Taking down the North Sea platforms one by one

London

Royal Dutch Shell plans to decommission the North Sea’s Brent oilfield — one of the UK’s biggest — in a multibillion-dollar project over the next 10 years that could be followed by other closures after the plunge in oil prices.

The Anglo-Dutch energy group will within days begin public consultation on a disposal plan for the “topside” of Brent Delta — one of four platforms in the field that gave its name to the international crude price benchmark. Shell is anxious to avoid a repeat of the public furore 20 years ago over its attempt to dump the Brent Spar oil storage buoy in the Atlantic Ocean.

The decommissioning of Brent Delta will involve lifting its 23,500 tonne steel superstructure that stands high above the waves — and includes the drilling rig and multi-storey accommodation block — on to a giant ship called the Pieter Schelte. Shell executives say this will be the biggest offshore lift ever attempted, and could be a template for dismantling many of the North Sea’s larger platforms.

The topside structure will then be taken by the Pieter Schelte to Teesside, where much of it will be scrapped and recycled into washing machine parts. But Shell will take more time to decide whether — and how — to remove Delta’s huge concrete legs and oil storage tanks. The bigger subsea structure, in water 140 metres deep and weighing 300,000 tonnes — as much as the Empire State Building — would take thousands of years to erode if left in place.

Shell says the lifting of Delta’s topside, likely to happen next year, will “substantially reduce the risk, cost and environmental impact of the operation” — and is preferable to taking the structure apart piece by piece in the North Sea.

However, David Santillo of Greenpeace warns that the second stage of the process, involving what to do with Delta’s concrete legs and underwater storage tanks, is key. “Shell should take full responsibility for the waste they have generated and not leave anything on the seabed that is possible for them to recover,” he says. The World Wildlife Fund has similar concerns.

Shell’s 30-day public consultation on Brent Delta, comes against a backdrop of a more than 50 per cent drop in oil prices since last summer that could encourage other North Sea operators to mothball uneconomic fields and even accelerate decommissioning plans.

Almost all the North Sea’s remaining 470 platforms, as well as 10,000 kilometres of pipelines and 5,000 wells, will be decommissioned over the next 30 years, with companies expected to spend 40 billion pounds by 2040. Shell alone has more than 30 platforms. Thousands of jobs could be created as others are lost — 200 will be employed to dismantle the Delta onshore.

ConocoPhillips is among those that could follow Shell. The Financial Times understands it has submitted draft plans to the UK’s Department for Energy and Climate Change for a phased withdrawal from the southern North Sea, where gasfields that came on stream in the 1970s are nearing the end of their lives. It is thought the company has secured permission to halt output at some fields.

Lying nearly 200 kilometres east of the Shetlands on the edge of Norwegian waters, the Brent field, discovered in 1971, is nearing the end of its life after almost 40 years of production that helped turn the UK into an oil exporter.

Though not the first of the UK’s offshore fields to be decommissioned, Brent will be the biggest so far. And Delta, which ceased production in 2011, will be the first of the four platforms to be dismantled.

Engineers and construction workers are now busy preparing for the removal of Delta’s topside structure, which will separated from the legs using diamond wire cutters.

If all goes to plan, the Pieter Schelte ship, five times longer than a Boeing 747, will come up either side of Delta and extend powerful, hydraulic arms underneath it. Then, in just 10 seconds, it will raise Delta’s topside structure 3 metres clear of the legs, and take it 380 miles to Hartlepool in northeast England.

There, the topside will be dismantled by Able UK, the decommissioning specialists. Shell says that 97 per cent of the topside will be recycled. Alistair Hope, Shell’s project director for the Brent field decommissioning, says the company has learnt the lessons of Brent Spar and consulted widely. He argues that the Pieter Schelte is the answer to how operators will remove infrastructure that was never designed to be taken away.

“This is game-changing technology. It offers a new option and, for the very large platforms like the Brents, this might well be the best way to go,” he says.

Delta’s legs, each 170 metres tall, 18 metres wide and embedded several metres into the sea floor, are another matter, however. Next to them on the seabed stand 16 storage cells, each 60 metres high and able to hold enough oil to fill four Olympic swimming pools.

Under the Ospar convention governing the North Sea, operators are obliged to remove the entirety of their platforms, including the legs. However, Shell could seek an exemption.

In practical terms, Shell is likely to face two options. Either the company leaves the legs in place, above the surface with navigation lights, or cuts them away 50 metres below the surface, meeting maritime rules to protect shipping. That would involve another first — removing blocks of reinforced concrete, each the size of Big Ben.

Financial Times