Spring 1997
Seaward Contributes to Shell Offshore’s New Gulf of Mexico Projects
Personnel from Aker Marine Contracting launch Seaward’s largest-ever SEAFLOAT foam-filled buoys for the Shell Mars Tension-leg Platform in the Gulf of Mexico.
A broad range of new technology is being used to develop deep-water oil reserves worldwide. Shell Offshore, Inc., the U.S. subsidiary of the Royal Dutch/Shell Group, is one of the principal field development leaders in advanced deep-water technology in the Gulf of Mexico. Developments include converted and new-building semisubmersibles, tension-leg platforms, spar platforms, and subsea production systems.
During 1996, Shell completed its installation of the Mars Tension-leg Platform (TLP) in record water depths in the Gulf of Mexico. The TLP is a floating platform that moves with the wind and the waves. The Mars structure, located approximately 150 miles southeast of New Orleans, measures 3,250 feet from the seafloor to the top of the drilling rig. The platform is anchored to the floor of the sea by 12 tubular steel pipe tendons, each more than a half mile long, making it the world's deepest structure. At 1/20th the weight of a conventional platform, Mars weighs 36,500 tons, with an estimated useful life of 35 years.
The Mars platform has two supply boat mooring systems, engineered and designed by Aker Marine Contracting, Houston, Texas. Each system consists of a TLP-based stern mooring system and a seafloor-based bow mooring system. The bow mooring systems comprise a buoyant synthetic rope hawser, a Seaward SEAFLOAT foam-filled buoy, approximately 3,400 feet of 2 1/2 inch catenary wire, a double parted anchor chain, and a drag embedment anchor.
The largest Seaward SEAFLOAT buoy ever manufactured, the Shell Mars buoy has a net buoyancy of 85,000 pounds and a diameter measuring 13.2 feet. Seaward SEAFLOAT buoys are manufactured using soft outer foam and rigid inner foam surrounding a steel core. They are coated with an elastomeric nylon reinforced skin and completed with top and bottom padeyes. The SEAFLOAT buoy is designed to permit deployment and recovery by a typical Gulf of Mexico anchor handling tug/supply vessel. “The buoys are needed to meet the quality standards of the high performance Mars platform”, notes Hans Treu of Aker Marine Contracting. “Shell has had good experience with Seaward buoys over the years, and the buoys offer the necessary service life”. The two mooring systems are deployed, northeast and southeast of the TLP.
Shell's newest offshore construction project, the Ram Powell TLP, under construction off the coast of Louisiana, will top the Mars record with a water depth of 3,300 feet. For this platform, Aker Marine designed a new proprietary Taut-Leg Bow Mooring System to provide significantly improved stiffness for the extended water depth. Each mooring consists of a suction anchor pile, a riser wire, a 45 kip steel submersible buoy and intermediate wire, a bow mooring surface buoy providing 105 kips of net buoyancy, and a hawser system.
Seaward has been awarded the contract to manufacture the 105,000 pound net buoyancy surface buoys, which will break the company's recent record for size and buoyancy. They will be deployed this summer.
Shell’s success in the Gulf has sparked a surge in deep-water drilling around the globe. Its deep-water projects have validated many technical advances that will be used by other oil majors and independents over the next 10 years.