

An oil well suffers a blowout, causing a fatal explosion on an offshore platform. Oil spews into the water at an estimated rate of 53,000 barrels a day.

Company executives and government officials blame each other as they try to find a way to stop the flow of oil.

The Deepwater Horizon disaster of 2010 was a tragedy in many respects, but in one detail, BP — the operator of the well, which is now facing a bill of as much as $50 billion — was lucky. At least it could find the oil.

As more and more companies venture into the oil- and gas-rich waters north of the Arctic Circle, they are being forced to imagine another oil-spill scenario, one in which the response effort is impeded by storms, fog, high winds and massive drifting ice floes; in which visibility is minimal, where the nearest coast guard station is over 1,000 miles away and where spilled oil accumulates on, in and under the ice.

Such considerations have led to the development of new technologies to detect and deal with spilled oil in remote, icy seas.

In "open water" conditions such as those in the Gulf of Mexico during the Deepwater Horizon spill, the primary method for oil-spill detection involves satellite-mounted synthetic-aperture radar (SAR). This technology, which can see through clouds and in the dark, involves bouncing radio waves from orbiting satellites off the surface of the sea.

Any oil floating on the surface has the effect of smoothing the waves made by the wind on the water. Admittedly, it is almost impossible to tell the difference between an oil slick and a patch of calm water. But at least clean-up teams have some idea of where to start more detailed searches.

In the Arctic, however, SAR is less useful. One problem is that floating ice looks just like oil or calm water to a SAR-equipped satellite. According to Rune Storvold of the Northern Research Institute, a Norwegian research outfit, SAR-based oil detection is only effective in conditions with less than 30% ice coverage.

Oil on the surface of the water, or sitting on top of snow or ice, can be detected from boats or planes using infra-red (IR) and ultraviolet (UV) scanners which can indicate both where, and how thick, the layer of oil is. Because oil and ice have different temperatures, heat signatures and reflective properties, combined IR-UV scanners can be used to differentiate between smooth water, ice and slicks.

They can also differentiate between thicker oil deposits, which reflect more sunlight and emit less heat, and thinner ones. This year Eni Norge, a subsidiary of Eni, an Italian oil giant, equipped its fleet of emergency vessels in the Barents Sea in the Norwegian Arctic with cameras made by Aptomar, a Norwegian company.

Such systems can spot oil on the surface of the water or on top of ice, but they need a clear line of sight to the oil in order to work. A spill in the Arctic is likely to result in oil under rather than on top of the ice. Even oil on the surface may quickly be covered by snow.

For such scenarios, the most promising detection technology is ground-penetrating radar (GPR), which uses high-frequency radar signals, emitted either from a sled on the surface of the ice or from a low-flying aircraft, to provide an image of the subsurface. Snow, ice and oil reflect radio waves in different ways, allowing oil spills to be seen beneath the surface.

Oil and water

GPR has been shown to be particularly effective in detecting oil under snow. In 2010 SINTEF, a Norwegian research organisation, carried out a controlled spill on Svalbard. A helicopter-mounted GPR system successfully differentiated between ice sheets that concealed oil and those that did not.

As with other imaging technologies, the real improvements in GPR in recent years have been in the software for making sense of the collected data, rather than in hardware, says David Dickins, project manager of the SINTEF experiment.

Even so, GPR has its limitations. "Sea ice is very inhomogeneous — it's not like a flat slab," says Dr Storvold. Ridges, hollows, and variation in thickness can all deform or scatter the GPR signal, making the picture less clear and oil spills harder to spot. The situation is further complicated by the presence of salt, which absorbs the radar signals, weakening the reflection.

Earlier this year America's Bureau of Safety and Environmental Enforcement, with support from ExxonMobil, Shell, Statoil and other oil giants, conducted an experiment with high-power radar to try to improve the range of conditions in which GPR would be effective.

The high-power system showed some improvements compared with previous tests: it was, for example, able to profile the shape of the underside of the ice. But the test also highlighted the limitations of GPR, particularly in conditions when the ice is close to melting.

To get a more accurate picture of oil under the ice layer, several companies are working on detection systems based on nuclear magnetic resonance (NMR). This technique, widely used in medical scanners, relies on variations in the magnetic properties of the nuclei of different elements.

A carefully tuned electromagnetic pulse causes the nuclei to flip over, and as they right themselves, they emit radio signals — a phenomenon called nuclear magnetic resonance. The strength of these signals can be used to differentiate different materials. Crucially, ice is transparent to NMR, which means it cannot be misled, as GPR can be, by odd-shaped ice formations.

Last year America's patent office published details of an application from several scientists from Upstream Research Company, a division of ExxonMobil, in which they claimed that NMR techniques "provide a solution to a need for oil-spill response in ice-prone environments that has existed for over 30 years". Shell, which has spent billions of dollars preparing to look for oil off the coast of Alaska, also says it is working on NMR to detect oil spills.

NMR has its drawbacks, however. As with some GPR systems, NMR systems are carried by helicopter. But the large, ring-shaped antenna required is much larger than that required for GPR. According to Steve Potter at SL Ross, a consultancy, the diameter of the ring must be roughly equal to the distance of the antenna from the oil.

To detect oil trapped beneath two metres of ice, the helicopter must hold the ring just three metres above the surface. That is no easy feat in calm conditions, let alone a blizzard. And NMR cannot determine the thickness of oil — which, says Mr Potter, is "still a bit of a holy grail issue".

The newest approach to detecting oil under ice approaches the problem from another angle: underwater. It relies on a combination of two existing oceanographic technologies: robot submarines, known as autonomous underwater vehicles (AUVs), and sonar.

Unlike remotely operated underwater vehicles, which must be tethered to a control system on a boat and are therefore limited to a range of several hundred metres, AUVs can be programmed to rove beneath the ice over distances of several kilometres.

Submarine dream

In tests carried out earlier this year at the Cold Regions Research Engineering Laboratory in New Hampshire, researchers from the Scottish Association for Marine Science equipped AUVs with a suite of sensors, including multi-beam sonar.

Once under the ice, the AUV fired pulses of sound upwards. Ice and oil reflect the sound waves back again in different ways, allowing the presence of oil to be mapped. The thickness of the oil layer could be measured to within millimetres, says Jeremy Wilkinson, who led the project.

Combining multiple detection systems, including cameras, sonar and lasers, could improve accuracy and reliability. "It may not be the silver bullet, but at least we have a package that can work in conditions where other technologies struggle," he says.

Although the technologies for detecting and mapping spilled oil in icy waters are rapidly improving, the options for cleaning it up remain limited. In open water, there are two main methods for dealing with spilled oil. The first is to hem it in with booms and then either skim it off the surface or burn it. The second is to apply chemical dispersants to break the oil down into droplets that can be more easily digested by naturally occurring bacteria.

For oil spilled in the Arctic, ice can act as a natural boom that prevents the oil from spreading out over vast distances, as happens in open-water spills. And at colder temperatures, oil is more viscous and diffuses less quickly. Lower temperatures also expand the window of time during which the surface oil can be burned off. In warm-water spills the lighter, flammable fractions of the oil evaporate within hours.

But whatever advantages the Arctic offers for oil-spill response, they are overwhelmingly outweighed by the difficulty of access. Even in the Deepwater Horizon spill, only 3% of the oil was skimmed, according to America's National Oceanic and Atmospheric Administration. Burning is not an option for oil trapped under ice. That leaves only dispersants.

Kenneth Lee, the director of Canada's Centre for Offshore Gas and Energy Research, says genomic research suggests that naturally occurring bacteria may be able to break down a lot more oil in cold water than was previously thought. His team is working on special cold-water dispersants to accelerate this natural process. But given the difficulty of mounting a clean-up operation in Arctic conditions, the industry's focus is likely to remain on developing detection technologies that spot problems quickly — and doing everything possible to prevent spills from happening in the first place.

"The ability to detect oil in icy water is improving, but the options for cleaning it up remain limited."

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