Wastewater well depths linked to Oklahoma quakes

Adapted from Hincks et al., 2018, “Oklahoma’s induced seismicity strongly linked to wastewater injection depth”; Map: Lazaro Gamio / Axios

Scientists know that wastewater injection related to fracking for oil and gas can induce earthquakes. A new study published in Science Thursday found that the deeper these injections go towards a layer of rock called the crystalline basement, the more likely they are to cause earthquakes.

Why it matters: Oklahoma never used to experience many earthquakes, but since 2009, a number of damaging temblors have shaken the area. "State regulators could cut about in half the number of man-made quakes by restricting deep injections in the ground," study author Thea Hinck told the Associated Press.

What they did: The researchers developed a statistical model to evaluate the relationship between well operations (including the depth and rate of injection and the volume of liquids), the geology surrounding the wells, and earthquakes.

  • They evaluated all the Class II wells (used for oil and gas production) in Oklahoma and studied the seismic activity there.
  • There were 2,264 earthquakes of magnitude 3 or greater recorded in the state for the six-year-period of collected data.

What they found: Restricting injection depths to 200–500 meters above the basement level could reduce earthquakes by a factor of 1.2–2.8.

  • Location matters: "It turns out there are patches of higher and lower potential within the broader zone, and this affects how likely it is any particular well will be implicated in earthquake trigger," study author Thomas Gernon tells Axios.

Another perspective: U.S. Geological Survey's Art McGarr, a geophysicist not part of this study, told Axios most of the study's findings had been shown before. However, he says it's important to continue research.

"In Oklahoma, it is especially important to understand the causes of seismic activity because this source of hazard can be controlled, in contrast to natural seismicity, which is beyond human control," he says.

Editor's note: The headline was corrected to reflect the wells in the study were wastewater injection wells and not fracking wells.