** Natural gas companies' shares rise, tracking futures
** U.S. prices NGC1 up 5.6% at $2.26 per mln British thermal units on smaller-than-expected storage build, rising gas flows to LNG export plants and a continued decline in output so far this month NGA/
** LNG producers NextDecade NEXT.O up 7.1%, Chesapeake CHK.O 1.6%, CNX Resources CNX.N 1.1%
** ETFs United States Natural Gas Fund UNG.P up 5.3% and ProShares Ultra Bloomberg Natural Gas BOIL.P rises 7.4%
(Reporting by Seher Dareen in Bengaluru)