Towering. Weighing over 100,000 tonnes, platform will be moved to Sakhalin Island. (Photo top courtesy of Sakhalin Energy Investment Co.)

Construction of these difficult gravity platforms was completed on time, say contractors. But costs have mushroomed, partly because of the embryonic state of design at the start of construction. "They rushed into a frontier environment," says one Sakhalin contractor. Click here to view map

Sakhalin Energy Investment Co. Ltd. declines comment while "such issues are currently under discussion with the Russian party," says a spokesman. SEIL is controlled by the Anglo-Dutch Shell Sakhalin Holdings B.V. with divisions of Japan’s Mitsui & Co. Ltd. and Mitsubishi Corp. owning the remaining 45%.

Yard Work. Structures will be located in a seismic zone and are designed for peak acceleration 2.5 times greater than the 1994 Northridge quake. (Photo courtesy of Quattro Gemini)

The platforms are destined for the Sea of Okhotsk, about 14 km off northeast Sakhalin. The first platform will tap gas from under 48 m of water of the Lunskoye field. In 30 m of water, the second platform will draw mainly crude oil from the Piltun-Astokhskoye field. It will join a converted oil rig that has been in production there for six years.

Production from the platforms will be sent to shore through new pipelines and then 800 km to Sakhalin’s south tip. Temperate weather there will allow year-round production and export of liquefied natural gas (ENR 2/17/03 p. 14).

One of Russia’s largest single foreign investments and its first offshore development, the project would have been challenging enough without the harsh physical

...environment. "The whole development is in the Pacific ‘ring of fire’...seismic conditions are well beyond normal," says Roger Swaine. He is project director for London-based Amec plc., which has a contract to design, procure and help manage topside construction.

Initially valued at $230 million, the topsides are being built by Samsung Heavy Industries in Korea, and due for delivery next March and April. Weighing around 22,000 tonnes and 27,000 tonnes, they are among the heaviest built.

Structures are designed for peak accelerations up to 2.5 times greater than those of the 1994 Northridge earthquake that devastated southern California, according Amec. On each platform’s four legs, a large friction pendulum bearing will soften the impacts of earthquake on topsides. These devices comprise top and bottom cast steel plates, both more than 3 m across, attached to the topsides and concrete legs, respectively. They are separated by a lens-shaped slider that is free to move between low-friction surfaces.

For half of each year, large ice sheets up to 2 m thick break on the concrete structures, exerting high crushing loads on the columns. To protect risers and other equipment, they are located inside the legs, making them fatter than normal. Of the...

eighing over 100,000 tonnes, Russia’s first offshore oil and gas gravity platform recently slipped out to sea from its fabrication dock at Vostochny, near Vladivostok. It is due to arrive in late June at Sakhalin Island, over 1,700 kilometers away. A second, concrete gravity structure will follow in a few weeks, establishing two key elements of a $10-billion project to tap subsea resources.