A paper recently published in the Proceedings of the National Academy of Sciences concludes that a series of earthquakes in Texas may have been triggered by injection of CO2 and other gases into an oil field. The researchers found that 18 earthquakes with magnitudes of 3 or greater and tens of smaller earthquakes occurred between 2006 and 2011 near the Codgell Oil Field outside Snyder, TX. Generally speaking, earthquakes must be larger than magnitude 3 in order to be felt at the surface by humans.
This field has a history of induced earthquakes related to an earlier phase of production, from 1957 to 1982, when water was injected into the field to increase the flow of oil (aka “water flooding”). However, there was a gap in seismic activity between the time when water flooding ended and when CO2 injection began, leading the researchers to suggest that CO2 injection may have contributed to triggering these more recent earthquakes.
Carbon dioxide is sometimes injected in aging oil fields to boost production, in a process known as CO2 enhanced oil recovery (CO2-EOR). Earlier this year, the National Academy of Sciences published a comprehensive study on induced seismicity related to energy production, and found that “(t)o date, EOR has not been associated with induced seismicity.” If the link between CO2 injection and the Texas earthquakes is confirmed, this will be the first documented instance of CO2-EOR inducing earthquakes large enough to be felt at the surface.
One interesting observation of the study is that nearby oil fields similar to Codgell, which have similar production histories including years of water flooding followed by gas injection, are not associated with any earthquakes. One of these fields is the SACROC unit, which is the site of a major, multi-year, multi-disciplinary research project on CO2-EOR, including extensive geologic and geophysical investigations. As the researchers suggest, additional focused research at these fields could help explain this observation and provide crucial insight into why some injection projects result in induced seismicity while others do not.
Carbon dioxide can also be injected into deep geologic formations to be permanently stored as part of a carbon capture and sequestration (CCS) project. This is referred to as geologic sequestration of CO2 (GS). Concerns have been raised about what this new research out of Texas could mean for large-scale CCS and GS. As my colleague George Peridas wrote on this topic last year, earthquakes caused by human activities is an issue that deserves more attention. This includes both additional scientific research to understand the causes and risks even better, and above all improved regulation to manage the risks.
Currently there are significant differences between the regulations that govern CO2-EOR and those that govern GS, despite the fact that both have similar environmental risks. Both are regulated under EPA’s Underground Injection Control (UIC) program, but CO2-EOR falls under the less stringent Class II rules while GS falls under the more stringent Class VI rules. Class II rules do not require operators to consider seismic risk when deciding where to locate injection wells or how to operate them; Class VI rules do. EPA clearly recognizes that induced earthquakes are a risk associated with underground injection – as scientists have known for decades – yet fails to manage this risk consistently.
EPA and the states must do better. This new research puts a spotlight on the gaps in Class II regulations. Extensive work has been done to develop strategies to mitigate the risk of induced seismicity, including work by Lawrence Berkeley National Laboratory and the National Academy of Sciences. These strategies could easily be adopted by regulators and operators alike. The regulations for CO2-EOR must be updated to accurately reflect the risk of induced seismicity in order to protect the environment and the public.
The findings of this new study do not call into question the overall viability of injecting and storing CO2 underground. But they are a reminder that it needs to be done right.