A report published Monday by the group Proceedings of the National Academy of Sciences of the United States asserts that there is a link between dozens of small earthquakes in Texas’ Barnett Shale and wastewater injection wells that support natural gas drilling.

Cliff Frohlich, a geophysics professor at the University of Texas and the report’s author, said he analyzed data taken from temporary seismographs that were deployed within a 70-kilometer grid in the Barnett from November 2009 to September 2011. Frohlich said he was able to identify 67 earthquakes from the data, more than eight times the number of quakes reported by the National Earthquake Information Center.

“All 24 of the most reliably located epicenters occurred in eight groups within 3.2 kilometers of one or more injection wells,” Frohlich said. “This suggests injection-triggered earthquakes are more common than is generally recognized.”

Frohlich added that all of the wastewater wells nearest the earthquake epicenters had reported maximum monthly injection rates in excess of 150,000 barrels per month since October 2006. But the researcher added that while nine of 27 wastewater wells in Johnson County, TX, were near earthquake epicenters, there were no reported earthquakes near wastewater wells with similar injection rates.

“A plausible hypothesis to explain these observations is that injection only triggers earthquakes if injected fluids reach and relieve friction on a suitably oriented, nearby fault that is experiencing regional tectonic stress,” Frohlich said. “Testing this hypothesis would require identifying geographic regions where there is interpreted subsurface structure information available to determine whether there are faults near seismically active and seismically quiescent injection wells.”

In mid-July, Johnson County reported about 10 small earthquakes within a one-month period (see Shale Daily, July 17). The quakes caused no damage or injuries.

Regulators with the Railroad Commission of Texas asserted that two earthquakes in May near Timpson, TX, in the eastern part of the state, were unlikely to have been caused by natural gas drilling or wastewater injection wells (see Shale Daily, May 22). But researchers at the U.S. Geological Survey (USGS) have cited drilling-related injection wells as the reason for a “remarkable” uptick in seismic activity (see Shale Daily, April 2).

Scientists from the USGS earthquake research center in Menlo Park, CA, said there has been a six-fold increase in the number of earthquakes of 3.0 magnitude or greater since 2001, over 20th century levels. However, state geologists in Colorado and Oklahoma disputed this finding, at least in its application to the Midcontinent (see Shale Daily, April 17).

In March the Ohio Department of Natural Resources (ODNR) said a dozen small earthquakes in northeastern Ohio over the last year may have been triggered by a wastewater disposal well in Youngstown (see Shale Daily, March 12). Gov. John Kasich then subsequently issued an executive order calling for tougher regulation of injection wells (see Shale Daily, July 13).

Last year regulators in Arkansas established a moratorium on wastewater disposal wells in an area of the Fayetteville Shale after similar quake activity was reported there (see Shale Daily, July 29, 2011; March 4, 2011).