The Brent field is situated in the North Sea 116 miles offshore, north-east of Lerwick, Scotland. It consists of four large platforms; Alpha, Bravo, Charlie and Delta. After 40 years of producing oil and gas, the field is now being taken out of service, or ‘decommissioned’.
Decommissioning Brent is a complex, major engineering project, because of its size, age, the type of infrastructure, and the harsh environment of the North Sea. Our recommendation for Brent is to remove the topsides of the four platforms to shore for recycling, leaving the legs in the sea.
Our recommendations are the result of 10 years of research, involving more than 300 scientific and technical studies. We established an independent group of scientific experts to review the findings and ensure all feasible decommissioning options were investigated thoroughly. We submitted our recommendations to the UK Government following extensive stakeholder engagement involving over 180 different organisations, and only when we were confident that they were safe, technically achievable, environmentally sound and socially and economically responsible.
Once the topsides have been removed, the concrete legs (called gravity base structures) which are part of Bravo, Charlie and Delta would be left in place. Studies predict that the legs would degrade slowly over hundreds of years as the seawater penetrates the concrete and the reinforcing steel bars within begin to corrode. According to independent analysis, this slow process of degradation and corrosion would have no measurable impact on the environment. Small pieces of concrete could separate from the legs and fall to the seabed or on top of the cells over time.
Our recommendations are the result of 10 years of research and independent verification. While removing the legs may feel like the right thing to do, the risk to people and the environment is not justified given the small impact of leaving them in place.
We know the sediment contained in the base of the concrete storage cells on Bravo, Charlie and Delta contains no significant non-biodegradable compounds. It is a sticky mixture of about 50% water, 25% sand and grit, and 25% oil particles attached to the sand and grit. It does not flow and is difficult to move. Independent laboratories have scrutinized the samples.
We studied two options for removing the sediment; to remove and inject it into subsea wells, and one to pump it into tankers and take it to shore. Both would be technically difficult and present significant safety risks to people working on them, on balance with only a minor benefit in terms of reducing the legacy environmental impact.
As required by law, our proposals are based on the criteria of whether they are safe, technically achievable, financially and socially responsible, and environmentally sound, as stipulated by the Department for Business, Energy and Industrial Strategy.
An Independent Review Group (IRG) provided peer review of the quality of the studies carried out, and Shell engaged extensively with a wide range of stakeholders to share the recommendations to understand any issues or concerns.
As part of the Brent decommissioning programme, we are removing the structures above the water, called topsides.
Removing each topside is a major engineering feat. The Brent Delta topside was removed in April 2017. This single lift of the 24,200 tonne platform by the Pioneering Spirit marked the world’s heaviest offshore lift, by the world’s largest construction vessel. Then, in June 2019, the 25,000 tonnes Bravo topside was also removed. The structures have been taken to Hartlepool where around 98% of all materials from Delta have already been recycled.