Royal Dutch Shell PLC said Tuesday it has signed agreements to sell all of the Nigerian oil assets it put up for sale last year, the latest move by the Anglo-Dutch oil major to reduce its exposure to the West African nation.  A spokesman for Anglo-Dutch oil giant Shell said it—along with Italy’s Eni SpA and France’s Total SA —have signed an agreement to sell a 45% stake in Oil Mining Lease 18 to a consortium that includes Canadian company Mart Resources Inc. The terms of the deal weren’t disclosed.  The remaining 55% interest in the block—which produces up to 30,000 barrels a day—will be retained by the Nigerian National Petroleum Corp., Mart Resources said in a statement. The acquisition is subject to numerous terms and conditions including receipt of Nigerian government approval, it added.