A Large Deck Extendable Draft Platform Design for Ultra-Deepwater in the Gulf of Mexico

A new delivery scheme based on an Extendable Draft Platform (EDP), designed for large fields in ultra-deepwater, offers potential benefits that minimize start-up costs and enhance overall economics. This paper describes an EDP design intended for deployment in water depth of 8,500 ft in a Gulf of Mexico environment. This deck design is one of the largest to date, using the EDP delivery method. The paper discusses design philosophy in detail, explaining the unique design features of the topsides for dockside commissioning, the deck connection system, and the riser systems and their integration. The topsides has process capacity of 200,000 bopd and about 475 mmcfd of gas. The deck also supports a drill rig with a hook capacity of 1,500 kips. The 40,000-ton topsides are 316 ft by 316 ft, supported by four 76-ft diameter columns. In addition to supporting the equipment, the topsides design supports 12,500 tons of riser tension. The complete process and drilling systems are assembled and commissioned dockside in less than 40 ft water depth. The entire system is floated on the deck barge, with the columns lowered through the deck and locked into position on site. Then the columns are de-ballasted, and the platform is raised to the operating draft. The top tensioned risers (TTRs) are supported by hydraulic tensioners. The mooring system, a major component of the lowering mechanism that deploys the EDP, comprises 12 lines composed of chain and polyester rope. These lines are pre-set and connected to the hull prior to raising the deck.