AUSTIN—Exxon Mobil Corp. told Texas regulators Wednesday that
the company's operations aren't behind a string of earthquakes in
the Dallas-Fort Worth area.
In the first hearing of its kind for the Railroad Commission of
Texas, officials with Exxon subsidiary XTO Energy Inc. presented
engineering and geological data they said show quakes that hit one
suburb in 2013 originated far deeper than a nearby well the company
used to inject wastewater from oil-and-gas operations back
underground.
"Those are deep-seated basement fault movements," said Tim
George, a lawyer for the company. "These are naturally occurring
movements, not man made."
A sharp increase in the number of earthquakes in the northern
part of Texas prompted the commission, which oversees oil-and-gas
industry activity, to launch a series of hearings on the topic.
EnerVest Operating Co., which operates a wastewater well in a Fort
Worth suburb is scheduled to appear before state examiners next
week. Four other energy companies, including EOG Inc., have been
asked to perform tests on several wastewater wells near Venus, 30
miles south of Dallas, where a magnitude 4.0 earthquake struck in
May.
EnerVest also disputes its well's role in causing the
earthquakes near the Fort Worth suburb of Azle. After reviewing
geological data, the company believes some were aftershocks from a
deeper, naturally occurring tremor, said Jud Walker, chief
operating officer.
"The conclusions they drew were a little strong," Mr. Walker
said of the SMU study.
Earlier this year researchers at Southern Methodist University
in Dallas published a study linking a cluster of earthquakes in the
Azle area between November 2013 and January 2014 to wastewater
wells operated by XTO and EnerVest. SMU researchers stand behind
that report, and said Wednesday that fault networks act as paths
for pressure changes to travel to critically stressed areas and
trigger earthquakes.
The wells aren't directly connected to drilling or hydraulically
fracturing oil and gas wells. Wastewater wells are used to inject
dirty water back underground that is left over from fracking
operations, as well as brine water that gets pumped out of oil and
gas wells. Those injections, SMU researchers say, likely
contributed to subsurface pressure changes that triggered
earthquakes near Fort Worth.
Studies done as far back as the 1960s have linked injection
wells to earthquakes deep in the ground, said Bill Ellsworth, a
geophysicist with the U.S. Geological Survey who worked on the SMU
research.
"That's where induced earthquakes usually occur," he said. "This
is science that has been understood for 50 years."
The U.S. Geological Survey says injection wells can cause
earthquakes, though not all do; such induced quakes can happen
miles away from the injection site.
Earthquakes big enough to feel were virtually unknown to the
Dallas-Fort Worth area until this decade when drilling and fracking
activity soared in the area, which is home to the gas-rich Barnett
Shale. The quakes have become common enough that some schools in
the region have begun to drill children on how to shelter under
their desks.
There has been a dramatic rise in tremors across the central
U.S. over the last six years, primarily caused by wastewater
disposal wells, according U.S. Geological Survey data. Between 1973
and 2008, the region averaged 24 quakes of magnitude 3 and larger
each year. But between 2009-14 that rate has steadily increased to
average 193 a year, peaking in 2014 with 688 earthquakes.
Texas regulators revised permitting rules last November so they
could modify, suspend or even end a wastewater disposal well's
approval if scientific data showed it could be contributing to
earthquakes.
The Railroad Commission's scrutiny will continue said
Commissioner Ryan Sitton. The increased frequency of earthquakes in
Texas is a big concern, he said, noting they are happening both
close to and far from oil-and-gas operations.
"We need to research it," Mr. Sitton said, acknowledging that
public fear of the earthquakes has led some communities to try to
ban the industry from their towns. "We have an opportunity to keep
this from becoming a political issue."
Write to Erin Ailworth at Erin.Ailworth@wsj.com
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