The Terra Nova FPSO Turret Mooring System

Abstract

Abstract The Terra Nova FPSO consists of a new-build vessel with a disconnectable internal turret mooring system. Nineteen risers and umbilicals from four drill centers are connected to the turret with a maximum design throughput of 150,000 bopd. The turret system is designed to allow the vessel to quickly disconnect from its moorings and risers to avoid impact with unacceptably large icebergs, and to allow the FPSO to remain moored on station during the severe 100-year storm conditions. These unique requirements for Terra Nova have resulted in the development of one of the most sophisticated turret mooring systems to date. This paper presents some of the key drivers that led to the unique design of the Terra Nova turret mooring system, and provides a detailed description of the various components of the turret, focusing on both the structural and mechanical, and the fluid-transfer systems. The paper also provides an overview of the disconnection and reconnection of the turret mooring system, illustrating its compliance with the stringent requirements in the design basis. Finally the paper provides a summary of the turret design, fabrication and installation milestones over the life of the project. Introduction The Terra Nova FPSO will be located in approximately 95 meters water depth on the Grand Banks off the East Coast of Newfoundland, Canada. The harsh environment at the Terra Nova location is much like the northern North Sea with a 100- year significant wave height of 16 meters, and 1-hour mean wind speeds of 40 m/s. The FPSO is situated in "iceberg alley" where large icebergs from Greenland and Ellesmore Island drift south with the Labrador current. Surveys have shown the presence of iceberg scour marks on the seabed, and statistics indicate that the site could see as many as 66 large icebergs in a single season (April - July). Table 1 provides a summary of the design storm conditions for both the 1-year and 100-year return intervals. The Terra Nova FPSO system consists of a new-build FPSO vessel with a disconnectable internal turret mooring system. The turret supports 14 risers and 5 umbilicals servicing wellheads in four or more glory holes, with a maximum design throughput of 150,000 bopd. The turret mooring system has been designed to maintain station in the 100-year storm environment, and to be disconnectable to avoid an approaching iceberg on a collision course. Once the FPSO disconnects, the mooring and riser system is supported by the spider buoy that has an equilibrium depth of 35 meters below sea level. This paper provides a detailed description of the unique turret mooring system designed by FMC SOFEC Floating Systems for the Terra Nova FPSO, focusing on both the structural and mechanical system, and the fluid-transfer system. The paper also provides a description of the disconnection and reconnection of the turret mooring system, and the design, fabrication and installation milestones over the life of the project.