M ore than a year after it delayed a decision on a major new oil sands expansion, Royal Dutch Shell PLC RDS.A-N is backing further away from Canada’s richest crude resource. Shell will dramatically slow its future growth in the Fort McMurray area, according to chief executive officer Peter Voser, who said that high costs in the oil sands are the reason the company is steering exploration dollars to other parts of the world, including the Gulf of Mexico and Kazakhstan. A spate of decisions by other international oil companies to revive projects has created hope that the oil sands are recovering from the beating they sustained at the hands of high construction costs and lower oil prices