Russian state oil producer Rosneft will be forced to postpone drilling a second well in the Kara Sea for at least two more years, three sources told Reuters, as a result of Western sanctions over the Ukraine crisis. The delay will be a blow to Rosneft, which is key to President Vladimir Putin’s goal of lifting output and securing Russia’s energy dominance by exploring the Arctic, where Moscow is thought to have some of the world’s most plentiful oil resources. Rosneft, the world’s top listed oil firm by output, drilled a first exploration well known as Universitetskaya-1 last year in the Kara Sea, which is part of the Arctic Ocean, with the help of U.S. partner ExxonMobil which provided the rig.