Although preliminary work began Sunday on an exploratory drill 70 miles off the coast of Alaska , a giant block of floating ice was delaying any further work from continuing.

A Royal Dutch Shell petroleum drill ship had begun the first drilling in U.S. Chukchi waters since 1991 but was forced to stop after only hours and move away to wait for an ice shelf 30 miles long, 12 miles wide and up to 82 feet thick to pass. A Shell Alaska spokesman said that could potentially take days. The Noble Discoverer moved 30 miles south until the ice pack passes and is unlikely to return.

Environmental groups say the interruption is indicative of the dangers in that region and underlines their challenges to Arctic offshore drilling. Shell spent $2.1 billion on Chukchi Sea leases in 2008 alone, and more than $4.5 billion in Arctic offshore drilling overall.

It is estimated that Arctic waters contain 26 billion barrels of recoverable oil and 130 trillion cubic feet of natural gas, which the state of Alaska hopes will help refill the trans-Alaska pipeline. The pipeline now runs at less than one-third capacity.

The offshore injury lawyers of Schechter, Shaffer & Harris, L.L.P., Accident & Injury Lawyers know that offshore drilling can be one of the most dangerous working environments.