EARTHQUAKES IN OKLAHOMA

FAQs

The Oklahoma Geological Survey’s FAQ page can be accessed here.


 

6 Myths and Misconceptions

What you do and don’t know about induced seismicity

Provided by the United States Geological Survey (USGS) http://earthquake.usgs.gov/research/induced/myths.php

Fact 1: Fracking is NOT causing most of the induced earthquakes. Wastewater disposal is the primary cause of the recent increase in earthquakes in the central United States.

Wastewater disposal wells typically operate for longer durations and inject much more fluid than hydraulic fracturing, making them more likely to induce earthquakes. Enhanced oil recovery injects fluid into rock layers where oil and gas have already been extracted, while wastewater injection often occurs in never-before-touched rocks. Therefore, wastewater injection can raise pressure levels more than enhanced oil recovery, and thus increases the likelihood of induced earthquakes.

Fact 2: Not all wastewater injection wells induce earthquakes.

Most injection wells are not associated with felt earthquakes. 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.

Fact 3: Wastewater is produced at all oil wells, not just hydraulic fracturing sites.

Most wastewater currently disposed of across the nation is generated and produced in the process of oil and gas extraction. As discussed above, saltwater is produced as a byproduct during the extraction process. This wastewater is found at nearly every oil and gas extraction well.

The other main constituent of wastewater is leftover hydraulic fracturing fluid. Once hydraulic fracturing is completed, drilling engineers extract the fluids that are remaining in the well. Some of this recovered hydraulic fracturing fluid is used in subsequent fracking operations, while some of it is disposed of in deep wells.

Fact 4: The content of the wastewater injected in disposal wells is highly variable.

In many locations, wastewater has little or nothing to do with hydraulic fracturing. In Oklahoma, less than 10% of the water injected into wastewater disposal wells is used hydraulic fracturing fluid. Most of the wastewater in Oklahoma is saltwater that comes up along with oil during the extraction process.

In contrast, the fluid disposed of near earthquake sequences that occurred in Youngstown, Ohio, and Guy, Arkansas, consisted largely of spent hydraulic fracturing fluid.

Fact 5: Induced seismicity can occur at significant distances from injection wells and at different depths.

Seismicity can be induced at distances of 10 miles or more away from the injection point and at significantly greater depths than the injection point.

Fact 6: Wells not requiring surface pressure to inject wastewater can still induce earthquakes.

Wells where you can pour fluid down the well without added pressure at the wellhead still increase the fluid pressure within the formation and thus can induce earthquakes.


Separating Fact from Fiction on Oklahoma Earthquakes

by R. Kress

Click here for a link to the article.

The proliferation of Oklahoma earthquakes rightfully has regulators, lawmakers, residents and geologists concerned, and there’s little doubt that wastewater injection from fracking operations is playing a role in the state’s increased seismic activity. The State of Oklahoma is now telling oil and gas companies to reduce their wastewater injections at dozens of disposal sites, but a larger-scale clampdown remains to be seen. As legislators debate whether or not to impose a tax on injected fluids per barrel that would compensate residents who’ve seen earthquake-related damages, misconceptions remain about the cause, the scope and the solutions for this problem.

Myth: Oklahoma is now the earthquake capital of the United States.

While it’s a catchy tagline—most recently employed by the Associated Press—geologists aren’t in agreement. Dr. Jeremy Boak, Director of the Oklahoma Geological Survey tells the Fuse to note that Alaska, part of the continental (if not contiguous) U.S. has many more earthquakes than Oklahoma. California, while seeing fewer earthquakes, experiences much stronger ones—Boak estimates that California released ten times the amount of seismic energy that Oklahoma did in 2015.

“Oklahoma is the small earthquake capital of the U.S.,” Boak clarifies. “We have a preponderance of smaller earthquakes and they appear to be a feature of this induced seismicity.”

Myth: Oklahoma’s earthquakes are caused by fracking.

Experts say there is an important distinction to be made between saying that hydraulic fracking causes earthquakes and saying that the disposal of fracking wastewater causes earthquakes.

“There are a very small number of actual ‘frack quakes’—earthquakes that happen during or immediately after a frack job. But these are not that kind,” cautions Boak.

Instead, he explains that the oil and gas being produced from fracking comes to the surface along with large volumes of formation water—usually ancient ocean water. At a facility on the surface, operators typically separate the water from the oil and gas so the latter two can be brought to market. The remaining water, however, has a very high salt content and may also be contaminated by heavy metals or the oil and gas itself after centuries or even millennia sitting in the rock formation. That water must then be disposed of.

In Oklahoma, the oil and gas is being extracted from wells with a high water to hydrocarbon ratio. Boak estimates that for every barrel of oil that can be produced, operators are left with 10 to 15 barrels of wastewater. That leaves a big disposal job that continues through the life of the well, long after drilling and hydraulic fracturing are complete. For years, in Oklahoma, operators had been injecting that wastewater into the Arbuckle Group, which is the deepest sedimentary rock unit in most of Oklahoma. Over time, the steadily increasing volume raised the pressure in the Arbuckle and in the deep basement, where most of the active faults lie, causing earthquakes.

“The Arbuckle Group took a lot of water for a long time until we put so much in that it started causing earthquakes,” Boak explains. “It’s not a lot of flow into the basement but it’s transmitting a pressure wave. And the slight increase in pressure is enough to make it easier to move.”

Boak compares the shift to a puck on an air hockey table. Without the air flow, the puck barely moves. With just a small change in the air below it, however, it slides with ease.

While it is a misconception that fracking itself causes earthquakes, it is true that without the widespread use of the technique, the eventual induced earthquakes caused by produced water disposal would be avoided altogether. Boak, however, says that this is a “specious argument.”

“Yes, it’s true. If you shut down all fracking, you wouldn’t have the earthquake problem. But you would then shut in a whole lot of places that don’t have the earthquake problem, and you’d lose huge amounts of production,” Boak says, noting that the Bakken formation is also hydraulically fractured, but requires less wastewater disposal, has seen few to no induced earthquakes.

Myth: Without induced earthquakes, Oklahoma would have no seismic activity.

Unlike California or Japan or Hawaii, Oklahoma does not come to mind first as an area of natural seismic activity. However, this is a popular misconception.

“Geologists have identified a fault in Southern Oklahoma that ruptured in prehistoric times—more than 1000 years ago, but not much more. It produced an earthquake with a magnitude around 7.0,” explains William Ellsworth, a professor with the Stanford Center for Induced and Triggered Seismicity. “A recurrence of an earthquake that size would be a very serious event and we know that in parts of [Oklahoma], there are faults capable of producing large earthquakes.”

Both Boak and Ellsworth note that an increase in the number of small earthquakes also boosts the probability of a larger earthquake occurring—and it doesn’t seem to matter if those small earthquakes are induced or natural. Regardless, Ellsworth suggests that Oklahoma residents educate themselves in earthquake preparedness.

“Not knowing the very simple things can have very tragic consequences,” Ellsworth says. “Running out of a building in an earthquake in Oklahoma is the wrong thing to do. Public education could play a very big role in protecting [people] in a very strong earthquake.”

Myth: The straightforward solution is to halt fracking and wastewater disposal altogether.

Even if state regulators were able to put a total end to all wastewater disposal operations today, the quakes might continue all the same.

“If you shut it in completely, right away, you might get more earthquakes,” Boak notes. “Because then, you’ll get a negative pressure pulse moving out in these areas. Some of these earthquakes we’re now seeing are in areas where we’ve actually shut in injection. That might be one type of response.”

Ellsworth also notes that a seismic hazard will remain, even with positive changes to industry practices.

“From an earth sciences perspective, finding ways that the fluids can be disposed of without raising pressure in the basement over a large region is the goal,” Ellsworth says. “We don’t know how the hazard will evolve with time. Even if all the injections stopped tomorrow, the pressure is already underground and it would take some time to dissipate.”


 

How many earthquakes has Oklahoma experienced in the last few years?

Oklahoma experienced 907 magnitude 3+ earthquakes in 2015, 585 magnitude 3+ earthquakes in 2014 and 109 magnitude 3+ earthquakes in 2013. We typically discuss numbers of earthquakes based on magnitude 3+ since these earthquake events are able to felt by most people.

What is being done in response to the growing number of earthquakes in Oklahoma?

In September 2014, Governor Fallin tasked Secretary of Energy and Environment Michael J. Teague to convene the Coordinating Council on Seismic Activity.  The Coordinating Council meets regularly to share data, studies, developments and proposed actions related to Oklahoma’s earthquakes.

Individual state agencies are at the forefront of the earthquake response.  For example, the Oklahoma Corporation Commission, the state’s oil and gas regulatory agency, has instituted rules and directives aimed at mitigating seismicity risks related to wastewater disposal wells.

Other information about specific state agency actions related to earthquakes can be found in the “What We Are Doing” and “News” tabs at the top of this website.

What is the difference between a natural earthquake and a triggered earthquake?

Naturally occurring earthquakes happen as a result of natural movements along faults in the earth’s crust.  Triggered earthquakes happen where there is a naturally occurring fault that has the potential to slip and is triggered by some other event, such as a man-made activity or even another earthquake.

Most seismologists, including the Oklahoma Geological Survey, agree that the primary suspected source of triggered seismicity is not from hydraulic fracturing but from the subsequent disposal of produced water.

How is produced water different than wastewater from a hydraulic fracturing operation?

Produced water is naturally occurring water within the Earth that co-exists with oil and gas under the ground.  As oil and gas is extracted from the ground, the produced water is separated and often injected deep beneath the surface in wells designed to protect groundwater resources.  Hydraulic fracturing, extraction of oil and gas and the disposal of produced water are distinct events in the oil and gas production process.  The amount of produced water resulting from oil and gas production is often much more than the amount of wastewater resulting from a hydraulic fracturing operation.

What are wastewater disposal or injection wells?

Disposal wells (sometimes referred to as injection wells) are used to dispose produced water associated with the production of oil and natural gas.  Disposal wells associated with oil and gas operations are known as Class II wells.  The Oklahoma Corporation Commission administers the permitting and use of Class II disposal wells.