U.S. refiners will not be able to complete transactions for shipments of crude from Venezuela’s PDVSA for cargoes they had contracted before the U.S. Treasury slapped sweeping sanctions on the Venezuelan state oil firm, Bloomberg reports, quoting people familiar with the matter. Last Monday, the U.S. imposed sanctions on PDVSA to “help prevent further diverting of Venezuela’s assets by Maduro and preserve these assets for the people of Venezuela. The path to sanctions relief for PdVSA is through the expeditious transfer of control…