Faced with iced-in Arctic waters and failure to secure U.S. Coast Guard approval of its oil-spill barge, Royal Dutch Shell* is ratcheting down its plan to drill as many as five exploratory wells this summer in the seas north of Alaska.

The company planned to sink the wells in the Chukchi and Beaufort seas during a brief window between July and October, when the waters were expected to be clear of severe ice. But Pete Slaiby, Shell’s vice president for Alaska operations, said it’s unlikely the company will be able to meet that goal due to regulatory challenges and stubborn ice.

“We are still hopeful that we will get some wells drilled,” Slaiby said. “Considering what we’ve been through . . .