Earthquake Potential of Hydraulic Fracturing Wells Not Related to Higher Injection Rates

18 April 2023–Analyzing hydraulic fracturing (HF) wells in Texas, Oklahoma, New Mexico and West Canada, researchers found that the average daily injection rates and the total injected volumes are not a crucial factor in determining whether a stimulation will trigger nearby earthquakes.

As Iason Grigoratos of ETH Zürich and colleagues discussed at the Seismological Society of America (SSA)’s 2023 Annual Meeting, this finding differs from the case of wastewater disposal wells, where higher injection rates have been associated with higher earthquake potential.

During hydraulic fracturing, well operators inject a pressurized liquid into a rock layer after drilling vertically and often horizontally through the rock. The liquid breaks apart —fractures– the rock and allows natural gas or petroleum to flow back through the well. This enables the extraction of oil and gas from previously unproductive shale formations. This process can induce felt seismicity of magnitude larger than 4, when undetected nearby faults are destabilized.

At the regional scale, Grigoratos said, geomechanical conditions are much more critical for triggering HF seismicity than the injection rate of the stimulation.

“Remember that HF injects fluids at tight shale formations of very low permeability,” he said. “Thus, increasing the injection rate is more likely to just cause more nearby fractures than significantly expand the spatial footprint of the stimulation. If the footprint is more or less fixed, so is the probability to encounter larger faults.”

On the other hand, wastewater disposal injects water into highly permeable formations, “leaving a much larger footprint in the underground stress field,” Grigoratos said. “The higher the injection rate, the larger the radius of this footprint. This is also why wastewater disposal can cause seismicity with a time-lag of many months or even years, while time-lags of more than a few days are not expected for HF.”

The researchers also found that less than 10% of the HF stimulations were responsible for all of the earthquakes linked to hydraulic fracturing across the basins in the study. Grigoratos added that “in certain basins, this tiny number of stimulations is responsible for a large percentage of the felt seismicity.”

Grigoratos said the findings do not support mitigation efforts for HF-induced earthquakes that are based on limiting the injection rate or total injected volume. On the other hand, he noted that “for wastewater disposal, limiting the injection rate and increasing the distance of the well from the basement reduces the likelihood of felt seismicity.”