Offshore: ABS to Class Cell Spar for Kerr-McGee

ABS is classing the industry's first cell spar destined for Kerr-McGee's Red Hawk field in deepwater Gulf of Mexico. The project marks ABS' fifth classification contract from Kerr-McGee Oil & Gas for a spar offshore facility. The project will draw on ABS' experience with spar technology and industry expertise for deepwater developments, says Luiz Feijo, ABS project manager.

"ABS offers Kerr-McGee the expertise to face the technical challenges of the Red Hawk frontier project while meeting the schedule requirements," said Feijo.

The entire project, adds Feijo, is expected to complete within two years of project sanction, with first-gas scheduled for second quarter 2004.

"Engineering and fabrication are proceeding in parallel. For ABS, this means we are working very diligently to review and approve designs in an efficient manner, without risk of delay," said Feijo.

He adds that ABS' experience in working with Kerr-McGee and its deepwater pursuits will help facilitate its participation in the effort. To date, ABS has supported Kerr-McGee with classification services for the caisson or classic first-generation spar and for the truss spar, a second-generation design using less steel while allowing additional deck load. ABS has classed the following Kerr-McGee spars, all installed in the Gulf of Mexico: the Neptune spar-a classic design; and the Nansen, Boomvang and Gunnison truss spars.

"Each new generation design has improved the spar concept for deepwater development," said Feijo.

The cell spar — a third-generation design — -provides the industry with continued opportunities to lower fabrication costs, again reducing the complexity of steel fabrication by simplifying the design concept, thus increasing operator flexibility in selecting where the hull can be built. The first and second generation designs, explains Feijo, required specialized shipyard fabrication, and all have been constructed in European and Far East yards and have required transport to Gulf of Mexico waters.

The Red Hawk cell spar is planned for Garden Banks Block 877 in 5,300 feet of water, representing continued deepwater advancement for spar technology, says Don Vardeman, Kerr-McGee's director of worldwide deepwater facilities. Kerr-McGee is the operator for Red Hawk with a 50 percent interest. Ocean Energy, Inc. holds the remaining 50 percent.

"We installed the Neptune classic spar in 1,900 feet of water in 1996. We followed in 2001 with installation of the Nansen and Boomvang truss spars in 3,450 feet of water. The Gunnison truss spar is planned for installation in third quarter 2003 in 3,150 feet of water. The cell spar innovations are expected to push floating technology into deeper waters," said Vardeman.

The cell spar's new hull concept features six outer cylinders or cells surrounding an inner cell, all connected by framing decks at regular intervals, rather than a single large caisson unit; a polyester mooring system, which is more buoyant than traditional chain-wire systems; and a topside-operated compressed air ballast system.

"ABS has given its 'approval in principle' of the hull design and is providing advice on engineering and inspection issues," said Feijo.

The cell spar hull will have a diameter of 64 feet, with each of the seven cylinders or tubes two feet apart and measuring 20 feet in diameter. The hull length is 560 feet and includes four heave plates to facilitate stability. Strakes or spiral vanes all along the tubes help to reduce vortex-induced vibration.

ABS also is providing insight into development of the mooring system design, says Feijo, explaining that ABS issued its Guidance Notes on Synthetic Moorings in 1999. Kerr-McGee's Red Hawk is one of the first Gulf of Mexico installations to utilize the technology.

The industry has traditionally used wire and rope chain for its mooring systems, advises Feijo. The polyester material, however, offers the industry several advantages, such as reduced mooring system weight and improved payload options. "The use of light-weight synthetic rope allows a floating production facility to support more revenue-producing equipment. The availability of synthetic materials and innovative mooring systems, such as the one being developed for Red Hawk, is extending the economic capability of existing floating technology into deeper waters," said Feijo.

ABS will class the Red Hawk spar as an XA1 Floating Offshore Installation (FOI) and the platform will maintain a U.S. Coast Guard Certificate of Inspection (COI), which ABS will facilitate on behalf of the USCG. The production facilities are not included in the classification.