Gas Injection Likely Triggers Earthquakes But Only Under Right Conditions

The injection of massive amounts of gas underground may have triggered a spate of small earthquakes near Snyder, Texas between 2006 and 2011, a new study found.

Though no injuries or severe damage were linked to the earthquakes, researchers note that the study marks the first time underground gas injection has been linked to quakes greater than magnitude 3.

Published in the Proceedings of the National Academy of Sciences, the study also discovered that similar rates of injection failed to trigger quakes in other areas -- an observation that adds weight to the possibility that underground gas injection does not result in major seismic events in many geologic settings.

The area examined, located in northwest Texas, is home to three large oil and gas fields that have been at work producing petroleum for more than half a century. Operators first began injecting CO2 in one of the fields in 1971 in order to boost production and a second field in 2001.

Wei Gan and Cliff Frohlich of the University of Texas at Austin's Institute for Geophysics used a network of seismometers to identify 93 earthquakes that took place in the area of the second field known as the Cogdell between March 2009 to December 2010, all of which were greater than magnitude 3. These were followed by an even larger 4.4 magnitude earthquake in September 2011.

"What's interesting is we have an example in Cogdell field, but there are other fields nearby that have experienced similar CO2 flooding without triggering earthquakes," said Frohlich, associate director of the Institute for Geophysics, a research unit in the Jackson School of Geosciences. "So the question is: Why does it happen in one area and not others?"

One hypothesis has to do with the possibility of more geological faults in the Cogdell area, rendering the area more fragile.

In a previous study published in the same journal, earthquake researchers Mark Zoback and Steven Gorelick concluded that "there is a high probability that earthquakes will be triggered by injection of large volumes of CO2" during carbon capture and storage.

Based on their own findings, Frohlich argues that the threat may not be a universal one.

"The fact that the different fields responded differently to CO2 injection and that no other gas injection sites in the world have been linked to earthquakes with magnitudes as large as 3 suggest that despite Zoback and Gorelick's concerns, it is possible that in many locations large-volume CO2 injection may not induce earthquakes."