The U.S. arm of Royal Dutch Shell, which is being scrutinized over its plans to explore for natural gas and oil offshore Alaska, pledged last week to deploy a prefabricated coffer dam ready for "immediate" use in the event of a well blowout and to launch a full-scale oil spill response within an hour.

Shell Oil Co. President Marvin E. Odum sent a letter last Monday to Minerals Management Service (MMS) Director S. Elizabeth Birnbaum to reassure federal officials that offshore drilling in the Chukchi and Beaufort seas could -- and would -- be safely conducted.

Birnbaum early this month asked Shell for guidance as to what additional safety measures it would implement at the Alaska drilling sites in light of the tragic Gulf of Mexico (GOM) oil spill (see related story). A spill in the remote Alaska seas could wreak havoc on the Arctic's ecosystem, according to officials.

"Shell is committed to undertaking a safe and environmentally responsible exploration program in the Chukchi Sea and Beaufort Sea in 2010," Odum said. "I am confident that we are ready to conduct the program safely, and, I want to be clear, the accountability for this program rests with Shell."

At the ready would be dispersant that could be used underwater near any source of oil flow. A remotely operated submersible and trained divers also would be stationed at the drilling site, said Odum.

The coffer dam built for the Shell site would "take into consideration" the problems experienced by BP plc in its response to the GOM oil spill, Odum said. In one of its attempts to control the flow of oil from the Macondo well in the GOM deepwater, BP deployed a 100-ton containment dome over one of the riser leaks, but the plan was abandoned after it became clogged with crystallized methane gas.

Shell would rely on a fleet of response vessels that would accompany the drilling rig and other equipment that would be stationed in Wainwright, AK, and elsewhere on the North Slope, Odum said.

In the letter Odum also emphasized that the chances of a blowout would be much lower than at the BP spill in the GOM, which occurred in water almost a mile deep. The BP well encountered pressures two to three times more than Shell expects in Alaska, where drilling would be done in about 150 feet of water.

Shell also has enhanced its blow-out prevention (BOP) equipment, which apparently failed at the BP spill, said Odum. Shell's devices would be tested weekly instead of every 14 days -- as originally proposed -- and the BOPs could be manually operated if necessary.

In addition, Shell is evaluating a backup set of "shear rams," knife-like devices that would be used as a last resort to regain pressure in a well by cutting and sealing drill pipe.

Alaska's congressional delegation is in favor of Shell moving forward with its offshore drilling plans.

Democratic Sen. Mark Begich said last week Shell has responded adequately to the MMS request for information.

"It's an effort to show that we can do this development the right way up here," Begich said. "We've done it. We've worked in extreme conditions and have had OCS [Outer Continental Shelf] development."

Alaska's Republican Sen. Lisa Murkowski said, "Just because it's difficult doesn't mean we pull back in any way."

To date there has been no major commercial oil and gas production from U.S. offshore territory in Alaska, and the state would not receive royalties or tax revenue from Shell's offshore wells. BP is the only producer now developing an offshore oil operation.

However, Shell's emergency response plans for drilling incidents offshore Alaska still appear to be insufficient, according to the Pew Environment Group's Arctic Program, an arm of the Pew Charitable Trusts.

Even though Shell has stated that a blowout like the disastrous one in the GOM would be unlikely because such incidents are "extremely rate" in shallow water, Pew's Marilyn Heiman noted that a 2007 MMS study found 19 of 39 offshore blowouts between 1992 and 2006 were in water less than 200 feet deep.

"Basic questions remain about Shell's ability to respond to any significant sized oil spill in Arctic waters," Heiman said. "MMS should suspend offshore lease operations in the Arctic until these issues are addressed. It would be irresponsible to move forward."

The risks were evaluated before the leases were sold, said Jason Brune, executive director of Resource Development Council for Alaska. Postponing Shell's exploratory program would be a "huge setback for the Alaskan economy," he said.

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