WASHINGTON — Federal investigators blamed the wreck of Shell's Kulluk drilling rig on the company's "inadequate assessment of the risk" when it was towed across stormy seas in 2012.
The National Transportation Safety Board reviewed the five-day fight to control the Kulluk before it careened into an Alaskan island. The board's conclusions could heighten scrutiny of Shell Oil Co.'s plans to resume exploratory drilling in the Chukchi Sea later this summer.
"Shortcomings in the design of a plan with an insufficient margin of safety allowed this accident to take place," the NTSB said in a report released Thursday. "The plan was created to move the (drilling unit) at a time of year with a known likelihood of severe weather conditions for reasons unrelated to operational safety."
The NTSB's report dovetails with the conclusions of a Coast Guard investigation that said financial considerations - specifically a potential multi-million dollar tax bill from Alaska - influenced Shell's timing.
Shell has since replaced the damaged Kulluk with the Transocean Polar Pioneer.
The Interior Department's Bureau of Ocean Energy Management has already approved the company's broad plans for drilling during ice-free waters this summer and in 2016. But Shell is waiting on drilling permits and other authorizations.
On Thursday, President Barack Obama defended the administration's posture on Arctic drilling, insisting during an online Twitter chat that regulators are "serious" about scrutinizing Shell's plans.
"We've shut off drilling in the most sensitive Arctic areas, including Bristol Bay," he said, "but since we can't prevent oil exploration completely in (the) region, we're setting the highest possible standards."
Separately, Interior Department officials began poring over thousands of public comments on their proposal for first-of-their-kind offshore drilling mandates specifically targeting Arctic operations. Oil companies and industry trade groups criticized a proposed requirement that firms have both rigs and time to drill relief wells in case of emergencies at their Arctic projects.
The botched towing of the Kulluk illustrates the difficulty of Arctic drilling endeavors, even though it actually came two months after Shell finished boring the top portions of wells in the Beaufort and Chukchi seas.
Shell contractor Edison Chouest began using its anchor handling vessel, the Aiviq, to tow the Kulluk from Dutch Harbor, Alaska to a Seattle shipyard Dec. 21, 2012.
But six days later, when the vessels ran into a series of storms near Kodiak Island, the tow line broke and Aiviq's four engines failed. The Coast Guard tried to establish a new tow line with the Kulluk, evacuated most of the rig's crew and delivered spare parts to the Aiviq, allowing some of its engine power to be restored.
Towlines were briefly reconnected between the Kulluk and the Aiviq as well as another tugboat, the Alert, on Dec. 31. But once the connection to the Aiviq failed, officials instructed the struggling Alert to release its line for safety reasons.
That sealed the Kulluk's fate.
Roughly a half hour later, at 8:48 p.m. on Dec. 31, the rig plowed into the rocky seabed on Alaska's uninhabited Sitkalidak Island.
Shell's executive vice president for the Arctic, Ann Pickard, insists the company has radically improved its oversight of its contractors in Alaska, with daily phone calls to share lessons learned, a down-to-the-minute operations plan outlining planned vessel movements, and more Shell managers overseeing individual contractors.
Pickard said "you can't compare" the level of planning in 2012 "to where we are today," because there have been so many changes.
At the time, Pickard said, the focus was on getting in to the Chukchi and Beaufort seas to drill during what remained of the brief ice-free window. As a result, Pickard said, the company planned "decently" going forward into the drilling operations, but "it wasn't decently planned coming out."
Shell spokesman Curtis Smith said Thursday that the company was reviewing the National Transportation Safety Board report.
"We will continue to test and prepare our personnel, assets and contingency plans against the high bar stakeholders and regulators expect of an Arctic operator," Smith said.
Environmentalists say they have no way to independently assess Shell's operations - including how much the company learned from mishaps in 2012. An independent audit of the company's management systems - ordered by the Interior Department in 2013 - has not been publicly released to Greenpeace and other groups that have requested it under the Freedom of Information Act.