In the frosty swamplands of West Siberia, the drilling rigs of oil giant OAO Lukoil are helping raise Russia’s oil output to its highest levels since the breakup of the Soviet Union a quarter century ago. But falling crude prices , U.S.-led sanctions and diminished oil exploration threaten Russia’s oil industry and raise questions about its capacity to continue underwriting President Vladimir Putin ’s ambitions at home and abroad. While recent increases in Russian oil output have helped cushion the sharp price fall, Mr. Putin is so squeezed for cash , his government postponed a planned reduction in oil-export duties this year. Executives say they fear the postponement could be extended, diverting money to Moscow that could be invested in new drilling and exploration to supplement aging oil fields. “We will have to limit our spending and that will lead to a fall […]