HOUSTON (Reuters) -A vessel chartered by Chevron carrying some 300,000 barrels of Venezuelan oil was set to start discharging at a Venezuelan port on Thursday, according to shipping data and a source. It would be the last tanker to return its cargo following state company PDVSA's order to return the crude amid payment uncertainty related to U.S. sanctions. The Marshall Islands-flagged vessel, Dubai Attraction, on Thursday entered a berth in Amuay terminal, Venezuela, to start discharging the cargo it originally intended to export, LSEG shipping data showed.