Royal Dutch Shell has abandoned a contentious Arctic drilling campaign off the coast of Alaska and is preparing to take billions of dollars in writedowns after its exploration efforts failed to make a significant discovery. The decision, likely to be welcomed by environmental campaigners, reflected the high costs of the project and the “unpredictable” US regulatory environment, Shell said. The collapse in oil prices since last June, from more than $115 a barrel to less than $50 now, has called into question the viability of challenging, high-cost production in areas such as the Arctic. Dozens of projects have already been put on hold. Shell, when it embarked on its summer drilling campaign in the Chukchi Sea, had said that the time and expense were justified by the size of the prize if exploration was successful. Its Burger prospect is in an area that has been estimated by the US as potentially holding 4.3bn barrels of recoverable oil.