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NTSB faults Shell for Kulluk grounding Agency says company did not adequately assess the risks involved in the winter tow of the drilling vessel around the Gulf of Alaska Alan Bailey Petroleum News
The National Transportation Safety Board has published the results of its investigation into the December 2012 grounding of Shell’s Kulluk floating drilling rig and has blamed Shell’s inadequate risk assessment for the accident.
“The series of failures that led to this accident began when Shell failed to fully address the risks associated with a late December tow in Alaska waters and ended with the grounding of the Kulluk,” the NTSB report says. “Although multiple parties were involved in the review and approval of the tow plan, the ultimate decision to approve and implement the plan was Shell’s.”
Research into catastrophic events has demonstrated that, in a situation where a single party favoring a particular decision has ultimate decision-making authority, multiple parties involved in the ill-fated operation have limited ability to draw attention to risks, the report says.
Grounded during gale The Kulluk ran aground on the eastern coast of Sitkalidak Island off Kodiak Island on Dec. 31, 2012, in a severe gale. Shell had been attempting use the Aiviq, an anchor-handling tow supply vessel, to tow the drilling rig from Dutch Harbor in the Aleutian Islands to the Seattle, Washington, area for winter maintenance. The grounding followed a series of incidents including the parting of the towline between the rig and the Aiviq in heavy seas and the loss of the Aiviq’s engine power. The Kulluk had been participating in Shell’s summer 2012 exploration drilling program in the Beaufort Sea. As a consequence of damage sustained during the grounding, Shell eventually had to scrap the Kulluk. However, the grounding did not cause any environmental damage, the NTSB report says. Four Aiviq crew members sustained minor injuries, the report says.
Shell had planned to move the Kulluk to the Seattle area, where the shipyard capabilities were more suitable than those in Alaska for the required maintenance. There was also a question of a possible liability of several million dollars in state property taxes, had the Kulluk remained in Alaska beyond the end of the year, the NTSB report says.
Coastal route Shell opted for a coastal tow route around the Gulf of Alaska, rather than crossing the center of the gulf, to allow easier access for search and rescue operations, should a problem arise. The tow plan, which took into account historical climate data for the route and season, was reviewed by several managers and a warranty surveyor before being approved by Shell’s Alaska operations manager, the report says. A warranty surveyor also inspected the Aiviq and the tow gear before the tow commenced.
Weather forecasts commissioned by Shell for the route predicted rough weather. But, according to Shell’s manager on board the Kulluk, the crew on the vessel had not anticipated seas as heavy as were actually experienced.
However, according to a Coast Guard investigation of the Kulluk grounding, a weather study had pointed to the possibility of winds and seas that would have exceeded the Aiviq’s towing capabilities, the NTSB report says.
Alarm activated On the day the towline actually failed in 15- to 20-knot winds and 20- to 25-foot seas, the tow system alarm had activated 38 times, with each activation indicating that the tow load had exceeded 50 percent of the 600-ton breaking strain of the tow wire, the NTSB report says.
Although after the towline breakage the Aiviq succeeded in connecting an emergency towline to the Kulluk, all four of the Aiviq’s engines failed, apparently because of fuel contamination. Although Offshore Service Vessels, the operator of the Aiviq, claimed that the fuel that the vessel had loaded in Dutch Harbor had been contaminated, Coast Guard investigators said that they believed that a faulty fuel storage tank vent and overflow design had led to seawater contamination. Offshore Service Vessels had to fly replacement fuel injectors from the Lower 48, to enable the Aiviq’s crew to restart the engines.
The eventual grounding of the Kulluk followed multiple attempts at towing the drilling rig by several vessels. Those vessels included the Aiviq and Shell’s oil spill response vessel, the Nanuq, as well as two tugs, the Guardsman and the Alert. Ultimately, the wind strength overpowered the towing operation.
Plan shortcomings “No single error or mechanical failure led to this accident,” the NTSB report says. “Rather, shortcomings in the design of a plan with an insufficient margin of safety allowed this accident to take place. The plan was created to move the MODU (mobile offshore drilling unit) at a time of year with a known likelihood of severe weather conditions for reasons unrelated to operational safety.”
Given the risks associated with the transit of the Gulf of Alaska, including the likelihood of severe weather, Shell and its contractors should have either mitigated those risks or conducted the tow at a time of year when the weather would have been more favorable, the report says. In particular, the deployment of additional tow vessels for the transit would have reduced the risks associated with a failure of the Aiviq or its tow gear, the report says.
“Redundancy is a necessary element of safety-critical transportation systems, and given the hazards of operations in Alaskan waters, those involved in the tow plan should have recognized and addressed the lack of redundancy,” the report says.
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