The Texas Railroad Commission said Friday that it was considering shutting down two wastewater disposal wells in North Texas' Barnett Shale after they were linked to seismic activity in the area. A study led by scientists at Southern Methodist University published earlier this week presented evidence that a series of earthquakes around the rural town of Azle in late 2013 were caused by two disposal wells operated by oil and gas companies XTO Energy - the Fort Worth subsidiary of Exxon Mobil - and Houston-based EnerVest.