BANGKOK -- Thai coal company Banpu will purchase shale assets in the U.S. state of Texas for $770 million under a deal announced Wednesday, more than tripling its natural gas output amid growing investor pressure for cleaner fuels. Banpu aims to complete the transaction for the Barnett Shale operations, now run by U.S.-based Devon Energy, in the second quarter of 2020. The assets have been in operation for two decades and produce a net 600 million cu. feet of natural gas a day on average. Total reserves amount to 3.5 trillion cu. feet, according to the announcement.