Welders work inside a steel construction tube at Cnooc Ltd.'s marine engineering facility in Shenzhen, China. China, estimated to hold triple the shale reserves of the U.S., has yet to produce the fuel commercially because its drillers lack technology and face tougher geology . Explorers including Cnooc Ltd. have bid for $100 billion of energy assets from Australia to Canada since 2008, including so-called unconventional resources, to boost reserves and gain expertise. Photographer: Paul Hilton/Bloomberg