Five Things to Know About a New Stanford Oklahoma Earthquake Study

Today, Stanford University geophysicists F. Rall Walsh III and Mark Zoback released a new study in the journal Science Advances entitled, “Oklahoma’s Recent Earthquakes and Saltwater Disposal.”

The researchers claim the increase in seismic activity has coincided with a dramatic increase in volumes of disposal of salty wastewater into the Arbuckle formation, a 7,000 foot deep, sedimentary formation under Oklahoma. They believe the formation is in hydraulic communication with the crystalline basement, where almost all of the earthquakes are occurring.

Everyone can agree that no matter what is causing the spike of seismic activity in Oklahoma over the past five years, it’s an issue that all parties want to see addressed. While this study is certainly a significant contribution to scientific knowledge – and much of the data and analysis provided will help us better understand induced seismicity in Oklahoma – the researchers’ focus on wastewater volumes and comparative lack of downhole pressure analysis (among other factors) does raise a number of questions to consider.

Here are five key facts to know while reviewing this new report:

Fact #1: Produced water volumes much higher in the 1980s, yet there was minimal seismic activity

Walsh et al. suggest an increase in injected volumes in recent years is the determining factor for Oklahoma’s increased seismicity.  But the researchers’ data only go as far back as 1997.

As the chart below shows (using preliminary data provided by the Oklahoma Geological Survey), produced water volumes were roughly 30 percent higher in Oklahoma during the 1980s than they were in 2011, yet there was minimal seismic activity at the time.

Oklahoma Quakes

Compare this data going back to the 1980s with the data in the Stanford study, which only goes back to 1997:


As the report explains,

“As can be seen in figure 2, the aggregate monthly injection volume in the state gradually double from about 80 million barrels/month in 1997 to about 160 million barrels/month in 2013.”

But it does not include the fact that volumes were about 30 percent higher in the 1980s.

Of course, the researchers focus specifically on the increases in wastewater injection in the Arbuckle formation to come to their conclusions.  Their data certainly show an increase in disposal volumes coinciding with an increase in seismicity.  However, in order to gain a thorough picture as to whether the volumes themselves are the cause of the seismicity, the data would need to stretch back to the 1980s to determine if injection into disposal wells was also higher in the Arbuckle formation, as it was across the entire state.

While we know that wastewater injection was certainly taking place in the Arbuckle formation in the 1980s, neither the OGS data nor the Stanford researchers’ data for the Arbuckle go back far enough determine if there was an increase or decrease.  But with actual volumes of wastewater throughout the state being so much higher in the 1980s, understanding how much was going into Arbuckle at that time is an important part of the puzzle, which is not addressed in the study.

To be clear, this isn’t about denying a link between wastewater injection in Oklahoma and earthquakes. But it illustrates the fact that data during times of higher injection volumes statewide should be addressed to gain a clearer picture.

Fact #2: Researchers focus almost entirely on volume as the trigger for seismicity while glossing over other well-established factors 

The press release states,

“Stanford geophysicists have identified the triggering mechanism responsible for the recent spike of earthquakes in parts of Oklahoma-a crucial first step in eventually stopping them.

In a new study published in the June 19 issue of the journal Science Advances, Professor Mark Zoback and PhD student Rall Walsh show that the state’s rising number of earthquakes coincided with dramatic increases the disposal of salty wastewater into the Arbuckle formation, a 7,000-foot-deep, sedimentary formation under Oklahoma.”

In other words, the researchers claim to have identified the triggering mechanism for seismicity: high volume injection.

But it’s important to note Southwestern Oklahoma has high injection volumes but few if any felt seismic events. The same can be said for western and northeast Oklahoma.

It’s 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.”

That’s also precisely why 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.  A recent USGS report emphasizes this fact:

“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)

Also important is that 80 percent of Oklahoma is within nine miles of an injection well, yet 80 percent of the state is not experiencing induced seismicity. On that point, the researchers do admit,

“With thousands of injection wells in the state, it is likely that some naturally-occurring earthquakes would occur in the vicinity of disposal wells.”

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 #3: Fracking not to blame

Walsh et al.’s report makes it crystal clear that the fracking process is not to blame for the spike in seismicity in Oklahoma. Zoback had the following to say in press release accompanying the report:

“What we’ve learned in this study is that the fluid injection responsible for most of the recent quakes in Oklahoma is due to production and subsequent injection of massive amounts of wastewater, and is unrelated to hydraulic fracturing.” (emphasis added)

Fracking isn’t even discussed at length until the sixth page of the report, and the report points out that fracking fluids are a very small component of wastewater disposal:

“… hydraulic fracturing flowback water comprises an extremely small fraction of the injection into the SWD (salt water disposal) wells… In other words, nearly all the water being injected into SWD wells in these areas is produced water.”

Interestingly, much of the wastewater in central Oklahoma has nothing to do with hydraulic fracturing at all – a fact alluded to in the press release accompanying their report:

“Because the pair were also able to review data about the total amount of wastewater injected at wells, as well as the total amount of hydraulic fracturing happening in each study area, they were able to conclude that the bulk of the injected water was produced water generated using conventional oil extraction techniques, not during hydraulic fracturing.”

A recent lead story in Seismological Research Letters talked on this underreported fact as well.

“Salt water is produced at virtually all oil wells, whether the wells were hydraulically fractured or not. In fact, hydraulic fracturing is not used in the Hunton Dewatering Play in central Oklahoma, yet it is one of the largest producers of salt water in the United States.”

The USGS recently made similar comments.

… In some parts of Oklahoma where very high volumes of wastewater are injected, no hydraulic fracturing is occurring at all, so the wastewater is purely saltwater that comes up with oil in the extraction process.” (emphasis added)

Some media outlets have perpetuated the myth that there would be no need for wastewater disposal if hydraulic fracturing was not used. But the fact is that wastewater is produced in nearly every oil and gas well, not just wells that have been fracked. No wonder Zoback recently had the following comment in the Dallas Morning News:

“I really think bans on hydraulic fracturing are political statements rather than risk management tools.”

Fact #4: More than 99 percent of injection wells operate without seismicity

With the focus of the report being on volumes injected, the researchers did not address the very important issue of how many injection wells could be linked to seismicity.

Numerous experts have found that 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 explained just a few weeks ago, “Most injection wells do not trigger felt earthquakes.”

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)

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.

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.

Energy In Depth released an analysis of North Texas earthquakes, which looks at data from the Texas Railroad Commission of Texas 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.

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 #5: Industry, scientists and regulators are collaborating to manage the risk

Like most recent reputable studies, Walsh et al. calls for increased collaboration between industry, scientists, and regulators, and that’s exactly what has been happening in recent years.

In Oklahoma, the Corporation Commission (OCC) has increased its scrutiny for new injection wells in seismically active areas and strengthened its oversight.  The onus is now on producers to prove they’re not injecting into fault-riddled bedrock. 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. As many as 20 permit apps for injection wells in Oklahoma were never filed because they were in red-light zones and 25 app permits were rejected.

State First has also 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 (this study), the University of Oklahoma, and Southern Methodist University (among others).

The industry has also helped to secure funding for additional seismic monitoring throughout Oklahoma. Oklahoma currently has 20 permanent seismic monitors and 15 temporary monitors, which means the state has one of the most robust seismic monitoring systems in the U.S.  OGS seismologist Amberlee Darold explained that industry has in-depth information on the thousands of faults in Oklahoma that have proved invaluable:

“They are giving us their proprietary information to help the state as a whole understand the faults.”

OCC Oil and Gas Conservation Division Director Tim Baker said industry has been cooperative and has recognized the risks associated with injecting in elevated-risk, basement rock areas.

“Industry understands that risk (of injecting into the basement rock) and they are voluntarily shutting their (injection) wells in and plugging their wells back… just to ensure their well is not contributing to any type of risk of induced seismicity.”

Steps have already been taken to address disposal in the Arbuckle group. In March 2014, the OCC voted unanimously to adopt new rules requiring additional data monitoring and reporting of pressure for disposal wells in the Arbuckle formation and those rules went into effect in September. Pressure and volumes in Arbuckle formation “Areas of Interest” must now be recorded daily and reported weekly to the OCC. The new rules also subject wells injecting 20,000 or more barrels a day to be subject to mechanical integrity tests and all injection applications must undergo seismic review. The “Area of Interest” applies to 347 of 900 Arbuckle injection wells.


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