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Platforms withstand harsh climate, 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.
The first Russian offshore platform, Piltun-A (PA-A) — known as “Molikpaq” after the Inuit word for “big wave” — had an average production rate of 45 thousand barrels of oil and about 1.5 million cubic metres of gas per day in 2010. It started year-round production in December 2008. There are thirteen oil production wells, four water injection wells, one gas reinjection well and one waste disposal well on the platform.
At the Lunskoye-A platform, gas is produced from the largest diameter wells ever drilled in Russia. Two new gas production wells were completed in 2010, which brought the total number of wells to seven. The Lun-A gas production rate is up to 10 million cubic metres of gas per day per well.
Piltun-Astokhskoye-B (PA-B) is the biggest offshore platform in the Sakhalin-2 project. Two oil production wells and three water injection wells were drilled in 2010 thus bringing the number of oil wells on the platform to eight. Two new water injection wells will be drilled by the end of 2011.
A 300-kilometre under sea pipeline network links the three platforms to an onshore processing facility. From there 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.
Ice-breaking platform legs
PA-B and Lun-A 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.
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-2’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.
Installation world record
In 2007, 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.
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.