Energy giant Shell has unveiled detailed plans for decommissioning its Brent oil and gas field, 40 years after it began production.
The Brent field, located north east of Shetland, has been operating since the 1970s.
In its lifetime, it has generated more than £20 billion in tax revenues for the UK government and provided around 10 per cent of the nation’s oil and gas.
But three of the four massive drilling platforms – Alpha, Bravo and Delta – have reached the end of their useful life and must now be removed.
The operation will cost billions of pounds and could take up to a decade to execute.
The company intends to cap 154 wells, remove the upper parts of the platforms, recover debris lying on the seabed and extract oil trapped in underwater storage cells.
Concrete structures, including the legs supporting the platforms, will not be removed.
The decision to leave parts in place has been made on the basis that the environmental benefits of removal would not outweigh the safety risk for offshore workers carrying out the task.
“After an extensive and in-depth study period, the submission of Shell’s Brent decommissioning programme marks another important milestone in the history of the Brent oil and gas field,” said Duncan Manning, decommissioning asset manager for Brent.
“Shell has undertaken thorough analysis, extensive scientific research and detailed consultation with over 180 stakeholder organisations over the past ten years.
“Working within the tightly defined regulatory process, we believe that our recommendations are safe, technically achievable, environmentally sound and financially responsible.”
The plans have been unveiled on the same day that First Minister Nicola Sturgeon announced a new £5 million fund to help Scottish workers to benefit from the decommissioning process.
Around 470 more UK oil and gas installations in the North Sea are expected to reach the natural end of their lives over the next three decades.
Decommissioning is regulated by the Convention for the Protection of the Marine Environment of the North-East Atlantic, known as the OSPAR Convention.
But environmentalists have raised concerns over Shell’s proposals for what will be the first major decommissioning project in the North Sea.
“Oil and gas companies operating in the North Sea have a legal, as well as moral, obligation to clean-up their mess,” said WWF Scotland director Lang Bank.
“Having once pushed the boundaries of science and engineering to secure the oil and gas beneath the seabed, the industry should show the same innovation when it comes to decommissioning.”
He added: “The OSPAR agreement is there to make sure the marine environment is protected and should be followed. The rules already allow for companies to seek permission to leave some material behind - such as the massive concrete legs - where moving it would pose an unacceptable risk to staff or the environment. We accept this principle.
“If the oil within the cells and some of the drill cuttings occur above limits that internationally agreed standards recommend, then they should be removed in order to prevent damage to the environment.
“The main thing preventing this from being done in this particular case is the cost. Shell should do the right thing and remove these potentially polluting materials.”
The plans have been submitted to the UK Department for Business, Energy and Industrial Strategy and a 60-day consultation has been launched.