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Watching for the ice in the Chukchi
Modern satellite-based synthetic aperture radar technology is enabling the detection of sea ice in the dark and in cloudy conditions, thus greatly improving ice observation capabilities for ice management during Arctic offshore oil and gas exploration, Peter Noble of ConocoPhillips told the U.S. Minerals Management Service Arctic Technologies Workshop in Anchorage on Oct. 14.
By reflecting radar signals off the ice, synthetic aperture radar can produce images over a range of scales, and in great detail.
“We can take pictures of a 500-km square all the way down to a 20-km square at any time,” Noble said. “… We use different scales for different reasons as we develop our plots.”
In fact, during the summer of 2009 ConocoPhillips was able to detect a 240-foot survey boat on the water using a Chukchi Sea radar image, he said.
Ice management zones During a drilling operation, sea-ice management would be based on the delineation of concentric zones around the drillship. The observation of ice entering a specific zone would trigger ice management activities, breaking up the ice and moving it out of the way. If the threat persists drilling operations would be suspended. And depending on circumstances, such as the ice entering a critical zone close to the drillship, the well might have to be secured and the drillship moved from the site.
The timing of any decisions on ceasing drilling would depend on a defined “time to react,” a time that varies depending on the status of the drilling operation, but which tends to increase as the drill bit penetrates further into the subsurface.
Chukchi drilling ConocoPhillips is planning to drill an exploration well in its Chukchi Sea Devil’s Paw prospect, in the vicinity of the old Klondike well, in the open water season of 2011, at a time when sea ice is very unlikely to present a problem at the drill site, Noble said.
In fact, the company has been assessing past Chukchi Sea ice conditions, to determine when the drilling would best be carried out, he said. An analysis of past ice cover indicates a slow increase in the open water season length over the years, but the year-to-year variability in the ice-cover timing tends to obscure that trend towards a longer season.
Historical ice-cover data suggests a likely drilling season of up to 100 days at the planned drilling site. There has always been ice cover at the site in June, but the ice starts to retreat in July, with a 90 percent probability of the site being clear of ice by the end of August, Noble said.
—Alan Bailey
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