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Platforms withstand ice, earthquakes
A few kilometres off Sakhalin Island stand three huge oil and gas platforms. They can withstand storm-whipped waves 10 metres high in spring and autumn, typhoons in summer and the enormous pressure of ice floes in winter. And they lie in the world’s most active earthquake zone.
Drilling is under way at the Lunskoye-A platform to the north-east of Sakhalin Island. Two wells are already producing gas at some 10 million cubic metres a day each, a rate equalling the current offshore world record. A third well is ready for production and a fourth is almost complete. When the platform reaches full capacity, it will produce more than 50 million cubic metres a day of gas, and 50,000 barrels a day of natural gas liquids.
To the north of Lunskoye-A at the Piltun Astokhskoye-B (PA-B) oil platform, two wells have been drilled and are producing a combined 24,000 barrels of oil. More wells are yet to come. The platform was designed to produce 70,000 barrels of oil and three million cubic metres of gas a day. A third platform, Piltun-A (PA-A) — known as “Molikpaq” after the Inuit word for “big wave” — has produced more than 100 million barrels of oil since 1999 during ice-free months only. It started year-round production in December 2008.
Installation world record
Two specially built T-shaped barges, each the size of two football fields, towed the upper parts, or topsides, of the PA-B and Lunskoye-A platforms 3,000 kilometres from the Samsung Heavy Industries shipyard in South Korea where they were built.
The barges sailed into position between already-installed platform legs before being gradually lowered, allowing the topsides to settle on the legs. The PA-B’s 28,000-tonne topside makes it almost as heavy as three Eiffel Towers — it set a world record in 2007 for the heaviest topside ever installed this way. The fully assembled platform is as tall as a 30-storey building.
Ice-breaking platform legs
The platforms’ giant concrete legs — each wider than 20 metres and some 56 metres tall — were built in Vostochny port in Russia in December 2004 and towed to the site on a barge pulled by three tugboats. They are extra thick to help withstand earthquakes and their rounded shape helps ice floes slide around them. “It sounds like an icebreaker ripping through pack ice and it makes the platform gently rock,” says Egbert Menzinga, chief technician on the PA-B platform. Sometimes sheets of ice edge up platform legs, peel backwards and crash back down on the frozen sea. The pressure of the ice against the four legs can amount to 30,000 tonnes.
A structure used to protect bridges and public buildings from earthquakes was installed in offshore platforms for the first time. Two of Sakhalin II’s platforms are connected to their concrete legs by sliding joints. If an earthquake strikes, the topsides can move independently from the legs in a pendulum motion, preventing damage. The design can withstand an earthquake measuring 8.0 on the Richter scale — greater than the strongest earthquake expected to occur around the platforms. Such an earthquake may occur on Sakhalin Island perhaps once in 3,000 years. A similar design protects San Francisco’s Oakland Bay Bridge and Istanbul’s Ataturk Airport.
A 300-kilometre under sea pipeline network links the three platforms to an onshore processing facility. An onshore system of 1,600 kilometres of pipelines takes the oil and gas to an LNG (liquefied natural gas) plant and oil export terminal, both at the Prigorodnoye complex at Aniva Bay in the south of the island.
Protecting western gray whales
A small population of western gray whales, a species once thought to be extinct, feed off the coast of Sakhalin Island in the summer months. To protect them, sound levels in the area are monitored and work such as carrying out seismic surveys and pipe laying is suspended when the noise exceeds levels recommended by the Western Gray Whale Advisory Panel. Buoys with acoustic monitors positioned along the edge of the feeding grounds track sound levels during such work. Other measures to keep disturbance to a minimum include carrying out seismic surveys as soon as ice breaks up before the whales’ feeding season, limiting the number of ships in the area, setting speed limits, and using navigation corridors.
The International Union for Conservation of Nature’s (IUCN) independent scientific review panel works with Sakhalin Energy to study the whales’ habits and monitor the impact of offshore operations. In recognition of its western gray whale protection programme, Sakhalin Energy won the 2008 Environmental Project of the Year award from Russia’s Ministry of Environment and Natural Resources.
