Shell wants to decommission oil platforms in the North Sea

Shell raises the white flag and starts dismantling its oil platforms in the North Sea in 2017. A good piece of news that hides a sad environmental lagacy.

Shell is ready to dismiss its oil field’s four platforms in the North Sea, 115 miles north-east of the Shetland Islands. First step in 2017: dismantling the Brent Delta platform which will be remembered as the first large-scale project to decommission a depleted North Sea oil field. Second step: decommission the other three platforms, Alpha, Bravo and Charlie.

After planning the dismantling activities and transportation of the materials for 10 years, the start of the complex work has been delayed to 2017, according to Reuters. In fact, it took longer than expected to equip the specialist vessel that will transport the 25,000-tonne platform to Hartlepool harbour where it will be disassembled. Once it reaches its destination, the platform will be demolished and recycled. This is a huge work considering that Brent Delta is as tall as the Eiffel Tower (according to Shell).

The most widely discussed issue is exactly the plan for the removal of the Brent Delta. In fact Shell just wants to remove the topsides of the platforms and leave the concrete and steel base structures, 64 tanks and an unknown number of pipes and debris generated by drilling.

The Brent oil field

The platforms of the Brent oil field are made of three or four concrete legs that are about 165 metres long, 18 metres in diameter and rise to 25 metres above sea level. At their base there are 64 tanks or ‘subsea cells’ which had been used for oil storage, made of reinforced concrete that are 20 metres in diameter and 60 metres tall (taller than Nelson’s Column in Trafalgar Square and each with the capacity of four Olympic-size swimming pools).

Over the course of the years, 42 tanks have been used to store oil and once the platforms will be dismantled they will remain in the North Sea bottom entombed in thick walled concrete pyramids, according to Shell.

The multinational corporation came up with this solution after examining different methods for cleaning the tanks, without obtaining encouraging results. This is a delicate issue since these concrete tanks contain a highly polluting mixture of oil, water and a layer of debris. Disassembling and transporting them is so difficult and risky so Shell had to turn to NASA, even though in the end it decided to leave the tanks in the sea bottom. Besides the platforms of the Brent oil field, there are 140 wells and 103 kilometres of pipelines that will be left where they are.

oil platform
Dimension of the Brent oil platform compared to some monuments. Photo via Shell

A sad legacy for 40 generations of Scots

In the presentation of its dismantlement plan Shell says it will use innovative techniques, ensuring the safety of people working on the project, having minimal impact on the environment and being economically responsible. But how long will it take for these materials to decompose? Shell itself provides an assessment.

The concrete legs above sea level will take between 150 to 300 years to disintegrate. The legs below sea level will take up to an additional 500 years to fall apart. And what about the 64 storage cells? They can take up to 1000 years to decompose.

In other words, if the Shell proposals are given the green light by the UK Government and by OSPAR, a body set up to safeguard the North-Atlantic environment, the platforms will affect Scots for the next 40 generations.

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