A drilling vessel aground off a remote Gulf of Alaska island is upright and stable, but has suffered damage to generators and its upper deck.
Royal Dutch Shell incident commander Sean Churchfield said a salvage team found open hatches that allowed water to enter the Kulluk, which drilled in the Beaufort Sea during the 2012 open water season.
The US Coast Guard said there was no indication of a fuel leak.
The drilling barge ran around on Monday night after it lost a line to its main towing vessel and could not be controlled by a tugboat.
Mr Churchfield said damage to the barge's generators meant salvagers might have to bring external generators on board or work without power. He said the salvage was in the assessment stage and it was too early to tell when the vessel could be moved.
Meanwhile, calls for US government scrutiny of Royal Dutch Shell drilling operations in Arctic waters grew with a request for a formal investigation by members of Congress.
The House of Representatives' Sustainable Energy and Environment Coalition called on the Interior Department and the coastguard to jointly investigate the New Year's Eve grounding of the Kulluk and a previous incident connected to Arctic offshore drilling operations last year.
"The recent grounding of Shell's Kulluk oil rig amplifies the risks of drilling in the Arctic," the coalition's 45 House Democrat members said in a joint statement. "This is the latest in a series of alarming blunders, including the near-grounding of another of Shell's Arctic drilling rigs, the 47-year-old Noble Discoverer, in Dutch Harbour and the failure of its blow-out containment dome, the Arctic Challenger, in lake-like conditions."
The coalition believed these "serious incidents" warranted thorough investigation, the statement said.
Shell Alaska spokesman Curtis Smith said the company supported and was providing resources for the investigation of the grounding by the Unified Incident Command, made up of government, state and company representatives. Mr Smith said the findings would be available to the public.