SAN FRANCISCO (MarketWatch) -- Natural-gas futures climbed Thursday, after the Energy Information Administration reported a 31 billion cubic foot increase in U.S. inventories for the week ended April 12. Analysts polled by Platts had forecast a climb between 33 billion cubic feet and 37 billion. Total stocks now stand at 1.704 trillion cubic feet, down 794 billion cubic feet from the year-ago level and 74 billion cubic feet below the five-year average, the government said. May natural gas     (ngk13)   was at $4.32 per million British thermal units, up 11 cents, or 2.6%. It was trading at $4.20 shortly before the data