By Texas Press Reports —
A recent wave of small earthquakes in and around the Eagle Ford
formation in Texas was probably the result of extracting oil and in some
cases water used for hydraulic fracturing, according to a study.
Clusters of small-magnitude seismic events between November 2009 and
September 2011 were “often associated with fluid extraction,” according
to the study scheduled to appear this week in the online edition of the
journal Earth and Planetary Science Letters.
The study follows previous research that links earthquakes to the disposal of drilling wastewater by injecting it underground.
Oil production in the Eagle Ford basin in southern Texas, has surged
to about 600,000 barrels a day from 15,000 barrels in 2010, according to
the Texas Railroad Commission. Production is up as drillers use
hydraulic fracturing, or fracking, a process in which millions of
gallons of chemically-treated water and sand are pumped underground, to
free hydrocarbons.
“You're pulling out large volumes,” Cliff Frohlich, co-author of the
study and associate director of the Institute for Geophysics at the
University of Texas, said in an interview. “You remove stuff, and stuff
adjusts or slumps around and either above or below the area where you
remove it.”
The drilling stage in which liquids are injected underground wasn't implicated, he said.
“We don't see any evidence that injection in the Eagle Ford appears
to routinely cause earthquakes,” Frohlich said.Seismograph Stations Frohlich used data from temporary seismograph stations to identify 62
small earthquakes, almost all of which occurred near wells extracting
oil or water. In Dimmit County, Texas, 21 of 22 earthquakes were within
6.2 miles (10 kilometers) of wells used to produce water for fracking
and agriculture, according to the study.
A 2012 study by Frohlich of the Barnett Shale in northern Texas found
that earthquakes were triggered by injecting drilling wastewater
underground.
Scientists have linked Oklahoma's biggest recorded earthquake to the
disposal of wastewater from oil production. The 5.7-magnitude quake in
2011 followed an 11-fold bump in seismic activity across the central
U.S. in recent years as disposal wells are created to handle increases
in wastewater from hydraulic fracturing, or fracking, according to
researchers at the University of Oklahoma, Columbia University and the
U.S. Geological Survey.
The researchers said the results point to the long-term risks the
thousands of wells pose and show a need for better monitoring and
government oversight.
“This issue really boils down to effective risk management and
continuously improving production processes,” Steve Everley, a spokesman
for Energy in Depth, a group representing gas drillers, said in an
e-mail. “The industry has the tools to do just that, has been doing it,
and will continue to do it well into the future.”
