The Kulluk's troubles started on Dec. 27, when a tow shackle between the drilling rig and its tug, Shell's Aiviq, failed. A second towline was attached, but later the engines on the Aiviq failed, leaving the two vessels adrift at sea. The 266-foot diameter Kulluk has no propulsion system of its own.

Over the next several days, more tugs were called in from across Alaska, but all struggled to hold on to the drifting Kulluk. By Monday, rough seas and more problems forced a tug crew to let go of the Kulluk, sending it drifting into the rocky shoreline of Sitkalidak Island.

More: Did Alaska tax liability play role in Kulluk's mad dash south?

Concerns have turned to protecting the area's salmon streams and sea lion and seal rookeries from contamination in the event the Kulluk begins to leak.

Shell has invested more than $5 billion since the mid-2000s in a quest to reignite a controversial Arctic drilling program that it started in the 1980s. The Kulluk was one week into a three- to four-week journey from the busy Aleutian port of Dutch Harbor to Washington state, where the rig was expected to undergo routine maintenance in an effort to prepare for the 2013 drilling season.

Full story: Fuel tanks of grounded oil rig pointed out to Gulf of Alaska