Pressure tests of five Johnson County, TX, drilling waste disposal wells in the area of a 4.0-magnitude earthquake that occurred May 7 "provide no conclusive evidence" the wells were a causal factor, the Railroad Commission of Texas (RRC) said Friday.

The finding comes two days after the commission held a show cause hearing requiring disposal well operator XTO Energy to demonstrate why its well should not be shut in because of quakes in its vicinity (see Shale Daily, June 11).

Tests of the five Johnson County wells were ordered after the May 7 quake according to rules that RRC adopted last year on seismic events (see Shale Daily, Oct. 28, 2014).

"Expert analysis by the commission's staff seismologist, geologists and petroleum engineers concluded these results do not indicate any bounding faults in the immediate vicinity of the wells tested," RRC said. "At this time, there is no conclusive evidence the disposal wells tested were a causal factor in the May 7 seismic event. The tests were conducted to help determine the effect of injection operations on pressures within subsurface rock formations."

The wells tested are all within 100 square miles of the estimated epicenter of the May quake. The well operators are Bosque Disposal System LLC, EOG Resources Inc. (two wells), MetroSaltwater Disposal Inc. and Pinnergy Ltd. All of the operators cooperated with the testing, the commission said.

"While we can't say at this time there is a connection, this is the beginning of the process, not the end, in analyzing and understanding whether there is any correlation and what, if any, action by the commission may be necessary in the future to protect public safety and our natural resources," said Craig Pearson, RRC staff seismologist.