Conoco Plans Tension Leg Platform For N. Sea Depths To 2,000 Feet

Conoco Inc., Houston, Texas, recently announced plans for a new type of drilling and production platform capable of operating in 2,000-foot waters, twice as deep as the previous record.

The company expects the new platform to be operating in the North Sea in four years. The first unit could cost about $1.1 billion. Officials said the "tension leg platform" will be a floating platform firmly anchored to flexible joints on the seafloor by four bundles of three 9-inch-diameter steel tubes with 3-inch-thick walls. The flexible joints and tubular lines—the tension legs—eliminate the need to solve the expensive engineering problem of inflexible legs currently unavailable in longer lengths than 1,000 feet.

Company representatives report technology already has been developed for driving the necessary piling in the deepwater seafloor to anchor the flexible joints. One advantage of the tension platform is stability. The 1,000 tons of tension on the tubes will eliminate the vertical bobbing of floating platforms, although there can be horizontal shifting of up to 79 feet.

The plan calls for 32 well slots on a floating platform with displacement weight of 56,970 tons, more than twice the size of large floating rigs already operating. "This is the first application of tension leg concept anywhere in the world," said Jack Marshall, Conoco's vice president of International Production. "It's a project the whole industry will want to watch." Mr. Marshall said the first tension leg platform will be built at an estimated cost of $1.1 billion in the Hutton Field of the North Sea, 90 miles northeast of the Shetland Islands, in about 485 feet of water.

stability company industry international president water project technology drilling Houston platform field floating