New research suggests that fracking, even with liquid carbon dioxide, causes small tremors not previously clearly attributed to the process. While CO2 fracking can sequester carbon and benefit the environment, both CO2 fracking and water-based fracking can lead to these tremors with the potential for larger damaging earthquakes.
New research has confirmed that fracking is responsible for previously unexplained slow, small earthquakes or tremors. Aftershocks are caused by the same processes that could cause large, destructive earthquakes.
Fracking involves forcibly injecting fluids below the earth’s surface to extract oil and natural gas. Although commonly performed using wastewater, this particular investigation focused on the results when liquid carbon dioxide is used. This method drives the carbon deep into the ground, preventing it from contributing to trapping atmospheric heat.
According to some estimatesCarbon dioxide fracking could save as much carbon as one billion solar panels annually. It is much better for the environment to frack with liquid CO2 than with wastewater, which does not keep carbon out of the atmosphere.
“Because this study examines a process that sequesters carbon underground, it may have positive implications for sustainability and climate science,” said Abhijit Ghosh, associate professor of geophysics at UC Riverside and co-author of the study in the journal. Science.
Because carbon dioxide is liquid, Ghosh said the results of this study almost certainly apply to water fracking. Both are likely to cause tremors.
Regular earthquakes and tremors appear differently on a seismograph. Large shocks cause sharp tremors with high pulse amplitude. The tremors are more subtle, slowly rising above the background noise with much smaller amplitude and then slowly falling.
A shale gas drilling (fracking) rig near Alvarado, Texas. Credit: Loadmaster (David R. Tribble)
“We are pleased to now be able to use these tremors to monitor the movement of fluids from fracking and to monitor the movement of faults resulting from fluid injection,” Ghosh said.
There used to be a debate among seismologists about the source of the tremors. While some papers claimed that the tremor signals came from large earthquakes that occurred thousands of kilometers away, others believed that it could have been noise generated by human activity, such as the movement of trains or industrial machinery.
“Seismometers are not smart. You could drive a truck nearby, or kick it with your foot, and it would pick up the vibrations,” Ghosh said. “That’s why we didn’t know for sure for a while whether the signals were related to the fluid injections.”
To determine their origin, the researchers used seismometers installed around a fracking site in Wellington, Kansas. The data covered the entire six-month fracking injection period, as well as the month before and one month after the injections.
After removing the background noise, the team showed that the remaining signals were generated underground and appeared only during fluid injection. “We did not detect tremors before or after the injections, suggesting that the tremors are related,” Ghosh said.
It has been known for some time that fracking can cause larger earthquakes. To keep fractures from going underground and creating them or tremors, one option would be to stop fracking. Because that’s unlikely, Ghosh says it’s important to monitor these activities to understand how rocks are deformed by them and to track the movement of fluids after injection.
Modeling experiments can be and are conducted to help companies determine fluid injection pressures that should not be exceeded. Staying within these limits helps ensure that fluids do not migrate to large faults underground, causing damaging seismic activity. However, not all faults are mapped.
“We can only model this type of experiment if we know there is an error. It is possible that there are bugs that we are not aware of and in such cases we cannot predict what will happen,” said Ghosh.
Reference: “Tremor signals during fluid injection are generated by fault slip” by Shankho Niyogi, Abhijit Ghosh, Abhash Kumar, and Richard W. Hammack, 3 Aug 2023, Science.
DOI: 10.1126/science.adh1331
