Oil and gas production from the UK sector of the North Sea peaked at the end of the last century and has been in steady decline ever since. Most of the large oil and gas fields are now either depleted or approaching their economic limits, and the various oil and gas producers are now actively involved in large-scale decommissioning projects. Given the scale of the oil and gas industry infrastructure in the North Sea, it appears that decommissioning will be a major source of complex and expensive projects for decades to come. The decommissioning process has also been accelerated by the recent but sustained fall in global oil and gas prices.
Decommissioning projects in the North Sea generate unusual and highly variable risk profiles, and in some cases the engineering challenges appear almost insurmountable. A good example is the current strategy adopted by Shell in decommissioning the Brent field infrastructure. This programme of projects is scheduled to last at least 10 years and the works are regulated by the UK government’s Department of Energy and Climate Change (DECC).
There are four main production platforms in the Brent field. They were designed in the 1970s when demand for energy was high and the priority given to eventual decommissioning was low. The platforms feature topsides supported on legs that sit on gravity base structures. The gravity base structures are enormous. They are made of reinforced concrete and steel, weigh around 300,000 tons and are anchored to the seabed. It is difficult to see how these could ever be completely removed.
Shell, therefore, has applied to the DECC for a relaxation to regulations and proposes to leave much of the gravity base structure in situ, where it will remain for thousands of years. Consideration is now being given to this proposal, and a range of interested parties, from the Scottish Green Party to the World Wildlife Fund, are already expressing their opinions on the potential environmental impact of the proposal.
The Brent field decommissioning programme is a good example of project success criteria changing over the course of the project lifecycle. Since 1999 all North Sea infrastructure has had to be designed for eventual complete removal. Removal was not considered a priority in the 1970s, however, and the legacy of that approach is having a major impact on the industry today.
If you are interested in the risks and challenges posed by the Brent field decommissioning programme, you can read more about it here.