Ekofisk protective barrier

Year:1989

Duration:18 months

Cost:£1.06bn (£2.5bn today)

Country: North Sea, UK

What did this project achieve?

Stop a million-barrel undersea oil storage tank from being damaged by subsidence

Ekofisk is one of the biggest oil fields in the North Sea. About 320km south of Stavanger in Norway, it was discovered in 1969 by the Phillips Petroleum Company (now ConocoPhillips). The field is expected to produce oil and gas until 2050.

The Ekofisk complex is a series of interconnecting rigs and platforms at the centre of the Ekofisk field. Oil from the complex is transported to a terminal at Teesside in the UK. Gas is piped to a terminal in Emden, Germany.

The Ekofisk tank is at the centre of the complex. The tank was the world’s first concrete offshore oil platform. It can store 1m barrels of oil.

Major subsidence was detected in chalk deposits in the seabed under the Ekofisk complex in 1984. Engineers calculated that subsidence would eventually be as much as 6m. This would make the complex vulnerable to impact from waves.

A team headed by ICE member Peter Broughton came up with a design for a protective barrier for the Ekofisk tank. Looking a bit like a circular fort and made of concrete, it was constructed in two semi-circular segments which fitted together around the tank.

The protective barrier reduced wave impact to the tank and helped secure the Ekofisk complex’s future as an oil-producing field.

Difference the barrier has made

Daily production of oil and gas at Ekofisk varies but it’s often more than 300,000 barrels of oil a day. This oil is worth £12m – or £4.38bn in a year.

If production at the platform had to stop, it would mean closing down the Emden gas terminal in Germany and the Teesside oil plant.

Any interruption to continuous production would have had a major financial impact on workers and their employer.

vThis meant it was essential to construct the protective barrier without interrupting production. The project achieved this, as well as protecting output for the future.

 

How the barrier was built

Engineers built the protective barrier in two semi-circular sections at Alfjorden, a fjord in Norway.

At 106m high and weighing 125,000 tonnes, the barrier was designed to have an outer diameter of 140m when assembled. Each half unit had 24 cells – these would be filled with gravel ballast at Ekofisk.

The two halves had to arrive at Ekofisk close together. This meant using two towing fleets – a total of 18 vessels.

Getting the barrier segments to the complex was a delicate business. The two huge structures passed as close as 10m to platforms and rigs on the way.

The two halves were connected together round the Ekofisk tank. Engineers filled the 24 cells in each unit with 1m tonnes of gravel ballast to keep the barrier firmly on the seabed.

The barrier was installed without having to shut down production.

"​‌

It is unique.It's as spectacular as the Great Barrier Reef and the Great Wall of China, so we just call it the Great Barrier Wall.

Burt Smith

director of Phillips Norway's special projects group, 24 September 1989

Fascinating facts

Each half unit of the barrier has a unique shape and mass from anything previously constructed.

The barrier protects against greater wave impact than any other marine structure.

The Ekofisk Bravo platform saw the biggest ever blowout in the North Sea in 1977. The blowout – an uncontrolled release of oil losing the equivalent of more than 80,000 barrels – was eventually capped by oil rig firefighter Paul Neal ‘Red’ Adair and his team.

People who made it happen

  • Lead project engineer: Dr Peter Broughton, ICE Fellow

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