The benchmark crude grades of the Middle East have slumped this week as the U.S.-Iran deal raises hopes that supply from the top oil-exporting region would begin to recover soon. As a result of the eased concerns about prompt crude supply from the region, the key benchmark crudes, Dubai and Murban, saw their futures curve structure on Tuesday flip to contango for the first time since the war began on February 28, according to data compiled by Bloomberg. The contango structure, in which prices for contracts dated further out in time…