Sweeping Assumptions Underscore New CU-Boulder Seismicity Study
A new report led by researchers at University of Colorado Boulder titled, “High-rate injection is associated with the increase in U.S. mid-continent seismicity” proclaims decisively “We find the entire increase in earthquake rate is associated with fluid injection wells” (emphasis added).
While any report on seismicity should be taken seriously at a time when producers, researchers and regulators are identifying best practices, it is also important to note that there are a number of glaring flaws in this particular report that should be kept in mind while evaluating it.
Here are the four key facts to know:
Fact #1: Report assumes all earthquakes are induced by injection wells when the best available science shows it’s only a fraction of one percent of wells
The researchers’ conclusions rely on a number of sweeping assumptions regarding seismic data in the Central and Eastern US region (CEUS), including this:
“[W]e treated all earthquakes as potentially induced events to capture the most comprehensive data set of associated earthquakes and injection wells.” (emphasis added)
“We considered any earthquake within 15 km of an active injection well to be associated with that well.”
Painting with this broad brush, they come up with these numbers: “We find 18,757 injection wells (~10% of all wells) associated with earthquakes in the CEUS after filtering, mostly in the states of Oklahoma and Texas.”
Aside from the fact that making such blanket assumptions is less than scientifically robust, such large numbers have been debunked by the U.S. Geological Survey, which has studied this issue more than any other researchers to date. As the USGS said only a few weeks ago, “Most injection wells do not trigger felt earthquakes.” This is a point USGS has made in past studies as well: “Only a small fraction of these disposal wells have induced earthquakes that are large enough to be of concern to the public.” Even the EPA has noted that “very few” waste water wells induce seismicity.
Energy In Depth released an analysis of North Texas earthquakes, which looks at data from the Texas Railroad Commission as well as a number of recent peer reviewed studies and finds that 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.
Fact #2: Report claims only a single correlation to seismicity: injection rates
The researchers focus on only one condition that correlated with active disposal wells and measurable increases of seismic activity:
“Our analysis shows that injection rate is the most important well operation parameter affecting the likelihood of and induced seismic event in regions and basins potentially prone to induced seismicity.”
The researchers go on to state,
“At the scale of our study, no other operation parameter was found to have a strong influence on the likelihood of association with an earthquake.”
But it has long been established that one factor alone cannot be blamed solely for seismicity. As the USGS recently explained,
“A combination of many factors is necessary for injection to induce felt earthquakes. These include the injection rate and total volume injected; the presence of faults that are large enough to produce felt earthquakes; stresses that are large enough to produce earthquakes; and the presence of pathways for the fluid pressure to travel from the injection point to faults.”
The EPA has come to a similar conclusion: “The three key components behind injection-induced seismicity are (1) sufficient pressure buildup from disposal activities, (2) a Fault of Concern, and (3) a pathway allowing the increased pressure to communicate from the disposal well to the fault. All three components must be present to induce seismicity.”
As a recent compendium of seismicity reports conducted by the Southern Methodist University warns,
“The potential for seismic activity must be addressed based on downhole pressure, injected volumes, and location, including the orientation of certain faults. Peer-reviewed studies have consistently identified these variables as necessary to understand induced seismicity, and not to convey a blanket, one-size-fits-all approach that suggests geological or pressure conditions in any given area are analogous to operations in other parts of the country.”
Indeed, that is why the number of injection wells associated with seismicity is so small, as these rare factors have to be in place. While the researchers make a mention of these other elements, they still focus solely on high injection rates.
Induced seismicity needs to be addressed on a case-by-case basis, taking into consideration downhole pressure, volume, and location, including the orientation of certain faults. In other words, a blanket, one-size-fits-all approach is not an appropriate method of managing the risk.
Fact #3: There are straightforward ways to manage the risk
Notably, a recent USGS paper found that
“[T]he U.S. Geological Survey in collaboration with the University of Colorado, Oklahoma Geological Survey and Lawrence Berkeley National Laboratory, suggests that it is possible to reduce the hazard of induced seismicity through management of injection activities.”
As Bill Ellsworth of the USGS said recently,
“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.”
In order to mitigate the risk in 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 research shale fault data and other geological information. This kind of collaboration has happened in conjunction with major regulatory and operational changes in Texas and Oklahoma. In Oklahoma, the Corporation Commission (OCC) has increased its scrutiny for new injection wells in seismically active areas and strengthened its oversight.
Oklahoma 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 shut them down if their operation leads to seismicity.
The Texas Railroad Commission (RRC) unanimously adopted new Class II injection well rule amendments recently, which constitute the fourth significant updates to strengthen RRC’s oversight in the last three years. These rule amendments went into effect in November 2014.
In Colorado, a recent report from the Associated Press (AP) in Denver highlighted remediation efforts that are showing signs of success at a Weld County wastewater well believed to be associated with two seismic events that occurred last year. From the AP:
“The ground around a northern Colorado wastewater injection well has been relatively quiet for more than two months, offering hope that a 10-month string of more than 200 small earthquakes might have subsided.”
Those efforts included shutting the well down after the initial event and, according to the AP article:
“The bottom 450 feet of the 10,800-foot-deep well was plugged with cement last year, and that might be keeping the wastewater — a byproduct of oil and gas wells — from seeping into fractures and triggering earthquakes, researchers and regulators say.”
The AP reports that Stuart Ellsworth, engineering manager for the Oil and Gas Conservation Commission, and Anne Sheehan, a University of Colorado geology professor who has been monitoring the site, are “optimistic that shortening the well fixed the problem” and that similar efforts are underway in states like Oklahoma. Ellsworth told the AP:
“Well, I think it’s the answer,” Ellsworth said. “It was a remediation effort that reduced the risk of future events. At least that’s what it looks like.”
Fact #4: Hydraulic fracturing is not the link to seismic activity
The scientific consensus is that fracking rarely if ever induces felt seismic events. Hydraulic fracturing itself is not a credible risk for seismic activity and the USGS has made this point clear stating, “In the United States, fracking is not causing most of the induced earthquakes.”
A 2013 National Research Council study stated, “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.”
The EPA’s recent risk assessment of induced seismicity observed that hydraulic fracturing “has a low likelihood of inducing significant seismicity,” owing to its short duration and comparatively low “pressure footprint.”
The study’s lead author, Matthew Weingarten notes that, “broader-scale studies are needed to understand the phenomenon as a whole” when attempting to account for seismically induced events. While this study certainly adds to the growing body of literature on seismicity, it’s important to consider its sweeping assumptions and the fact that the researchers only looked at one piece of the puzzle.