Arctic conditions at sea pose special challenges in gathering seismic exploration data – and ice in the water, while a big problem, isn’t the only obstacle.
There’s the wind.
There’s the low-lying ice.
There’s the environment.
There’s the local population.
And perhaps mainly, you can add to the list the challenge of simply protecting the new technology and equipment needed for 3-D seismic surveys, which can be especially at risk.
“It’s very difficult to protect the equipment, so ice avoidance is the best strategy,” said David Lippett, geophysical adviser for Arctic veteran Petroleum Geo-Services.
That’s not as easy as it might seem.
Even in so-called “ice-free” waters in summer months, icebergs, bergy bits, growlers and drift ice threaten ships and seismic arrays.
The summer season in the area between Greenland and Canada typically lasts from June to October, so gathering as much data as possible in a limited time is important. Careful planning to avoid known areas of ice must be routine.
Smaller equipment spreads of six to eight streamers are easier to protect by steering around ice. Using 10 to 14 streamers helps pull in more data in less time, but a 3-D equipment spread being towed can stretch a kilometer wide and several kilometers in length, Lippett said.
Larger spreads may offset the risk of damage by taking less time, he added.
Growlers and bergy bits – chunks from larger icebergs – usually float low in the water, weigh several tons and may be 90 percent below the surface. They are difficult to spot visually or with radar.
And even when the ship steers around the obstacles, the ice can still wreak havoc on the towed equipment.
“We constantly look at ways to adapt our equipment,” Lippett said, “or new ways to gather data.”
Pristine Environments
Equipment that can be towed at greater depths with new multi-sensor streamer technology is one method being used. At 15-20 meters deep, the streamers are below the growlers and drift ice.
Deep towing also allows a survey to continue during rougher weather, saving further time.
Ocean bottom nodes – single, remote units placed on the seabed without cable or other connections to the surface – “may be best for year around coverage,” Lippett said.
“The technology is out there, but ... it’s not straightforward, it’s slower,” he said, “and until the technology is more mature, it’s not as efficient as using streamers and hydrophones.”
Other technology needs to be explored as well, he said. Specialized radar for detecting low-lying ice needs to be refined more, he said.
Vessels must be fit for arctic conditions.
“The remoteness means you must be very self-sufficient for the health and safety of the crew,” he said.
Ice is only one challenge.
“We’re working in pristine environments, and seismic can have an impact on marine mammals and the environment,” Lippett said.
Working responsibly with local communities that might be affected also is important.
Narwhales are a highly protected species, and in some areas there are people who traditionally hunt the mammals for subsistence.
Hence, exploration surveys must be planned to avoid disrupting breeding patterns and displacement of the animals, Lippett said.
“We don’t believe our sound sources have a serious impact, but we still have to comply with permitting regulations,” he said. “We try to develop sound sources that are as efficient as possible, with no unnecessary disruption.”