BP has achieved a key milestone on its Greater Tortue Ahmeyim (GTA) liquefied natural gas project offshore Senegal and Mauritania after the construction of 21 concrete caissons that make up a breakwater was wrapped up this month.

Located on the maritime boundary of the two countries, about 110 kilometres from the city of St Louis, this breakwater is vital because it will protect GTA’s key infrastructure — a floating LNG vessel plus utilities and accommodation platforms — from Atlantic Ocean swells.

France’s Eiffage Civil Marine built all the caissons at a purpose-built site in Dakar, with the structures towed to a deep-water holding site just off Goree Island from where they were transported about 150 kilometres north to the GTA location.

As of 9 February, 16 of these caissons had been installed offshore.

For construction, more than 130,000 cubic metres of concrete were produced by two plants operated by Eiffage in Dakar, while 30,000 tonnes of steel were also needed.

Each caisson weighs more than 16,200 tonnes and is 55 metres long, 28 metres wide and 32 metres high.

According to Eiffage, the construction activities involved more 1700 people, 97% of whom were Senegalese.

Eiffage is now helping construct a gas transfer platform for GTA.

Due on stream in 2023, phase one of the GTA scheme involves deep-water subsea wells sending gas and liquids to a floating production, storage and offloading unit moored on the continental shelf.

Liquids will be offloaded onto shuttle tankers, with gas piped to Golar LNG’s 2.5 million tonnes per annum floating liquefaction unit for subsequent export.

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