One of the world’s largest areas of offshore oil and gas exploitation, in Europe’s North Sea, is closing down. Over the next few years, thousands of wells will be plugged and hundreds of giant production platforms removed from the storm-tossed sea, in one of the world’s largest and most expensive exercises in industrial decommissioning.
Good riddance? Three cheers for the cleanup? Not so fast. Some ecologists are pleading for the rigs to be left behind, at least in part, to support the marine life that has grown up around them. And they fear the dismantling could disturb toxic drilling waste on the seabed that nobody plans to remove.
How this plays out could yield important lessons for the decommissioning of other offshore oilfields from the coasts of California and Brazil to the South China Sea and, potentially, the Arctic.
Two decades ago, the North Sea was one of the world’s largest sources of oil, pumping up 6 million barrels a day. That figure is now down to 1.5 million barrels, and the industry is turning to the task of decommissioning the estimated 600 production platforms in the North Sea. The British sector alone contains 470 of them, along with roughly as many other offshore installations, plus 10,000 kilometers of pipelines and 5,000 wells. The British industry expects to carry out more than 200 decommissions between now and 2025.
Many steel rigs will be cut off just below the seabed, and either dragged ashore in one piece or dismantled offshore. A handful of early giant concrete structures, which can weigh as much as 400,000 tons, may have to stay put because there is no way of moving them.
The British industry estimates the final bill at $51 billion, though some analysts say it will be double that. Whatever the price, since decommissioning is tax deductible, the cost will be largely born by taxpayers. Are they getting value for their cleanup cash? Will the expenditure even be good for the environment? Some ecologists say no on both counts.
The issue of what to do with the rigs has been toxic since 1995, when oil giant Shell sought to move the Brent Spar, a floating oil storage facility, from the North Sea out into the Atlantic for dumping in deep water. A public outcry, led by Greenpeace, followed. Shell products were boycotted in several European countries, and there was even an arson attack on a filling station in Germany.
In the wake of that, OSPAR, an international treaty of 15 European nations that aims to protect the environment of the Northeast Atlantic, established new rules requiring almost all the industry’s infrastructure to be brought ashore when it was no longer needed, for reuse or recycling. The only exceptions were about 40 of the largest platforms, whose owners may apply for “derogations” to leave them in place.
Many of the rigs have turned into valuable habitats, acting as surrogate reefs that are often occupied by rare species.
The OSPAR rules initially looked like a victory for the marine environment. But there has been a growing debate among marine scientists about whether the cleanup may sometimes do more harm than good. For during their lives of 30-40 years, many of the rigs have turned into valuable marine habitats, providing rare hard structures in a sea whose bed is mostly soft sand and mud. They are surrogate reefs, often occupied by rare species.
Marine ecologist Lea-Anne Henry and colleagues from the University of Edinburgh have studied reef creatures such as cold-water corals, barnacles, mussels, and sea anemones at 66 North Sea platforms. They concluded that “platform ecosystems are evolving to mimic those in the wild.” A collaborative research project called INSITE (Influence of Man-made Structures In The Ecosystem) reported this year that some North Sea rigs act like “small offshore islands,” supporting marine communities that need hard surfaces and attracting predators such as fish, mammals and seabirds.
The evidence is growing that rigs can even play an important role in nurturing surrounding natural ecosystems. Linked by ocean currents and pipelines, they form a network of “stepping stones” between natural reefs for species such as cold-water corals made rare in the Atlantic by destructive trawling, says Henry. Marine life around the remains of the partially decommissioned Murchison and Thistle A platforms supply larvae of Lophelia pertusa, a rare cold-water coral, to the nearby Aktivneset marine protected area, which is famous for its coral.
This may not be unique. A number of other platforms are close to proposed conservation zones. The British gas company Centrica has a platform only 3 kilometers from an area known as Markham’s Triangle, where seals gather to eat sand eels. ConocoPhillips is currently decommissioning structures in its Viking gas field, where harbor porpoises and white-beaked dolphins are frequently seen.
It is often assumed that platforms pose a serious risk to such special habitats. But it is at least possible, that the platforms may sometimes help sustain them. “Some marine mammals are attracted to some man-made structures,” says Jonas Teilmann of Aarhus University in Denmark.
Further evidence of the potential long-term value of rigs in the North Sea and elsewhere comes from the marine wildlife often abundant around shipwrecks. For instance, recent surveys have highlighted a cornucopia of marine life among the 52 German warships that were scuttled in Scapa Flow off the Orkney islands in northern Scotland at the end of the First World War.
All this is confusing for environmental campaigners. Some groups take the approach that big oil has a responsibility to leave behind habitat that is as near to pristine as possible. Lyndsey Dodds of WWF UK says: “Having made hundreds of millions of pounds in profits over the past few decades, oil and gas companies operating in the North Sea have a legal, as well as a moral, obligation to clean up their mess.”
But others concede that things are not so simple. “By removing rigs, we risk losing rich biodiversity hotspots that have come to form an integral part of the wider ecosystem,” says Anne-Mette Jorgensen, founder of North Sea Futures, a non-profit organization that promotes ecosystem-supportive design and management of offshore structures.
Sam Collin, a marine scientist at the Scottish Wildlife Trust, takes a similar view about the potential environmental benefits of leaving rigs behind in the many oilfields off the Scottish coast. Decommissioning, Collin says, “creates a range of ecological disturbances: release of trapped chemicals, seafloor disturbance, increased sedimentation, and removal of an established marine community growing on the structure.” Once oil platforms are cleaned of pollutants, he notes, they are “essentially inert structures that can continue acting as reefs. Leaving them in place could have a net environmental benefit.”
Some green groups say the money the oil companies save by leaving rigs in place should go into marine conservation.
The continued presence of abandoned rigs could also provide protection from other threats. “Fishing is restricted up to 500 meters from oil platforms. These restricted zones make up approximately 1 percent of the North Sea area and could provide important refuges for fish,” says Collin. “Once the rig is removed, these marine communities disappear and fishing returns to the area.” For such reasons, a trust policy adopted in 2013 says that “the current presumption of complete removal of offshore infrastructure should be reconsidered.”
Neither Scottish Wildife Trust nor North Sea Futures want to let big oil off the hook, however. They say the money saved by leaving rigs in place should go into marine conservation rather than shareholders’ pockets. “It could free up as much as $10 billion that could be invested in restoration of natural reefs, or in other projects like more sustainable fishing or renewable energy,” says Jorgensen.
There are precedents for leaving rigs in place to attract marine life. A “rigs-to-reef” program adopted in the 1980s in U.S. waters of the Gulf of Mexico left the sub-surface remains of about 500 platforms, more than a tenth of the total that had been installed. It has reportedly had some success in encouraging marine life.
In California, which has 27 offshore platforms mostly dating from the 1960s and 1970s, there is strong opposition from environmentalists to the idea of leaving rigs in place. But some local conservation scientists who have dived to the rigs take a different line.
Milton Love, a research biologist at the University of California Santa Barbara and others titled their 2014 paper on the topic: “Oil platforms off California are among the most productive marine fish habitats globally.” The platforms, they explained, “have a high ratio of structural surface area to seafloor surface area, resulting in large amounts of habitat for juvenile and adult demersal fish.”
The debate continues. But there is another issue in the decommissioning of offshore oil infrastructure that is much less discussed: What should happen to the huge piles of contaminated drilling waste piled up on the seabed around many well fields. This is waste that oil companies and governments seem much more determined to leave in place.
Oil platforms routinely use fluids to lubricate their drills. These fluids are either oil- or water-based and contain metal additives, such as barium sulphate, that increase the density of the fluid and so help prevent well blowouts. After use, the fluids are brought back to the surface, mixed with fragments of rocks from beneath the seabed. Platform operators today attempt to extract and reuse the fluid. But until 2001, much of the remainder was simply poured onto the seabed.
Since then, such discharges have been banned by OSPAR. But the legacy of underwater slag heaps sometimes tens of meters high remains, smothering large areas of seabed, obliterating some ecosystems, and poisoning others. Industry surveys two decades ago estimated there was more than a million cubic meters of the stuff on the bed of the North Sea, covering 1,650 square kilometers.
Independent assessments of their ecological impact are rare. A 1995 study by John Gray of the University of Oslo found that they were killing organisms over areas up to 100 square kilometers around platforms. He reported “severe reductions in organisms that are key components of the benthic communities” and that “could potentially have negative effects on fish.” But concern has since subsided. In a recent paper, Henry found evidence that seabed communities have begun to recover in places.
One report concluded the environmental effects of trying to remove the waste would be greater than leaving it in place.
In the decade after Gray’s study, there were moves among some OSPAR member nations to have oil companies clean up all these wastes, by pumping them into tankers to be brought to land, injecting them into oil wells, or covering them with clean sand. But current OSPAR rules give wide exemptions that typically allow them to be left in place, says John Shepherd, former director of Britain’s National Oceanography Centre.
Shepherd chaired an independent review group that spent ten years examining Shell’s plans for decommissioning the giant Brent field in the North Sea. In 2017, the group signed off on the company’s plan to leave in situ cutting piles containing some 22,000 cubic meters of hydrocarbons, on the grounds that “although it is uncertain, the risk of environmental impacts… are not likely to extend beyond about 2-3 kilometers from the platforms.” In any case, his report said, the environmental effects of trying to remove the cuttings “would be likely to be greater than those of leaving the material in place.” But critics question how likely it is that the piles can remain undisturbed while tens of thousands of tons of equipment are being removed from the water above them.
”In practice, fully removing a platform, without removing the drill cutting pile, would spread pollution over a much larger area,” says Jorgensen. It might happen during decommissioning or subsequently, “when the area is opened up for trawlers,” she says.
The uncomfortable thought is that current decommissioning plans in the North Sea — by leaving the toxic cuttings piles while removing the metal rigs that have harbored marine life in profusion — could be the worst possible option for nature.