Large Volume of Underground Gas Injection Linked to Earthquakes Near Snyder, Texas

A latest study links a series of small earthquakes near Synder in Texas to gas injections between 2006 and 2011.

A new study led by researchers Wei Gan and Cliff Frohlich at the University of Texas, links a series of small earthquakes near Snyder, Texas, between 2006-2011 with the underground gas injection, mainly of carbon dioxide [CO2]. This finding is relevant to the process of capturing and storing CO2 underground.

This study claims that underground injection of large volume gas caused earthquakes in Snyder. It also highlights the point that in other fields, the same rate of injection did not trigger any comparable quakes, reinforcing the idea that underground gas injection does not trigger seismic events in different geological settings.

 No injuries or damage were reported during those quakes. This is the first time underground gas injection has been associated with quakes of magnitude more than 3. 

The researchers conducted a study on a northwest Texas area that has three large oil and gas fields namely the Cogdell Field, the Salt Creek Field and the Scurry Area Canyon Reef Operators Committee unit (SACROC). These fields have successfully produced petroleum since the 1950s.

In order to enhance the petroleum production, they started injecting CO2 in the SACROC field in 1971.  This process is called CO2 Enhanced Oil Recovery [CO2 EOR]. In 2001, CO2 EOR was started in the Cogdell field and by 2004 this process increased. With the help of high resolution temporary network of seisomometers, seismic data from 2009-2010 was collected by the EarthScope USArray Program. Nearly 93 earthquakes in the Cogdell area from March 2009-December 2010 were identified.

Out of the 93 quakes identified, three had magnitudes greater than 3 and in 2011, earthquakes with larger magnitude of 4.4 occurred in the Cogdell area. Most of these quakes occurred in northeast-southwest trending linear clusters. They also detected quakes with low magnitude of 1.5.

 Examining the data on injections and extractions of fluids and gases, the researchers concluded that the earthquakes were associated with the elevation in the CO2 EOR in the Cogdell area.

"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?"

Prior to this study, a paper published last year in the Proceeding of the National Academy of Sciences by researchers at the Stanford University claimed that there is a high probability that earthquakes are triggered by injection of large volume of CO2, during CCS.

According to Frohlich, different fields respond differently to CO2 injection and it's a fact that no other gas injection sites have been associated with earthquakes of magnitude greater than 3 despite the Standford researchers' concern.

Frohlich suggests, "One possible explanation for the different response to gas injection in the three fields might be that there are geological faults in the Cogdell area that are primed and ready to move when pressures from large volumes of gas reduce friction on these faults. The other two fields might not have such faults."

The researchers also analyzed the data collected on injections and extractions of oil, water and gas in the study area. They noticed that since 1990, the rate of liquid injection and extraction, as well as gas produced, remained fairly constant in all three oil and gas fields. The only significant change noticed was the increase in the rate of gas injection, mainly CO2, in the Cogdell field from the beginning of 2004.

The findings are published in the journal Proceedings of the National Academy of Sciences.