NKK Completes World's First Offshore Steel/Concrete Drilling Platform

The world's first composite steel/ concrete offshore drilling platform, a 59,000-ton giant fabricated and assembled in Japan for an American owner, is destined for oil and gas exploration in the Beaufort Sea near Alaska's North Shore.

Named the Glomar Beaufort Sea I, the concrete island drilling system (CIDS) was built by Nippon Kokan (NKK) in only nine months after order placement, and turned over to its owner/designer/operator, Global Marine Development, Inc. of Newport Beach, Calif., recently.

Six days after delivery, GDMI, a subsidiary of Houstonbased Global Marine, Inc., began towing the huge structure from Japan to Point Barrow, Alaska, for August transshipment east to Harrison Bay during the brief summer thaw. Initial drilling operations for the CIDS are scheduled for November this year.

Nearly as tall as a 10-story building at 95 feet high, with a square deck of nearly two acres (87,000 square feet), the CIDS is built like a towering steel-concrete- steel sandwich. The structural steel base, which will rest on the sea bottom, supports a midsection fashioned from lightweight concrete, atop which is attached a steel deck barge containing crew quarters and six primary drilling modules.

Global Marine Development chose the hybrid steel/concrete design to utilize steel's strength and concrete's durability to resist the Arctic's rugged environment, which can include ice more that six feet thick, temperatures as low as minus 58 F, and winds of more than 100 mph. In service, the CIDS's steel base will be completely submerged, shielding it from the effects of wave action and contact with floating ice.

The concrete center section is expected to provide long, minimum- maintenance service in spite of the severe operation conditions it will encounter. A pair of deckmounted 10,000-gpm water guns will be used to break up approaching ice floes to create a cushioning barrier of ice rubble around the concrete structure.

NKK fabricated approximately 12,000 tons of a newly developed, low-temperature-service plate steel from which it erected the base structure. A lattice spike board will help hold the CIDS in place and transmit ice pressures against the sides of the structure on the ocean floor. NKK also built the upper deck barge, including the six primary drilling modules. The latter work was performed under a contract awarded by Parker Drilling Company of Alaska.

Under the supervision of NKK civil engineers, the 35,000-ton concrete component with honeycomb core was constructed by a joint venture of Penta-Ocean Construction Company and Shimizu Construction Company. Design provisions have been made to add a second concrete segment if the CIDS is to be operated in waters deeper than 55 feet.

Other stories from September 1984 issue


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