Shale output in the United States will prove resilient to low oil prices likely to be prolonged by the prospect of half a million barrels per day of Iranian crude making its way back to the market, BP’s chief economist said on Tuesday. Talks in Vienna between world powers trying to end sanctions on Tehran in return for limits on Iran’s most sensitive nuclear activities could bring a significant increase in Iranian oil exports. BP’s Spencer Dale, however, told Reuters that it would probably take time for any easing of sanctions to filter through to oil markets if an Iran deal is agreed. His “hunch” was that the outcome of the talks would be closer to U.S. demands that restrictions should be eased after a period of monitoring rather than the rapid change sought by Iran. U.S. and European Union sanctions ban their companies from buying Iranian oil. […]