Understanding how earthquakes occur near fracking wells can help scientists make energy production safer.
By Lena Beck, @LenaJLBeck
Citation: Beck, L., 2022, New fracking-generated earthquakes discovered, Temblor, http://doi.org/10.32858/temblor.247
Fracking is controversial for many reasons. Methane, a more potent greenhouse gas than carbon dioxide, can escape from fracked wells; groundwater can be contaminated; earthquakes can happen in places they historically have been rare, or in areas that are typically seismically inactive. The latter are a common result of underground fluid injection in places such as the midwestern United States and western Canada. Most of these quakes are small and go unnoticed by people on the ground, but some are widely felt.
Now, scientists have identified a new type of earthquake triggered by hydraulic fracking — the process by which fluid is injected into the Earth’s subsurface at a high pressure to release tight hydrocarbon reserves. Unlike other earthquakes caused by fracking operations, these events rupture more slowly and last longer. They may even provide clues as to how to make fracking more efficient and reduce seismic hazards in the future.
Injection-induced earthquakes
Earthquakes can occur when fracking fluid or wastewater is forced into small pore spaces in rock underground. The resulting increase in fluid pressure can cause faults to slip and generate an earthquake.
But in some cases, earthquakes resulting from hydraulic fracking have struck far from the injection site. In other places, the amount of fluid pumped below ground was insufficient to cause the magnitude of quakes observed. Until now, scientists have puzzled over how such induced quakes happen.
Earlier studies indicate the increase in pressure could also cause aseismic slip — slip not accompanied by an earthquake — in the broken up rocks close to Earth’s surface. This then transfers pressure to nearby faults, causing an earthquake. Unfortunately, the lack of measurable seismicity at the start of this process has made this phenomenon difficult to observe in the field.
In the new study, Hongyu Yu, a research scientist at the Pacific Geoscience Centre, and her colleagues installed eight seismic monitoring stations near a hydraulic fracking well in British Columbia, Canada. In the data collected, the group discovered a type of event that they call “hybrid-frequency waveform earthquakes,” or EHWs.
The researchers documented approximately 350 quakes in total, of which about 10% resembled EHWs. They suggest that these events are caused by a buildup of aseismic slip loading onto faults around an injection site. These earthquakes are identical to natural small magnitude quakes that occur in plate boundary fault transition zones, like volcanic areas.
Monitoring EHWs could make fracking safer
Induced seismicity has become more common in places such as the midwestern U.S. in the past couple decades. Induced seismicity “has been a relatively hot topic in the seismological community,” says David Eaton, a geophysicist at the University of Calgary’s Department of Geoscience who was not involved in the recent study. The observations noted in this study and the researchers’ new insights can improve our understanding of induced earthquakes, he says.
Yu says that further research on EHWs could help make the fracking process more efficient, and therefore less hazardous, going forward. By understanding how the subsurface reacts to hydraulic fracturing, scientists can suggest ways to modify the injection process to better anticipate seismic hazards and avoid damage.
But first, she thinks it’s important to collect more data from other locations. “EHWs should be observed in many places, not only in this case study,” Yu says, adding that more localized research could further the understanding of how EHWs could become useful in the future.
Further Reading
Eyre, T. S. et al. The role of aseismic slip in hydraulic fracturing–induced seismicity. Sci. adv. 5, eaav7172 (2019).
Bao, X. & Eaton, D. W. Fault activation by hydraulic fracturing in western Canada. Science 354, 1406–1409 (2016).