(Reuters) - Some U.S. oil and gas producers in the Gulf of Mexico shut in production and were evacuating energy infrastructure on Saturday as Tropical Storm Isaac headed for Cuba on a path toward the eastern part of the Gulf. The U.S. Bureau of Safety and Environmental Enforcement said on Saturday that 8.63 percent of the Gulf's oil output and 1.62 percent of natural gas production per day was shut down. The Gulf of Mexico accounts for about 23 percent of U.S. oil production and 7 percent of natural gas output, according to the U.S. Energy Information Administration. About 30 percent of U.S. ...