One of the oldest and largest oil rigs in the North Sea has been successfully brought ashore after 40 years at sea.

The 44 metre-tall, 24,000 tonne Brent Delta platform will be cut into pieces to be sold for scrap, in a process lasting around 18 months.

It's the first of four rigs to be decommissioned in the Brent field around 115 miles northeast of the Shetlands and the major engineering challenge is being watched closely by industry and environmentalists.

The project started on Friday when the largest ship in the world, Pioneering Spirit, carried out the largest-ever marine lift.

The topside of the oil rig was removed in one piece from its concrete legs.


It took years to plan but the specially-designed ship took just 10 seconds to raise the platform off the base.

Image: Pioneering Spirit carried out the largest-ever marine lift

Now work begins at Able Seaton Port in Hartlepool to reverse-engineer the structure.

A team of around 50 engineers hope to dismantle the topside and recycle 97% of the material.

Peter Stephenson, executive chairman of Able, said this is the biggest decommission work ever to be carried out from the North Sea.

Normally pieces of rigs are transported in weighing no more than a few thousand tonnes but this is an entire rig.

He told Sky News: "It's a huge task and firstly we have to secure the rig to make it safe as we have never worked at these sort of heights.

"Some parts like the helicopter deck can be cut off and sold in one piece but then we need to go through it internally and take out pipes, wiring and soft furnishings.

"Then the real work begins as we get the heavy cutting equipment and begin taking it apart from top to bottom."

More than 100 platforms are forecast to be completely or partially removed over the next decade in the waters of the UK and Norway.

Image: The specially-designed ship took just 10 seconds to raise the platform off the base

The Brent field is one of the largest fields in the North Sea and is responsible for about 10% of total North Sea production during the past four decades.

At its peak, the four rigs were pumping 500,000 barrels of oil out of 154 seabed wells every day.

Decommissioning the field will be a major infrastructure project and is being closely watched by the industry because it is the biggest North Sea field to be dismantled so far, with hundreds more to follow.

It is also being closely watched by environmental groups who have already expressed concerns about Shell's planning process.

WWF Scotland and seven other environmental organisations have claimed the oil giant's proposals contain "insufficient information" and could breach international rules.

Such rules state all oil rig elements must be removed once a platform has finished work but exceptions can be made in certain circumstances.

Shell's plan, which is being considered by the international regulator, is to leave the concrete legs of three of the four decommissioned rigs on the seabed.

Welcome aboard the world's biggest boat

Lang Banks, of WWF Scotland, said: "There are very clear international rules setting out what Shell have to do in order to prove their case to leave these materials on the seabed.

"Unfortunately in this case we don't believe Shell have adhered to those rules and they're going to have to go back and think again."

Shell's Alastair Hope said: "We've demonstrated that we've done the right thing by removing the topside and we'll do this will all our Brent rigs.

"If there is hazardous waste, it's in the topsides, it's not in the legs. We're doing it with new technology and we're doing it in a safe, cost efficient and environmentally friendly way."