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-Astokhskoye-A (PA-A) — known as ‘Molikpaq’ after the Inuit word for ‘big wave’ — started year-round production in December 2008 and had an average daily production rate of 6.72 thousand tonnes (49.49 thousand barrels) of oil and 0.83 million cubic metres of associated gas in 2016. At the end of 2016, the operating well stock of the Molikpaq platform included 15 wells, five water injection wells and one intake well for re-injecting drill cuttings back into the reservoir.

At the Lunskoye-A platform, gas is produced from the largest diameter wells ever drilled in Russia. In 2016, two additional production wells were drilled and completed, bringing the total number of wells to 15. The platform’s average daily gas production rate in 2016 was 45.68 million cubic metres per day.

Piltun-Astokhskoye-B (PA-B) is the biggest offshore platform in the Sakhalin-2 project. At the end of 2016, the PA-B platform had 13 production wells, seven water injection wells, and two cutting re-injection wells. The platform’s average daily production rate in 2016 was 3.94 thousand tonnes (29.05 thousand barrels) of oil and 1.17 million cubic metres of gas.

A 300-kilometre undersea 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 production 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.

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