This week, the U.S. Geological Survey (USGS) released a report identifying the areas of the United States where induced seismicity has been linked to wastewater injection wells. Unfortunately, the report strangely loops natural earthquakes in with seismic events that could have been induced by injection activities, and in one notable example, ascribes fault to oil and gas production based upon research that concluded exactly the opposite.
While the report certainly adds to the growing body of literature on the topic, it should be noted that the areas it has identified – and, subsequently, the kinds of activities that may need to change in those areas – have already been incorporated into the public’s understanding. The study’s call for collaboration is currently being met as industry, scientists and regulators have been working together to address this important issue through best practices and updated regulations. In a nutshell, what’s outlined in the report is useful, but for the companies and regulators on the ground who are working to address the issue, there is likely very little “new” here.
Here are the five important things to keep in mind while evaluating the new report:
Fact #1: USGS’s report is all inclusive – assumes all seismicity is induced seismicity
It’s important to keep in mind that the report assumes that all potential induced seismic events are actual induced seismic events and acknowledges the following:
“We acknowledge that natural earthquakes could occur within the defined zones during the stated time windows; however, we treat the seismicity as induced for this study because the earthquakes are all located near deep fluid injection wells or other industrial activities capable of inducing earthquakes.” (p. 11; emphasis added)
In other words, the USGS is admitting that it is referring to naturally occurring earthquakes as induced, and it is blaming wastewater injection wells for natural events. It may have been beyond the scope of the USGS report to model the subsurface to determine which of these were natural and which were manmade (and, to be fair, many scientists have said that’s a difficult if not impossible task). But, it is worth emphasizing that at least some of these earthquakes – and, by extension, some of the “risk” outlined by USGS – are a result of natural causes.
The researchers add,
“The increased rate of earthquakes (including potentially induced earthquakes) translates into an increased earthquake hazard. The phrases “potentially induced seismicity,” “induced seismicity,” “potentially induced earthquakes” or “induced earthquakes” are used interchangeably in this report, and indicate that the seismicity in a given region has shown an increased earthquake rate that can be attributed to human activities, such as fluid injection or extraction. We acknowledge that this classification is based on circumstantial evidence and scientific judgment.” (p. 4; emphasis added).
To demonstrate the problem with USGS’s “all-inclusive” tactic, the researchers included a seismic event in the 1990s in southwest Alabama. The definitive report on that seismic event – which the USGS cited – concluded, “no clear temporal correlation between hydrocarbon recovery and the 1997 sequence has been established.”
Fact #2: More than 99 percent of injection wells operate without seismicity
While the USGS focuses this report on the particular areas where induced seismicity is occurring, what it does not evaluate is the specific number of wells that have been linked to seismicity, although it does point out that “induced seismicity does not occur near every disposal well.” Importantly, out of the tens of thousands of wells operating across the United States, only a fraction of them have been linked to seismic activity.
As the USGS has pointed out previously,
“Of more than 150,000 Class II injection wells in the United States, roughly 40,000 are waste fluid disposal wells for oil and gas operations. Only a small fraction of these disposal wells have induced earthquakes that are large enough to be of concern to the public.” (emphasis added)
The National Research Council – part of the prestigious National Academies – has concluded:
“Injection for disposal of wastewater derived from energy technologies into the subsurface does pose some risk for induced seismicity, but very few events have been documented over the past several decades relative to the large number of disposal wells in operation.” (emphasis added)
A study released last summer in Science magazine concluded that just four injection wells could be responsible for 20 percent of the earthquakes, not just in Oklahoma, but throughout the entire central United States.
A major report recently released by the U.S. Environmental Protection Agency, which was intended to help clarify induced seismicity for the purpose of better managing risks, concluded that “very few” of the tens of thousands of disposal wells in the United States have produced any notable seismic activity.
EID recently released a report looking specifically at the number of wells linked to seismicity in the Barnett Shale in Texas and found, using data from the Railroad Commission of Texas, that more than 99 percent of injection wells have not been associated with felt seismic events. In other words, only one-tenth of one-percent of injection wells across the Barnett Shale – or fewer than two dozen of them – have any sort of plausible connection to earthquakes.
While this small number of wells certainly needs to be addressed – which is why producers, scientists and regulators are collaborating on mitigation efforts – this is very important context.
Fact #3: Mitigating induced seismicity requires a site by site approach
Effectively addressing induced seismicity from injection wells requires a site by site approach, taking into account the fact that geological conditions are not uniform and similar wells in different areas may or may not have any nearby seismicity. As numerous peer-reviewed studies have found, the assessment should be based on downhole pressure, volume, and location, including the orientation of faults.
That’s actually something that the new USGS report emphasizes,
“In a few places, seismic activity increased as pumping began but diminished or ceased when the pumping stopped, sometimes with a lag time before the earthquake activity terminated (for example, Rocky Mountain Arsenal, Colorado). It is important to recognize that the induced seismicity behavior differs substantially between zones, so these rate characteristics need to be evaluated for each zone separately.” (p. 5; emphasis added)
In other words, a blanket, one size fits all approach is not an appropriate solution since every well is operating in different geologies and conditions.
Fact #4: There are straightforward ways to reduce the risk, which industry and regulators are implementing
As Bill Ellsworth of the USGS said about the new report,
“We think society can manage the hazard. We don’t have to stop production of oil and gas, but we think we can do so in a way that will minimize the earthquake hazard.” (emphasis added)
In states like Oklahoma, the State Oil & Gas Regulatory Exchange created an induced seismicity working group, which brings together state regulatory agencies and geological surveys, along with the Ground Water Protection Council, to share science and research. In these collaborative efforts, fault data and other geological information are shared with the state geological survey, the Corporation Commission, and research institutions such as Stanford, the University of Oklahoma, and Southern Methodist University (among others). The industry has also helped to secure funding for additional seismic monitoring throughout Oklahoma.
This kind of collaboration has happened in conjunction with major regulatory and operational changes in Texas and Oklahoma, which is where much of the induced earthquake discussion is focused. In Oklahoma, the Corporation Commission has increased its scrutiny for new injection wells in seismically active areas. The state also works under a “traffic light system,” recommended by the National Academy of Sciences. Under that system, no injection wells are permitted in “red-light” zones, or areas where seismicity is actively occurring. Wells with a “yellow-light” status are more closely monitored, which means the state can even shut them down if their operation leads to seismicity.
Fact #5: Hydraulic fracturing does not pose a credible risk for induced seismicity
Study after study has shown that the risk of induced seismicity from hydraulic fracturing itself is exceedingly low. The National Research Council has looked into this issue and come to this conclusion:
“The process of hydraulic fracturing a well as presently implemented for shale gas recovery does not pose a high risk for inducing felt seismic events.”
Cliff Frohlich, Associate Director of the Institute for Geophysics at the University of Texas at Austin, studied seismicity in the Eagle Ford Shale and found:
“Although there is a considerable amount of hydraulic fracturing activity in the Eagle Ford, we don’t see a strong signal associated with that and earthquakes.”
According to a report from Durham University:
“Hydraulic fracturing of sedimentary rocks, for recovery of gas from shale, usually generates very small magnitude earthquakes only […] It should be noted, however, that after hundreds of thousands of fracturing operations, only three examples of felt seismicity have been documented. The likelihood of inducing felt seismicity by hydraulic fracturing is thus extremely small but cannot be ruled out.” (p.18, emphasis added)
Stanford geophysicist Mark Zoback has also explained the small effect these events have:
“These microseismic events [from hydraulically fracturing a well] affect a very small volume of rock and release, on average, about the same amount of energy as a gallon of milk falling off a kitchen counter.”
It’s unclear why the USGS researchers chose to loop naturally occurring earthquakes in with induced seismicity. This only serves to increase fear and alarm in the public, when our collective focus should be on identifying solutions where induced seismicity is actually occurring.
It is also unfortunate that the report failed to quantify the number of wells that are actually linked to seismicity. Granted, such an accounting may have been beyond the scope of the research, but the report more or less glosses over this very important detail.
That said, any credible scientific body of research on the subject of induced seismicity will help us further quantify the risk moving forward, and ultimately develop solutions. The good news, as Bill Ellsworth with the USGS noted, is that the risk is manageable. As researchers continue to explore site-specific conditions that explain why one injection activity may induce seismicity while thousands of similar activities won’t, research from the USGS and other institutions that have benefitted from the industry’s active investment in solving this issue will hopefully provide the kinds of solutions that the public demands.