The 56 percent drop in oil prices in the last six months is fueling more than just jet engines and road trips. It’s also burning through the cushy budget surpluses enjoyed by some of the world’s biggest oil-producing nations.  Saudi Arabia, the world’s top producer of crude, will see the budget surplus it has enjoyed in the past turn into a deficit of 4.7 percent of gross domestic product this year, according to the median estimate of eight economists surveyed by Bloomberg. That would be the first shortfall since 2009, according to  International Monetary Fund  data. The Middle Eastern nation, which derives about 90 percent of its budget revenue from oil, recorded a surplus of 8.7 percent of GDP in 2013. (Data for 2014 surpluses or deficits aren’t yet available in many countries, so we’re using 2013 for comparisons.) Oil exporters Kuwait, Qatar and the United Arab Emirates will also see their surpluses […]