How DO you shift an oil rig that’s as heavy as 2,000 London buses?

The answer is with the world’s biggest boat — and an operation so audacious it’ll take your breath away

WHAT do you do with an offshore oil rig that is almost as tall as the London Eye and as heavy as 2,000 London buses (and that’s just the bit above the treacherous waters) when the fields of black gold run dry?

That was the challenge posed by Brent Delta when it ceased production six years ago. It was one of the first rigs built by oil giant Shell early in Britain’s North Sea oil boom, and stood 115 miles north-east of the Shetlands.

Last month, after ten years of planning and highly intricate manoeuvring in 10ft-high waves, the final, momentous act of lifting the platform from its three concrete legs took just seconds.

Now the 430ft tall, 24,000-ton ‘topside’ — the main living/working/operational area of the platform — has been brought ashore as one huge piece, complete with helipad, accommodation block that once housed 161 workers, cinema, gym, power station, drilling derricks, and all the facilities that were needed to produce and export oil and gas.

Brent Delta is the first major North Sea rig to be decommissioned at an estimated cost of £500 million. When this potent symbol of British oil’s heyday arrived at a scrapyard in Hartlepool last week — to be placed on a specially reinforced quayside that is now the strongest in Europe — its vastness attracted the crowds.

Indeed, the story of its homecoming is a jaw- dropping feat of engineering ‘firsts’, involving the world’s heaviest offshore lift by the world’s largest ship, Pioneering Spirit, which is as long as six Boeing 747s and has deck space equal to six football pitches.

Over the next year, Brent Delta will be stripped down and at least 97 per cent of its materials — including 19,468 tons of carbon steel, 82 tons of copper piping and cables, seven tons of wood, six tons of cotton bedding, five tons of glass and two tons of Formica — will be recycled.

The operation has been likened to dismantling the mother of all Meccano sets. And here we trace Brent Delta’s remarkable journey so far . . .

OIL BOOM’S BIG BABY

IN 1971, British geologists discovered the Brent oil field, midway between the Shetlands and Norway in the UK sector of the North Sea. It was named after the Brent goose which migrates from Russia along the North Sea coast. Initially, Shell named all its UK oil fields after waterbirds, including Auk and Cormorant. Oil production began in 1976 and the Brent Field, including three other platforms, Alpha, Bravo and Charlie, has produced about 10 per cent of all UK North Sea oil and gas.

At its peak in 1982, the field produced more than half a million barrels of oil a day, enough to meet the annual energy needs of around half of all UK homes at the time.

Britain’s North Sea oil output continued to grow throughout the Eighties and into the Nineties, with a dramatic effect on the local and national economy, and ending our dependence on oil imports.

But the dangers of extracting oil in the North Sea were underlined in 1988 with the Piper Alpha tragedy. A series of explosions ripped through the platform, owned by the American company Occidental Petroleum, and in two hours, 167 men lost their lives. It remains the world’s worst offshore oil disaster.

Brent Delta ceased production in 2011 and its wells have been plugged. Alpha and Bravo stopped in November 2014, and production from Charlie will end within the next few years.

While Brent Delta is the first major rig to be decommissioned in the North Sea, such removals are set to become a familiar sight.

The Brent field is just one of 470 oil and gas fields that will require decommissioning over the next 30 to 40 years. This presents the UK with a potential opportunity to become a global leader in decommissioning skills — which could later be deployed around the world. But while some of the North Sea’s most mature fields are coming to the end of their lives, this does not signal the end of the UK’s domestic oil and gas production.

The industry association Oil and Gas UK estimates that a third of the UK continental shelf’s total reserves still remain — 15-24 billion barrels of oil equivalent.

PIONEERING SPIRIT

SUCH was the rush for North Sea oil in the Seventies energy crisis, no one gave much thought to what to do with oil rigs when the fields came to the end of their lives.

The few which have been dismantled were stripped offshore, before being shipped, part by part, to scrapyards. But Shell opted for a new approach with Brent Delta — harnessing the spectacular powers of the Pioneering Spirt, the world’s largest ship.

A twin-hulled behemoth, the 1,253ft-long giant of the sea was built at a cost of £ 2.5 billion between 2011 and 2014 in South Korea, and designed by the SwissDutch company Allseas Group. It was originally called the Pieter Schelte after the Group’s owner’s father, but when it later emerged he had been a Nazi war criminal, the name was changed.

Specifically designed for removing or installing oil platforms, Pioneering Spirit is horseshoe-shaped to fit around an oil rig. It was the only vessel deemed capable of lifting Brent Delta’s topside in one piece. Its lift capacity is 48,000 tons, double Brent Delta’s weight and equal to six Eiffel Towers.

By dealing with Brent Delta, it set a new record for the heaviest single lift at sea.

THE BIG LIFT

LAST year, Brent Delta’s three concrete legs were cut above sea level, using a diamond-encrusted steel wire machine. Each 65ft wide leg — made of concrete more than 4ft thick — took a week to cut. Other pre- lift preparations included removing all loose items, installing lifting points and strengthening the underdeck.

To prevent the topside from sliding off after cutting, a temporary steel support ring was installed inside each leg to which the platform was secured.

Towards the end of last month, Pioneering Spirit was moved into position under the platform. It was a precision manoeuvre using the vessel’s state-of-the-art computerguided positioning system.

The ship’s 16 giant steel lifting beams, each weighing 1,600 tons, were then attached to points on the underside of the rig platform. The vessel faced the erratic motion of the waves, but its ‘active motion compensation’ system eliminated any movement of the beams relative to the platform.

Water was then pumped out of Pioneering Spirit’s ballast tanks, to raise her level in the water. During this phase, which took 12 hours, 80 per cent of the platform weight was transferred to the ship.

Then, in the nail-biting climax to the operation, hydraulic cylinders delivered a ‘fast lift’ — akin to the snatch lift by a weight-lifter — of the platform to a height of 3 metres above the legs in just 16 seconds.

The topside was then transported by Pioneering Spirit — top speed 14 knots (or around 16mph) — back to shore 400 miles away.

AT THE QUAYSIDE

AFTER arriving off the North-East coast, the topside was transferred to a 656ft-long, 187ft-wide barge, the Iron Lady, and was ‘skidded’ ashore at Able UK’s Seaton Port in Hartlepool, near the mouth of the Tees, on self-propelled pulleys using a system of rails.

The £ 28 million Quay 6 was designed and built over three years to accommodate Brent Delta and other rig platforms in the future. Able UK has the contract to reuse and recycle the platform’s materials and those of Brent Alpha, Bravo and, potentially, Charlie.

It is anticipated it could take 12 months to dismantle and recycle the topside of Brent Delta, involving about 50 workers. All hazard- ous materials, such as the 9,800 tons of asbestos used for insulation and gaskets, will be removed and disposed of first.

Then will begin the task of removing everything usable, from soft furnishings to pipework and girders, before its steel and equipment is sold for scrap.

Able UK’s founder and chairman Peter Stephenson, 70, said: ‘It’s the biggest single piece we’ve ever received. Firstly, we have to secure the rig to make it safe.

‘Some parts like the helicopter deck can be cut off and could be sold in one piece. Other potentially reusable equipment could include turbines, water pumps and compressors. The flare tower, where excess gas was burned off, could be taken off and used as a radio tower, depending on its condition.

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

Some steel parts such as staircases and pumps might be reusable, too. But most of the steel will be cut up and sold to steelworks, where it will be melted down and turned into steel plate (filters will remove the paint) which could then be used to make washing machines, car parts, bus shelters or construction girders.

With an average washing machine weighing 150 lb, a rough estimate would suggest there is potentially enough steel in Brent Delta to make more than 200,000 washing machine cases.

AS FOR THE LEGS . . .

This is where it gets controversial. shell has proposed leaving Brent Delta’s three concrete legs in the sea.

Each leg is almost 540ft tall, and weighs about 300,000 tons. They are surrounded at the base by 16 storage tanks (for extracted oil), each 196ft high and with the capacity of four Olympic- size swimming pools. shell argues that leaving the legs in situ is a much safer option and that the impact on the environment, when they do eventually crumble, will be minimal.

But environmental groups are, not surprisingly, concerned. The Government will decide whether to approve the plan.

in 1995, shell drew strong criticism from environmental campaigners over its plans to bury a Brent spar oil storage module in deep North Atlantic waters.

Greenpeace protesters claimed its tanks still contained oil and toxic chemicals, and occupied the rig’s accommodation, forcing shell to reverse its decision.

When these legs will collapse is difficult to predict. But shell says its studies suggest it is likely the visible parts would remain for 150 to 250 years, while the undersea sections are expected to last a further 300 to 500 years. The oil storage cells may remain largely upright for at least 1,000 years.

since February 1999, offshore facilities in the north-east Atlantic must be designed so they can be completely removed.

According to shell, for the legs to be removed completely they would have to be ‘detached from the seabed, floated to the surface and towed to shore for dismantling in a deep-water inlet or fjord. Over the past decade, [shell] has carried out a technical feasibility studies into this option. Due to the age and design of the structures, the way they are secured to the seabed and the unpredictable manner in which they could rise, we believe the risk is too great for a refloat.

‘The probability of technical failure and the risk to human life and the environment are unacceptably high.’

so for now, the legs remain.