The U.S. oil boom has put European refineries out of business and undercut West African crude suppliers. Now domestic drillers threaten to roil Asian markets and challenge producers in the Middle East and South America. Fifteen European refineries have closed in the past five years, with a 16th due to shut this year, the International Energy Agency said, as the U.S. went from depending on fuel from Europe to being a major exporter to the region. Nigeria, which used to send the equivalent of a dozen supertankers of crude a month to the U.S., now ships fewer than three, according to the U.S. Energy Information Administration. And cheap oil from the Rocky Mountains, where output has grown 31 percent since 2011, will soon allow West Coast companies to cut back on imports of pricier grades from Saudi Arabia and Venezuela that they process for customers in […]