from Sci-News
A new study published this week in the Proceedings of the National Academy of Sciences correlates 93 small earthquakes near Snyder, Texas between 2009 and 2011 with the underground injection of large volumes of gas, primarily carbon dioxide.
This illustration shows how carbon dioxide and water can be used to flush residual oil from a subsurface rock formation between wells. Image credit: U.S. Department of Energy.
The study focused on an area of northwest Texas with three large oil and gas fields – the Cogdell field, the Salt Creek field and the Scurry Area Canyon Reef Operators Committee unit – which have all produced petroleum since the 1950s.
Operators began injecting carbon dioxide in the Scurry Area Canyon Reef Operators Committee field in 1971 to boost petroleum production, a process known as Carbon Dioxide Enhanced Oil Recovery.
In the Cogdell field, operators began the process in 2001, with a significant increase starting in 2004.
Because carbon dioxide has been injected at large volumes for many years, U.S. Department of Energy has funded research in this region to explore the potential impacts of carbon capture and storage, a proposed technique for reducing greenhouse gas emissions by capturing carbon dioxide and injecting it deep underground for long-term storage.
Using seismic data collected between March 2009 and December 2010 by the EarthScope USArray Program, a National Science Foundation-funded network of broadband seismometers deployed from the Canadian border to the Gulf of Mexico, study co-authors identified 93 earthquakes in the Cogdell area from March 2009 to December 2010, three of which were greater than magnitude 3. An even larger earthquake, with magnitude 4.4, occurred in Cogdell in September 2011.
Using data on injections and extractions of fluids and gases, they concluded that the earthquakes were correlated with the increase in Carbon Dioxide Enhanced Oil Recovery in Cogdell.
“What’s interesting is we have an example in Cogdell field, but there are other fields nearby that have experienced similar carbon dioxide flooding without triggering earthquakes,” said co-author Dr Cliff Frohlich from University of Texas at Austin’s Institute for Geophysics.
Map of the study area, showing 2009–2011 earthquakes, red circles, located in this study, and wells injecting water, yellow squares. Image credit: Wei Gana / Cliff Frohlich.
“So the question is: Why does it happen in one area and not others?”
He said 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.
“An important next step in understanding seismic risks for proposed carbon capture and storage projects would be to create geological models of Cogdell and other nearby fields to better understand why they respond differently to gas injection.”