Earthquakes in Oklahoma and Kansas had been on the rise because of the injection of wastewater—a byproduct of oil and gas operations—before regulations started limiting injections. Now, a new model developed by Stanford University researchers incorporates earthquake physics and the Earth’s hydrogeologic response to wastewater injection to forecast a decrease in man-made earthquakes in Oklahoma and Kansas through 2020.
The model is based on publicly available data on wastewater injection into the Arbuckle formation, a nearly 7,000-ft-deep sedimentary formation underlying north-central Oklahoma and southern Kansas. Assuming wastewater injection from oil and gas operations continues at its current rate, researchers mapped the likelihood that the region will experience future earthquakes. The research appears in the journal Nature Communications.
“We’ve created a detailed model that allows regulators to know where most of the problems are likely to occur,” said coauthor Mark Zoback, the Benjamin M. Page Professor of Geophysics at Stanford’s School of Earth, Energy, and Environmental Sciences (Stanford Earth). “This can be used in Oklahoma, or elsewhere, to provide a scientific basis for regulatory action.”
Oil and gas operations often produce large volumes of salty water that they dispose of by injecting it deep underground to protect water in aquifers near the surface used for drinking, livestock, and irrigation.
Fluid injected into the Arbuckle formation increases pressure that spreads over a large area. This pressure is problematic because it can affect large faults nearby that are already under stress from tectonic processes. These faults are capable of producing widely felt and potentially damaging earthquakes, if reached by the pressure increase caused by injection.
The same pressure increase in different areas can cause up to 100 times the number of earthquakes, according to lead author Cornelius Langenbruch, a postdoctoral researcher at Stanford Earth. The earthquakes are not necessarily concentrated in areas where the pressure change is highest. In order to understand where earthquakes will or will not occur on a local scale, the new model evaluates the pressure increase in the context of the area’s vulnerable, pre-existing faults.
“It was surprising for me to see that the local susceptibility to earthquakes fluctuates by such a large amount,” Langenbruch said. “The example of Oklahoma shows that the key to managing seismic hazards related to these man-made, induced earthquakes is managing how much and where the wastewater is injected.”
Read the full story here.
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