Shaky Claims: Hydraulic Fracturing Is Causing Earthquakes


The term “fracking”—short for hydraulic fracturing—has become a buzzword throughout the United States. Proponents of the technology celebrate oil and natural gas production as a means of reducing energy prices and stimulating economic growth, while opponents of the well-completion technique voice environmental concerns, among them the fear hydraulic fracturing will usher in a new era of manmade earthquakes.

Since the technique was first used in 1947, hydraulic fracturing is thought to have caused only a handful of earthquakes large enough to be felt on the surface. The overwhelming majority of the wells where hydraulic fracturing is used are aseismic, meaning no earthquakes occur. The risks of hydraulic fracturing causing an earthquake are small compared with other human activities such as constructing dams, mining, and the use of deep underground injection wells to dispose of waste, which can cause comparatively larger earthquakes.

The largest earthquake risk associated with hydraulic fracturing stems from the use of injection wells to dispose of the wastewater generated during the fracturing process. Each hydraulically fractured well requires an average of two to four million gallons of water, and approximately 10 to 20 percent of this water flows back to the surface and is known as “flowback water.” This wastewater is generally either recycled or disposed of in injection wells. The best-available scientific evidence at this time suggests wastewater disposal – not the process of hydraulic fracturing itself – is the reason for increased seismic activity in some energy-producing areas of the country such as Kansas, Ohio, Oklahoma, and Texas.

Even well-respected news outlets such as Reuters have failed to distinguish between earthquakes caused by hydraulic fracturing (which are extremely rare) and those likely caused by wastewater disposal wells (which are more common) in the nuanced manner necessary to give readers the proper understanding of the issue. When headlines like “Small quake shakes Dallas area, stirring fracking critics” are published without discussion of the role played by the injection of wastewater into disposal wells, readers are left without the information they need to accurately weigh the costs and benefits of hydraulic fracturing as they pertain to earthquakes.

When Fault Li(n)es with Fracking

Most hydraulic fracturing operations have almost no detectable seismic impact. A recent study published in Seismological Research Letters notes the typical hydraulic fracturing operation accounts for seismic activity in the M3.0 to M0.0 range, about the same amount of energy generated when a gallon of milk falls from a kitchen counter. Additionally, because the moment magnitude scale is logarithmic, these microquakes are millions of times smaller than any seismicity than can be felt on the surface.

However, the study suggests hydraulic fracturing can lead to larger-than-normal seismic readings if oil and natural gas wells are drilled too close to existing fault lines, as was the case in Ohio in October 2013. The study found a series of earthquakes – the largest of them being an M2.2 – was generated when a well was drilled too close to an existing fault line. Although these quakes were larger than expected, likely due to the fault extending down to the basement rock, they were well below the threshold of what can be felt by people at the surface, a key reason why there were no reports anyone had felt these earthquakes.

One in a Million

Although no one in Ohio felt the earthquakes generated by hydraulic fracturing, incidents of the process generating earthquakes large enough to be felt at the surface have occurred.

Dr. Richard Davies, a professor of earth sciences at Durham University, compiled 198 published examples of manmade earthquakes from around the world registering at a magnitude greater or equal to 1.0 since 1929. Of these earthquakes, hydraulic fracturing was found to be responsible for only three quakes large enough to be felt on the surface: one in Canada, one in the United States, and one in Great Britain. The largest of these occurred in 2011 in the Horn River Basin of Canada and registered at M3.8, on the lower end of earthquakes that can be felt by people.

Because earthquakes must generally register near a magnitude 4.0 on the moment magnitude scale to be felt at the surface and between M5.5 and M6.0 to cause even slight damage to buildings, earthquakes caused by hydraulic fracturing are unlikely to have an effect on our everyday lives. These facts prompted Davies to make the following statement: “We have concluded that hydraulic fracturing is not a significant mechanism for inducing felt earthquakes. It is extremely unlikely that any of us will ever be able to feel an earthquake caused by fracking.”

Hydraulic fracturing has been used to stimulate more than one million oil and natural gas wells in the United States since 1947, according to estimates, making the incidence of earthquakes large enough to be felt on the surface caused by hydraulic fracturing in the United States one in one million.

Going Back to the (Injection) Well

Although hydraulic fracturing is not a significant mechanism for causing earthquakes large enough to be felt at the surface, the use of deep injection wells to dispose of wastewater can lead to earthquakes large enough to be felt. The first earthquakes caused by injection wells occurred in Colorado in 1965, after waste from a military complex was pumped for disposal into a hole 12,044 feet deep. These quakes eventually became known as the “Denver Earthquakes” and prompted further research on the link between waste disposal and manmade earthquakes.

The use of these wells to dispose of the wastewater produced by the hydraulic fracturing process has been linked to increased seismic activity in some energy-producing states, particularly Ohio, Oklahoma, and Texas. Furthermore, earthquakes caused by injection wells can be larger than those caused by hydraulic fracturing, potentially triggering earthquakes in M2.0 to M5.3 range.

Fortunately, according to a recent study in the journal Science, the risks associated with earthquakes triggered by the use of injection wells to dispose of fracking waste can be substantially reduced by avoiding wastewater disposal near major faults and the use of appropriate monitoring and mitigation strategies.

Oil-and-gas-producing states already have begun to incorporate protective rules and regulations limiting the volume of waste that can be pumped in a given well. Ohio regulators have enacted measures requiring the installation of pressure-monitoring systems to detect when wells have been over-pressurized and rules prohibiting drilling injection wells near fault lines and into basement rock formations. These rules and best practices give states a framework with which to reduce the amount of seismic activity associated with wastewater disposal.

Conclusion

The link between hydraulic fracturing and earthquakes has been largely overstated by environmental groups and often mischaracterized in news stories. Hydraulic fracturing has been shown to have caused felt earthquakes on only a handful of occasions worldwide since 1947. A greater risk of induced seismicity comes from the injection of wastewater from hydraulic fracturing operations, but these risks can be mitigated by encouraging the industry to recycle greater amounts of wastewater and enacting regulatory schemes to monitor and mitigate wells to prevent instances of manmade earthquakes.