Elegant and sleek, Kerr-McGee's newest spar design has chalked up several "firsts" and promises to be a highly-efficient, economical deepwater production solution.

Sometime this summer, Kerr-McGee and Devon will launch Red Hawk, a revolutionary new spar design to ultimately produce 300 MMcf/d of gas from 5,300 ft (1,615 m) of water in Garden Banks 877 in the Gulf Of Mexico. In keeping with Kerr-McGee's fast track approach, the company expects to see first oil less than 3 years after discovery. A 76-mile (122 km), 18-in. pipeline will link Red Hawk, first to the company's Vermilion 397 platform, and then by 24-in. pipeline to the Patterson Gas Plant.

Red Hawk is the brain child of veteran spar pioneer Ed Horton, whose designs have been used for several of Kerr-McGee's spars. The company has rapidly progressed from classic spar designs, such as Neptune, through several truss designs, notably Nansen, Boomvang and Gunnison, to the cell design. With the majority of spars presently operating in the Gulf of Mexico, Kerr-McGee has developed a world of experience that allows them to improve on design features as well as operating techniques that pay off at the bottomline with greatly reduced costs.

The first thing you notice when you tour the Red Hawk construction site at Technip's Ingleside yard is the spar's unusual profile. Slim and svelte, the spar consists of a bundle of six tubes equally-spaced around a seventh, core tube. Each tube is 20 ft (6 m) in diameter and has been constructed by welding cylindrical cells end-to-end to form chambered tanks. The center tube and three of the outer tubes are 280 ft (6 -m) long. They form part of the "hard tank" that provides buoyancy and fluid storage. The other three outer tubes are 560 ft (170 m) long. The upper ends of these long members are also part of the hard tank and the lower ends comprise the "soft tank" that contains the magnetite ballast. Four large horizontal plates equally-spaced along the lower hull tie the long tubes together while providing heave dampening, and external strakes suppress vortex-induced vibration (VIV) from ocean currents. In all, the hull's diameter is only 64 ft (19 m).

In building Red Hawk, Kerr-McGee recorded several firsts. Besides being the first application of cell spar technology in the world, the spar is the first built entirely in the United States. Previously, spar hulls were fabricated in Europe and transported to the Gulf using submersible heavy-deck cargo carriers. Red Hawk will also be the first spar moored using lightweight polyester lines. The 8.5-in. diameter braided polyester ropes are rated at 2,800 kips, comparable to 5-in. diameter steel cable, but enjoy a 7:1 weight advantage. Tension will be maintained by varying the buoyancy of the hard tank by pumping-in or bleeding-off air, eliminating the need for an elaborate system of tensioning winches. Individual mooring line tensioning and control is accomplished using a single windlass that is shared by all six mooring lines. Because this is the first use of polyester mooring lines in mooring deepwater production spars, the company has installed 45-ft (13-m) test inserts that will be routinely retrieved, tested and replaced every 3 months. Any deterioration will be detected long before it becomes critical. A modular glycol reclamation unit will be used for hydrate inhibition and gas dehydration. It will treat and recycle the glycol with an expected efficiency of more than 95%.

Red Hawk's topsides are also being fabricated at Technip's Ingleside yard. The three-deck topsides module will be mated to the top of the spar in a single lift on location using a heavy-lift semisubmersible crane. The fully automated topsides is designed for efficient operation using a crew of six on 7-day rotation - an offshore installation manager, two operators and three technicians.

With Red Hawk, Kerr-McGee is breaking new ground is spar design. The cell spar is (relatively) easy to build and maintain, and elegant in its simplicity. Economical to build, operate and maintain, it is expected to optimize profitability for the company in applications where the cell spar design makes sense.




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