy of hydrocarbon resources in the Beaufort Sea it is seen as an important area for energy in the future. As the focus now is shifting towards the deeper parts of the sea, there is a need for floating production platforms that are able to operate year-round in the harsh con- ditions of the Beaufort Sea. In this Master’s thesis the design of such a platform is performed, with respect to global ice loads acting on the plat- form and the capacity of the stationkeeping system. This is used to analyse the operability of the platform. To be able to develop a floating production platform it is crucial to have information on ice conditions in the Beaufort Sea. Literature has been used to determine ice conditions in the seasonal transitional zone, where it is expected that the platform will operate. Factors such as level ice, first- year and multi-year ridge dimensions, floe size and ice island mass have been defined. These define some of the most common ice conditions in the Beaufort Sea, and as such represent ice conditions a platform can expect to meet. Functional specifications have been used to determine the most appropriate platform type. Several platform types were considered based on factors such as production and storage, ice loads, and ice interaction with risers and mooring lines. A circular FPSO was selected due to its insensitivity to ice drift direction. To reduce ice loading, the platform was designed as a downward sloping cone. Ice loads on the platform have been calculated using several methods com- monly applied in literature. Results show that managed ice yields lowest loads, followed by level ice. Higher loads are seen for ridges, both first-year and multi-year, and large ice floes. A water depth of 500 m was assumed for the location of the platform. Since this can be considered as a moderate water depth, a conventional mooring system was selected for stationkeeping. The system has 24 mooring lines connected to a buoy, which again connects to the turret on the platform. Internal mooring was seen as necessary to protect mooring lines from ice. Restoring coefficients have been determined using the inelastic catenary equations. Maximum allowable horizontal displacement is defined as 5 % of the water depth. This is used to determine the maximum allowable horizontal load on the platform to be 53.38 MN. Lastly, the operability of the platform was judged by comparing various ice loads to the maximum allowable load given by the mooring system. Ice management is clearly needed when operating in any ice other than level ice. The requirements of the ice management system has been defined, and a general analysis of the primary and secondary objectives of the ice man- agement system has been performed. It is proposed to use one icebreaker throughout the year, since the platform may encounter multi-year ice floes during the summer. As the ice season starts an additional ice breaker is introduced. In severe ice conditions it may be necessary with a third ice breaker. It is concluded that if proper ice management is ensured, the plat- form should be able to operate year-round.

Place, publisher, year, edition, pages
Institutt for marin teknikk , 2012. , 149 p.
Keyword [no]
ntnudaim:7194, MTMART Marin teknikk, Marin hydrodynamikk
URN: urn:nbn:no:ntnu:diva-18495Local ID: ntnudaim:7194OAI: diva2:565981
Available from: 2012-11-08 Created: 2012-11-08

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