Shell oil company will send a damaged ship carrying equipment required for Arctic offshore oil drilling from Alaska back to the West Coast for repairs.

Royal Dutch Shell PLC 's drilling schedule for two exploratory wells this summer in the Chukchi Sea off Alaska's northwest coast, however, shouldn't be delayed by maintenance work on the 380-foot icebreaker Fennica, spokesman Curtis Smith said Monday.

"We do not anticipate any impact to the (drilling) season as we do not require the vessel until August," Smith said.

The Fennica's primary job for Shell is carrying equipment for stopping an underwater well blowout.

Shell and other companies hope to tap into one of the country's last great petroleum reserves. The U.S. Geological Survey estimates the Arctic offshore reserves in the Chukchi and Beaufort seas at 26 billion barrels of recoverable oil.

Shell has invested upward of $7 billion on leases and exploration expenses.

Arctic offshore drilling is bitterly opposed by environmental groups that say major oil spills are inevitable in the inhospitable region that features brutal storms and sea ice most of the year. They say oil companies have not demonstrated they can clean up a spill in ice and that burning petroleum from the region will accelerate global warming and melt sea ice.

The hull of the Fennica was gashed July 3 as it departed Dutch Harbor in the Aleutians for the Chukchi Sea. The vessel under the direction of an Alaska harbor pilot struck an uncharted object, creating a hole in the hull about 3 feet long and a half-inch wide.

The National Oceanic and Atmospheric Administration announced Monday its mapping ship Fairweather had found shallow, rocky areas near where the hull was damaged.

The agency submitted a "Dangers to Navigation Report" to the Coast Guard listing the shoal depths, which are less than 30-feet deep in sections.

The Fennica carries a capping stack, the third line of defense in what Shell says is an unlikely scenario of a blowout. A capping stack is a roughly 30-foot device that can connect to a well head and stop gushing oil.

The icebreaking ship could also be used to manage icebergs near drilling vessels.

Shell said the special steel in the Fennica's hull meant a permanent fix would be required in dry dock. "While we believe the interim repairs could have been made in Dutch Harbor, our preference is to pursue a conservative course into a shipyard where a permanent fix can be performed," Smith said.

The Coast Guard has approved a plan for temporary repairs in Dutch Harbor that will begin soon, Smith said. The Fennica made the trip from Portland to Dutch Harbor in about two weeks. The return trip will depend on weather.

"There's no specific timeline," Smith said. "We just want to make sure it's a safe journey."

Shell hopes to begin exploratory well work as early as next week, but is awaiting final permits to drill from the federal Bureau of Safety and Environmental Enforcement.

Shell's two drill vessels remain in Dutch Harbor. Three other vessels from the 30-ship flotilla have left for Arctic waters, Smith said.