AZLE, Texas (AP) — Earthquakes used to be almost unheard
of on the vast stretches of prairie that unfold across Texas, Kansas and
Oklahoma.
But in recent years, temblors have become commonplace.
Oklahoma recorded nearly 150 of them between January and the start of
May. Most were too weak to cause serious damage or endanger lives. Yet
they’ve rattled nerves and raised suspicions that the shaking might be
connected to the oil and gas drilling method known as hydraulic
fracturing, especially the wells in which the industry disposes of its
wastewater.
Now after years of being harangued by anxious
residents, governments in all three states are finally confronting the
issue, reviewing scientific data, holding public discussions and
considering new regulations.
The latest example comes Thursday in
Edmond, Oklahoma, where hundreds of people are expected to turn out for a
town hall meeting that will include the state agency that regulates oil
and gas drilling and the Oklahoma Geological Survey.
States with
historically few earthquakes are trying to reconcile the scientific data
with the interests of their citizens and the oil and gas industry.
"This
is all about managing risks," said Oklahoma Corporation Commission
spokesman Matt Skinner. "It’s a little more complicated than that
because, of course, we’re managing perceived risks. There’s been no
definitive answers, but we’re not waiting for one. We have to go with
what the data suggests."
Regulators from each state met for the
first time in March in Oklahoma City to exchange information on the
quakes and discuss toughening standards on the lightly regulated
business of fracking wastewater disposal.
In Texas, residents from
Azle, a town northwest of Fort Worth that has endured hundreds of small
quakes, went to the state Capitol earlier this year to demand action by
the state’s chief oil and gas regulator, known as the Railroad
Commission. The commission hired the first-ever state seismologist, and
lawmakers formed the House Subcommittee on Seismic Activity.
After
Kansas recorded 56 earthquakes between last October and April, the
governor appointed a three-member task force to address the issue.
Seismologists
already know that hydraulic fracturing — which involves blasting water,
sand and chemicals deep into underground rock formations to free oil
and gas — can cause microquakes that are rarely strong enough to
register on monitoring equipment.
However, fracking also generates
vast amounts of wastewater, far more than traditional drilling methods.
The water is discarded by pumping it into so-called injection wells,
which send the waste thousands of feet underground. No one knows for
certain exactly what happens to the liquids after that. Scientists
wonder whether they could trigger quakes by increasing underground
pressures and lubricating faults.
Another concern is whether
injection well operators could be pumping either too much water into the
ground or pumping it at exceedingly high pressures.
ExxonMobil
subsidiary XTO Energy has pumped an average 281,000 gallons — about 94
tanker truckloads — of wastewater into its Azle wells nearly every day
for more than two years, according to data published by the Railroad
Commission earlier this month.
In recent weeks, nighttime shaking
in Oklahoma City has been strong enough to wake residents. The state
experienced 145 quakes of 3.0 magnitude or greater between January and
May 2, 2014, according to the Oklahoma Geological Survey.
That compares with an average of two such quakes from 1978 to 2008.
Oklahoma
Gov. Mary Fallin approved new testing and monitoring rules for
injection wells that require well operators to collect daily information
on well volume and pressure, instead of monthly. The rules take effect
in September, Skinner said.
Southern Methodist University
researchers have recorded more than 300 quakes around Azle since early
December, with some days experiencing swarms of hundreds of microquakes
and other days none.
The geophysicists are measuring the
earthquakes to plot out an ancient fault line and developing models that
look at how fluids flow through the layer of rock where the earthquakes
are originating.
Researchers are also looking at whether fluids
from disposal wells in Azle and around North Texas moved through the
ground and helped stimulate that fault, or if earthquakes are occurring
naturally.
Members of the SMU team previously studied two other
earthquake sequences in North Texas and concluded that there was a
plausible link between the earthquakes and nearby injection wells. North
Texas has had 70 earthquakes since 2008 as reported by the USGS,
compared with a single quake, in 1950, reported in the region before
then.
Still, seismologists — and the oil and gas industry — have
taken pains to point out that a clear correlation has not yet been
established.
"The link between injection wells and earthquakes is
something we are still in the process of studying," said Heather DeShon,
associate professor of geophysics at SMU.
Nationwide, the United
States has more than 150,000 injection wells, according to the Society
of Petroleum Engineers, and only a handful have been proven to induce
quakes.
Nonetheless, ExxonMobil is supporting the SMU study, company spokesman Richard Keil said.
"We’re sort of in wait-and-see mode," he said.