Predicting Earthquake Hazards From Wastewater Injection

ASU-led geoscientists develop a method to forecast seismic hazards caused by the disposal of wastewater after oil and gas production.   (Image: via   pixabay  /  CC0 1.0)
ASU-led geoscientists develop a method to forecast seismic hazards caused by the disposal of wastewater after oil and gas production. (Image: via pixabay / CC0 1.0)

A byproduct of oil and gas production is a large quantity of toxic wastewater called brine. Well-drillers dispose of brine by injecting it into deep rock formations, where its injection can cause earthquakes. Most quakes are relatively small, but some of them have been large and damaging.

Yet predicting the amount of seismic activity from wastewater injection is difficult because it involves numerous variables. These include the quantity of brine injected, how easily brine can move through the rock, the presence of existing geological faults, and the regional stresses on those faults.

Wells drilled into Oklahoma's Arbuckle formation inject wastewater (1) which then disperses through the rock. As it spreads, the wastewater can trigger earthquakes in fault zones (2), but their size depends on the amount injected and the rock's properties. The new model can predict quake probabilities by the quantity of wastewater injected. (Image: Guang Zhai/Manoochehr Shirzaei/ASU)

Wells drilled into Oklahoma’s Arbuckle formation inject wastewater (1), which then disperses through the rock. As it spreads, the wastewater can trigger earthquakes in fault zones (2), but their size depends on the amount injected and the rock’s properties. The new model can predict quake probabilities by the quantity of wastewater injected. (Image: Guang Zhai / Manoochehr Shirzaei / ASU)

Now a team of Arizona State University-led geoscientists, working under a Department of Energy grant, has developed a method to predict seismic activity from wastewater disposal. The team’s study area is in Oklahoma, a state where much fracking activity has been carried out with a lot of wastewater injection and where there have been several induced earthquakes that have produced damage.

The model shows earthquake probability curves for central Oklahoma increasing to 2015 due to brine injection. After injection is reduced and assumed to end in 2017, brine continues to diffuse in the rock, and the curves retreat to background levels. The new model allows operators to compute quake probability for various injection scenarios, maximizing injection while minimizing hazards. (Image: Guang Zhai/ASU)

The model shows earthquake probability curves for central Oklahoma increasing to 2015 due to brine injection. After injection is reduced and assumed to end in 2017, brine continues to diffuse in the rock, and the curves retreat to background levels. The new model allows operators to compute quake probability for various injection scenarios, maximizing injection while minimizing hazards.
(Image: Guang Zhai / ASU)

The team’s paper appears in the Proceedings of the National Academy of Sciences. Guang Zhai, a postdoctoral research scientist in ASU’s School of Earth and Space Exploration and a visiting assistant researcher at the University of California, Berkeley, said:

Zhai is lead author for the paper, and the other scientists are Manoochehr Shirzaei, associate professor at the school, plus Michael Manga of UC Berkeley and Xiaowei Chen of the University of Oklahoma. Shirzaei said:

Back to basics

To address the problem, his team went back to basics, looking at how varying amounts of injected brine perturbed the crustal stresses and how these lead to earthquakes on a given fault. Zhai said:

The key was building a physics-based model that combined the rock’s ability to transport injected brine and the rock’s elastic response to fluid pressure. Shirzaei explained:

He added that to make the scenario realistic, the model also includes the mechanical properties of the rocks in Oklahoma. The result was that the model successfully predicted changes in the crustal stress that come from brine injection. For the final step, Shirzaei said:

The team found that the physics-based framework does a good job of reproducing the distribution of actual earthquakes by frequency, magnitude, and time. Zhai said:

Making Production Safer

While wastewater injection can cause earthquakes, all major oil and gas production creates a large amount of wastewater that needs to be disposed of, and injection is the method the industry uses. Shirzaei said:

Knowing the volume of brine to be injected and the location of the disposal well, authorities can estimate the probability that an earthquake of a given size will result. Such probabilities can be used for short-term earthquake hazard assessment.

Alternatively, the team says, given the probability that an earthquake of a certain size will happen, oil and gas operators can manage the injected brine volume to keep the probability of large earthquakes below a chosen value. Zhai added that the end result

Provided by: Arizona State University [Note: Materials may be edited for content and length.]

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