Report: Deficient risk assessment led to drill rig grounding

ANCHORAGE, Alaska — A federal agency says the grounding of a Royal Dutch Shell PLC mobile offshore drilling rig in 2012 was due to the company’s inadequate assessment of risk involved in a winter tow across the treacherous Gulf of Alaska.

The National Transportation Safety Board issued its ruling Thursday on the Kulluk, which had been used to drill in the Beaufort Sea off Alaska’s north coast.

Shell later towed it to Dutch Harbor in the Aleutian Islands and attempted a gulf crossing to Seattle. The conical drill barge broke loose from its tow vessel seven days into the transit.

Reattached lines failed in stormy seas, and the Kulluk ran aground.

Spokesman Curtis Smith says Shell is reviewing the NTSB report but has already incorporated lessons learned.

Shell intends to resume Arctic offshore drilling operations this year.