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North Sea—what lies beneath

Shell wants to leave some of its defunct Brent infrastructure at sea. It’s the cheap way to decommission—but might also have ecological benefits

The successful removal of the topsides from the Shell's Brent Delta platform in April was a symbolic affair. That's not just because it was one of the biggest such operations ever undertaken on one of the industry's more iconic structures, now destined for scrap and recycling. Just as important was what was left behind—three massive concrete legs, reinforced with steel, sitting on the seafloor in water 140 metres deep. Their fate is a subject of intense debate.

At its peak, in the early 1980s, Brent Delta and its three sister platforms on the Brent field produced over 0.5m barrels a day of oil between them—and spawned the Brent crude benchmark price. Its removal represents the largest piece of North Sea decommissioning yet and is a potent reminder of an oil province's decline.

The operation far exceeded anything that Allseas' vessel Pioneering Spirit had been employed for before: Brent Delta's 24,000-tonne topsides dwarfed the lift of Repsol's 13,000-tonne platform offshore Norway last year.

It also highlights the trend towards moving defunct platforms to shore in one piece for disposal, rather than dismantling them in place. The platform, which was located 186km off the coast of northeast England, was transported back to land before it was moved onto a barge and taken to the Able UK shipyard at the mouth of the River Tees, near Middlesbrough.

But that's not the end of the journey for Shell. There remains the thorny issue of what to do with the gravity-base structure (GBS) that supported Brent Delta, which includes the legs and associated infrastructure, such as storage cells at the bottom. The whole structure is estimated to weigh around 300,000 tonnes.

Shell wants to do a further clean up, but leave the legs in place, claiming they would not harm the environment and that the disturbance caused by removing them could do more harm than good. Others say Shell should completely clean up the mess it created and abide by the internationally agreed regulations governing decommissioning, which state all infrastructure should be removed wherever possible.

Shell certainly has a financial interest in leaving the legs in situ, making the company an easy target for groups that have a track record of questioning its motives regarding decommissioning. Shell came a cropper in the 1990s, when a campaign led by eco-activist group Greenpeace blocked the company's plan to dump the Brent Spar oil-storage module in the sea. Since then, there has been little love lost between Shell and non-governmental organisations like Greenpeace and Friends of the Earth, which tend to mistrust the company (and its peers).

It's no surprise that an oil company might be acting in its own interests. But, on this occasion, such criticism may be unfair.

"The vast majority of rigs installed in the North Sea were put in without much thought about how they were going to be removed," says Ben Wilby, a decommissioning analyst at Douglas Westwood. "We don't know exactly how much it would cost to remove GBSs like those used in the Brent field, but it would probably be the sort of amount that could bankrupt some companies. I can't see how it can be done."

The consultancy estimates that the total spend on UK decommissioning by 2040 will be £42bn ($55bn)—and that's assuming that GBSs are left in situ.

The cost of decommissioning doesn't just accrue to the companies involved. Wood Mackenzie, another consultancy, has estimated that not far short of half of the total North Sea decommissioning bill would be paid by the UK taxpayer in the form of tax relief to the oil and gas industry. That amounts to about £24bn of the £53bn that Wood Mackenzie estimates will be spent on decommissioning North Sea infrastructure over coming decades.

Rigs-to-reefs

Meanwhile, the idea that the legs could be left in the ocean without much environmental damage—and with some potential benefits—is one ocean scientists say is realistic, and also countenanced by some environmental campaigners.

Decommissioned oil structures can be positive for the environment by providing a habitat for marine life as a kind of artificial reef. Studies in the North Sea report that some structures are swiftly colonised and develop productive ecosystems based around cold-water coral.

The rigs-to-reefs idea is already well established in the US, underpinned by research offshore California and in the Gulf of Mexico (GoM), and backed by the US Bureau of Safety and Environmental Enforcement (BSEE). According to the BSEE, 470 platforms had been converted to permanent artificial reefs in the GoM by July 2015. The organisation cites studies showing an eight-leg structure typically provides a home for 12,000 to 14,000 fish.

All this research comes with caveats, stressing that each rig needs to be assessed individually for suitability, and that the environmental impacts of oil-filled sediments and cuttings that lie underneath oil and gas installations are not fully understood.

A team at the UK's National Oceanography Centre, based in Southampton, is developing marine robots to find out more about the impact of this detritus and of the impact in the seafloor of removing oil infrastructure, which could disturb a recovering environmental system. The team, led by Daniel Jones, notes that there is no standard approach for making environmental-impact assessments for decommissioning in the North Sea and that current assessments have not led to clear conclusions.

The evidence in favour of leaving some infrastructure on the ocean floor has been strong enough to persuade some environmental campaigners that it is worth investigating further.

Jonathan Porritt, an environmental activist and former director of Friends of the Earth, and Ed Davey, a former UK energy minister, co-wrote a letter to the Times newspaper in January urging further research before forcing companies to remove all seabed infrastructure.

"There isn't yet consensus on a 'new best decommissioning practice' to take account of this science. But before we spend billions removing potentially valuable habitats we should find out," they wrote.

What happens next depends to a large degree on decisions based on a regulatory mechanism drawn up for the industry in the 1990s, known as the Convention for the Protection of the Marine Environment of the North-East Atlantic (Ospar) to which the EU and 15 individual countries, including the UK, are signatories.

Ospar was designed to ensure the removal of major oil-industry infrastructure at the end of its life. But it also allows for governments to request exemptions—known as derogations—if they can show there are significant reasons why an alternative form of disposal for infrastructure, such as concrete structures, is preferable to leaving them in place.

Waiting on a decision

Shell's plans for the Brent field decommissioning, submitted in February, do entail a request to leave in place the GBSs of three of its Brent platforms—Bravo, Charlie and Delta—along with some of the content of the cells and drill cuttings. The wider field decommissioning also involves removal of pipeline infrastructure and the plugging and securing of 154 wells.

Shell also wants to leave the lower section of Brent Alpha's structure, a 31,000-tonne steel jacket rather than concrete, removing only the top, down to 85 metres below sea level. Some analysts believe the case for leaving predominantly steel structures in place in the North Sea may be harder to make, given they are lighter than a GBS and some have already been completely removed effectively. A 60-day consultation on the plans closed in April and was still under consideration by the government in May.

Environmental groups criticised the plan for providing insufficient information, claiming it was too subjective, lacking quantitative analysis based on hard data. WWF Scotland was among them but its director, Lang Banks, said he accepted the principle that companies could seek permission to leave some material, such as concrete legs, behind, where moving it would pose an unacceptable risk to staff or the environment.

But commenting on Shell's plans in February, he said this should not be treated merely as a cost-cutting issue. "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 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," he said.

The UK government must now decide whether to fight Shell's corner under the Ospar process. The outcome of those talks, should they happen, will set a precedent for future UK decommissioning, which could have a far-reaching impact on the finances and activities of companies operating in the North Sea.

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