After two years of studying earthquakes in the Barnett Shale, Cliff Frohlich, senior research scientist at the university’s Institute for Geophysics, concluded in his study that there is a correlation between earthquakes and underground disposal wells. The study was published this week in Proceedings of the National Academy of Sciences, a science journal.
Thanks to data provided from the EarthScope USArray program from November 2009 and September 2011, Frohlich was able to obtain seismic information from areas within the Barnett Shale.
According to its website, The EarthScope USArray Program is a transferable “network of 400 high-quality broadband seismographs that are being placed in temporary sites across the conterminous United States from west to east, and Alaska, in a regular grid pattern,”
The machines are placed approximately 70 kilometers apart. The grid of seismic machines was in Texas from 2009 until 2011 when Frohlich’s research was conducted. According to his study, there were about 25 machines located in the Barnett Shale where he was studying.
He said in a phone interview that when he began his study his intent was not to study injection wells but rather small earthquakes in the area. “I found that virtually all the ones (earthquakes) I located were close to injection wells,” he said.
In the study, it says, “He found that the most reliably located earthquakes — those that are accurate to within about 0.9 miles (1.5 kilometers) — occurred in eight groups, all within 2 miles (3.2 kilometers) of one or more injection wells. Before this study, the National Earthquake Information Center had only identified two earthquake groups in the area strongly associated with specific injection wells. This suggests injection-triggered earthquakes are far more common than is generally recognized.”
Although the study was conducted in the Barnett Shale, located in North Texas near the Dallas-Fort Worth area, when asked if the same could be true of earthquakes in the Eagle Ford Shale, he said, “I suppose so.”
Another aspect that was not covered in the study was the proximity of the earthquakes to fault lines.
“I suspect that wells with earthquakes have small fault lines, but I cannot prove it.”
While many small earthquakes were identified in the study, it said, “None of the quakes identified in the two-year study were strong enough to pose a danger to the public.”
Frohlich, a professional seismologist and UT employee of 34 years, hopes to continue his research.
“I am certainly looking at other areas,” he said.
He went on to explain that over the past five years there has been an increased interest in research relating to human-induced seismic activity.
His hope is that the research will continue and serve as an information source for both regulatory industries and companies looking to make changes to practices.