Shell has a very short time frame to start energy exploration work in the arctic waters off the coast of Alaska, an energy expert said. Shell\'s operational fleet is docked at Dutch Harbor, Alaska, as it waits for sea ice to clear. The regional conditions mean Shell needs to finish work in the Chukchi and Beaufort Seas by October to avoid reforming ice sheets. Tad Patzek, a professor of petroleum engineering at the University of Texas at Austin, said if Shell gets its rigs in position by mid-August, it could \"at best\" get three wells drilled this year. \"They should have started drilling by now because their window of opportunity is very short,\" he told Bloomberg News. Environmental groups pounced when Shell this month said its Noble Discoverer drillship slipped anchor in Dutch Harbor. They say operations could jeopardize the pristine arctic environment. Shell said the drillship didn\'t run aground and no injuries and no pollution were reported in the incident. The company estimates that there may be as much as 25 billion barrels of oil in the region. Shell spokeswoman Kelly op de Weegh told Bloomberg the company was committed to environmental protection. \"We remain confident we are setting a very high bar in the Arctic,\" she said.