A North Sea oil rig

Royal Dutch Shell has come under fire for plans to leave 64 storage tanks as tall as Nelson’s Column on the seabed when it abandons its Brent oilfield in the North Sea.

Environmental groups accused the company of cutting corners to save costs as a public consultation began on the biggest decommissioning project of its kind in the oil industry.

Under plans submitted to the UK government on Wednesday, Shell would remove the upper parts of its four Brent platforms in a multibillion-pound project that will deliver a windfall to the Teesside shipyard chosen to scrap the rigs.

However, Shell wants to leave behind the concrete legs, each weighing as much as the Empire State Building, which support the platforms, as well as 64 subsea storage tanks, known as cells, and drill cuttings contaminated with oil.

Government backing will be needed for Shell to secure an exemption from European rules, known as the Ospar convention, which require operators to return the marine environment to its natural state after closing down oil and gasfields.

Shell’s Brent decommissioning project is seen as an important test of those rules because it is the biggest North Sea field to be dismantled so far, with hundreds more to follow as UK oil and gas production enters long-term decline.

Lang Banks, director of WWF Scotland, a conservation group, accepted there might be a case to leave the concrete legs because of the environmental and safety risks involved in removing them. But he argued that Shell should clear the seabed of drilling detritus and storage tanks.

“The main thing preventing this from being done in this particular case is the cost,” he said. “Shell should do the right thing and remove these potentially polluting materials.”

Shell said it had consulted with 180 stakeholders over 10 years to arrive at proposals that were “safe, technically achievable, environmentally sound and financially responsible”. It said removing the cells and drill cuttings would be more environmentally risky than leaving them in place.

The Department for Business, Energy and Industrial Strategy said the plans would be “carefully considered” together with views expressed in the 60-day public consultation.

Shell is preparing to remove the 24,000-tonne “topside” of its Brent Delta platform this year. A ship the length of five jumbo jets will carry the structure to the Able yard in Hartlepool for recycling.

Brent Alpha and Brent Bravo have also ceased production and Brent Charlie is due to close in coming years. The field, 115 miles north-east of the Shetland Islands, has produced about 3bn barrels of oil since production began in 1976, equivalent to almost a tenth of total UK production.

Dismantling North Sea oil and gasfields is projected to cost over £50bn in coming decades, with about half the liability to be shouldered by UK taxpayers through tax relief that companies are entitled to claim on decommissioning expenses.

The huge costs are spurring debate over whether the clean-up requirements are too onerous. Sir Ed Davey, former UK energy minister, and Jonathon Porritt, the environmentalist, wrote in The Times last month that abandoned oil and gas infrastructure could serve as “artificial reefs” if left in place. “The evidence is that the foundations of oil and gas platforms and wind turbines, rather like shipwrecks, can provide important habitats for valuable marine species,” they wrote.

Others insist the rules should not be watered down. “Companies operating in the North Sea have a legal, as well as moral, obligation to clean up their mess,” said Mr Banks. “Having once pushed the boundaries of science and engineering to secure the oil and gas beneath the seabed, the industry should be pressed once again to do the same when decommissioning.”

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