Thursday, September 3, 2015

Texas Railroad Commission Examines Cause of Earthquakes in the Azle/Reno area

On August 31, 2015, the Railroad Commission of Texas (RRC) issued a Proposal for Decision as to whether a disposal well operated by XTO Energy, Inc., in the Barnett Shale Formation was a contributing cause to seismic activity in the Azle-Reno area. The Commission concluded that evidence in the record was not sufficient to support the claim that XTO’s disposal well caused the 2013 earthquakes in said area.

On April 24, 2015, RRC called a hearing to give XTO an opportunity to show cause why the waste disposal well permit should not be revoked as a response to the study “Causal Factors for Seismicity Near Azle, Texas” published in the journal Nature Communications on April 21, 2015. The study reported that “subsurface stress changes associated with brine production and wastewater injection represents the most probable cause of recent earthquakes in the Azle area.”

RRC examiners found that earthquakes occurred “along the Azle fault below the Ellenburger Formation injection zone in the Precambrian crystalline basement rock at a depth of about 20,000 feet” while the study’s “groundwater model estimated pore pressure changes at a depth of about 10,000 feet, at the base of the Ellenburger Formation.” As a result, because the study did not model pressures into the Precambrian crystalline basement rock and associated fault zones, examiners determined that there was no evidence showing that the waste disposal well transferred energy to the location of initial rupture at a depth of 20,000 feet. RRC examiners concluded that XTO’s waste disposal well permit should be maintained.

Written by Chloe Marie - Research Fellow

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