ANCHORAGE, Alaska — Hours after a repaired Shell icebreaker eased past protesters in Oregon to join an Arctic drilling operation, the oil giant used other vessels in its flotilla to begin excavating off the coast of Alaska in hopes of confirming the presence of billions of barrels of crude below the ocean floor.

Royal Dutch Shell PLC now only needs the 380-foot Fennica, repaired at a Portland shipyard, to be on hand at the drill site to ask federal regulators for permission to dig into oil-bearing rock already included on its Arctic offshore leases.

The drilling would come over the protests of environmental groups in Portland and elsewhere who say Shell has not proved it can clean up a major spill.

Critics have decried Arctic offshore drilling since before the federal government auctioned off billions of dollars in leases to Shell and other companies in 2008.