After wrapping up a round of testing, Texas regulators say they have found no evidence that injecting oilfield waste into five disposal wells triggered the largest recorded earthquake in North Texas’ history.
“At this time, there is no conclusive evidence the disposal wells tested were a causal factor in the May 7 seismic event,” the Texas Railroad Commission said Friday in a news release.
Last month, a 4.0-magnitude earthquake hit Johnson County, leading to a few reports of minor damage. It was the most powerful ever recorded in the Barnett Shale region, including more than 50 quakes that have struck since November 2013 — a surge that has coincided with the proliferation of disposal wells, deep resting places for liquid oil and gas waste injected underground at high pressures.
Under rules adopted last year, the Railroad Commission ordered testing at five disposal wells, which the four companies that operate them voluntarily shut down. On Friday, the commission said its analysis of “fall-off pressure”– tests to determine the effects of injections at the well sites – turned up no fault patterns nearby that could have been related to the earthquakes.
“While we can’t say at this time there is a connection,” Craig Pearson, the agency’s seismologist, said in a statement, “this is the beginning of the process, not the end in analyzing and understanding whether there is any correlation and what, if any action by the Commission may be necessary in the future to protect public safety and our natural resources.”
The disposal wells in question are operated by Bosque Disposal System, LLC; EOG Resources, Inc.; MetroSaltwater Disposal, Inc; and Pinnergy, Ltd.
The commission’s announcement comes the same week that another disposal well operator, XTO Energy, an ExxonMobil subsidiary, argued that it was not responsible for a series of earthquakes that shook the towns of Reno and Azle in late 2013 through early 2014.
On Wednesday, the company argued at an eight-hour commission hearing that the quakes hit some 2.5 miles below its wastewater injection, indicating that they occurred naturally.
The commission ordered the “show cause” hearing after a team of researchers led by Southern Methodist University concluded that industry activity “most likely” triggered the earthquakes. The peer-reviewed research, published in April, linked the earthquakes to wells operated by XTO Energy and EnerVest.
The operators’ withdrawal of brine – naturally salty water removed during oil and gas drilling – and the high-pressure injection of huge volumes of wastewater from gas wells were to blame, that study concluded.
EnerVest is scheduled to argue its case at the commission on Monday.
The SMU researchers say they won’t wade into the policy debate at the commission, but they stand by their work.
“We will not be providing comments on the hearings or on any non-peer reviewed science being presented at the hearings,” the researchers said in a statement this week. “We remain confident in the conclusions presented in our peer-reviewed publication, which was based on multiple lines of evidence.”
The SMU team has not had the chance to fully study the 4.0 Johnson County quake, Kim Cobb, a university spokeswoman, said Friday, but it has added it to its list of interests.
In May, Heather DeShon, an SMU professor of geophysics, said she was not surprised by the larger temblor.
“There have been a series of magnitude 3 and greater earthquakes in the Johnson County area. If you have movement on a fault and change the stresses, you increase the likelihood of additional earthquakes, she said. “This illustrates that we all need to think about the possibility of larger earthquakes in the region where we live.”
Scientists have known for decades that injecting fluid deep underground could trigger earthquakes. Neighboring Oklahoma has seen an increase in earthquakes even greater than Texas has, and has surpassed California as the country’s most quake-prone state. The USGS and Oklahoma Geological Survey say wastewater disposal probably contributes to the trend.
Still, researchers point out, thousands of disposal wells have not been linked to earthquakes.
Disclosure: Southern Methodist University and ExxonMobil are corporate sponsors of The Texas Tribune. A complete list of Tribune donors and sponsors can be viewed here.