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
09/03/2015
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