"The barriers and contingencies we have in place and the significantly different characteristics of the wells we plan to drill here gives us tremendous confidence that the chances of a similar event taking place in the Alaska offshore is extremely remote," said Curtis, the Shell spokesman.
In the "extremely unlikely" event of a blowout or spill, Shell would be ready to respond in one hour with an "unprecedented" three-tier system consisting of an on-site oil spill response fleet, near-shore barges and additional vessels and response teams staged across the North Slope, company officials said.
The company is required to be able to handle a blowout of 5,500 barrels per day, about the size of the Gulf of Mexico release.
The Minerals Management Service estimates there is a 40% chance of a major oil spill of 1,000 gallons or more once drilling commences in the Chukchi Sea. But, as happened with the Deepwater Horizon lease, the agency calculated that the chances of a full blowout were so minuscule that it elected not to do a full study of what the environmental consequences of such a disaster would be.
Company officials said they have also conducted multiple independent inspections of the blowout preventer, a device whose apparent failure may have led to the Deepwater Horizon accident, to assure it could not experience a similar failure.
The exploration program is scheduled to take place in the relatively ice-free summer months, but oil spills under icy conditions raise a new level of complexity: how to track and control oil trapped under ice, how to gather oil that is seeping through melting ice, how to move vessels and containment booms through closely clustered ice floes.
Cleanup under these conditions could take months, some scientists studying the problem predict, in a harsh, fragile environment where rejuvenation milestones may be measured in decades, not years.
"If a spill were to happen off the coast of the North Slope, maybe 500 miles or so in broken or light ice conditions, it could realistically be days or weeks before anyone could even get to the source of the spill," said Joe Cunningham, research engineer with the NOAA-funded Coastal Response Research Center in New Hampshire.
"The other problem is since the Arctic is such a new environment for oil spill operations, we're kind of relying on equipment that was developed for warm water use. There hasn't been a lot of study done on how that same equipment will operate under Arctic conditions."
Recent industry-backed studies in Norway have suggested that low Arctic temperatures could actually help in spill cleanups. "Ice is a blessing and a curse," said Ron Morris, general manager of Clean Alaska Seas, an industry co-op that handles spill cleanup on the North Slope. "It's hard to get around in it, but it also doesn't allow the oil to expand; it keeps it kind of like a boom, captured, and it keeps the oil layer thicker."
Times staff writer Christi Parsons in Washington contributed to this report.