Residents in Oklahoma and Kansas have become accustomed to a new reality: earthquakes. They range from so small they’re only detectable by scientific instruments, to so powerful they can crumble brick walls.
Justin Rubinstein, of the United States Geological Survey, has been studying the tremors in this region and determining what’s causing them. The California-based geophysicist sat down with KMUW's Sean Sandefur.
Sandefur: There have been hundreds of earthquakes recorded in Kansas over the past few years, and I understand that some people think it’s caused by fracking, or drilling deeper into the earth. But it’s actually a bi-product of that process and other exploration, is that right?
Rubinstein: That’s right. What we’re really seeing is that wastewater disposal is responsible for the earthquakes that we’re seeing here in Kansas and Oklahoma. I should clarify what I mean by wastewater. Basically, any waste product from the oil and gas process. Now, what we’re actually seeing as wastewater is what we call produced water. When you extract oil or gas, there’s saltwater trapped in these same formations. You pull up this saltwater whether you like it or not. This needs to be disposed of. If it can’t be cleaned up for disposal on the surface, oil and gas companies will drill deeper wells and inject the fluids into those wells.
Most of the time when we inject it, we never hear from it again. But every once and awhile, the fluids can find their way to a fault and raise the fluid pressure, more or less prying that fault open. You might think of it as lubricating that fault, making it more likely to slip. And so that’s that we believe is happening in Kansas [and] in Oklahoma.
When you present your findings, these earthquakes are known as induced seismicity. What does that term mean?
So, what I mean when I say 'induced seismicity' is any earthquake that was caused by human activity. And there’s a long history of induced seismicity going back to the late 1800s—mining-related seismicity. There’s also seismicity related to the filling of reservoirs, there’s seismicity related to oil and gas production, and there’s also seismicity related to the injection of fluids that’s a part of oil and gas production and other industrial processes as well.
When an earthquake does occur, how do scientists know that it was caused by human activity? I would imagine that’s difficult.
Distinguishing between natural and induced seismicity is very challenging, and there is no easy way to do it. Everybody asks us for a way to do this, and I’d love to come up with a way to do that. But, really, the way we identify induced earthquakes [is] we have to individually study the earthquake sequence, look at what the operational parameters are in the area. If we need to put together some numerical models to understand where the fluids are flowing, what the pressure changes are in these potential faults, we do that sort of thing.
Now, it’s much easier here in the central United States where there is a very low background earthquake rate. Going to California, where I live, it’s a much more challenging problem because we have a very high background earthquake rate so distinguishing between induced earthquakes and natural earthquakes becomes much more challenging. Whereas, if you’re here in Kansas, seeing a big increase in seismicity is going to start you down that road immediately, whereas in California, the assumption is that it’s natural.
Kansas and Oklahoma have put some regulations in place where this wastewater injection is happening, like limiting wastewater injection in certain counties, even shutting down wells in some places. Are these efforts working?
Kansas really, to some degree, has gotten ahead of the problem and has been very proactive in trying to reduce the seismicity. And I think Oklahoma reacted a little bit more slowly, but we are seeing a drop in the seismicity.
[View the Kansas Geological Survey's interactive earthquake map here.]
You’ve been doing presentations about the link between wastewater injection and earthquakes. What has the response been? I would imagine that this could be a somewhat politically charged issue.
The reactions are pretty varied, in general. I think people believe it. I guess I would actually couch it in sort of, how we’ve gotten reactions from industry. You know, it’s certainly not in their interest to cause earthquakes. I think that even a few years ago in meetings with industry there are a lot of parts of industry that would deny that induced earthquakes exist. And now I don’t feel like any credible member of industry denies that induced earthquakes can occur and that fluid injection can cause these earthquakes. They may deny that they specifically are causing earthquakes, but I think that industry is really on board that these earthquakes are being caused by fluid injection.
And how does that affect your work now that they are on board?
It’s actually, I would say, a little bit fortunate for those of us who are studying this from an academic standpoint in that they are now really invested in actually working with us to understand the problem. Because if our science and their understanding of their reservoirs can help them develop methods to prevent these earthquakes, it’s in everybody’s interest.
So, if oil and gas companies are starting to kind of own up to this, are there lawsuits occurring from people whose houses or property have been damaged from earthquakes?
Well, I’m not an attorney, but what I can tell you is that there are lawsuits pending in both Oklahoma and Arkansas against operators, stating that the damage caused by these earthquakes was due to the oil and gas activities. As far as I know, none of these lawsuits have been resolved, but these lawsuits are ongoing so it will be interesting to see how this plays out.”
One last thing I want to ask is the long-term effect. Even if this wastewater injection stops, can there be lingering issues?
There’s no clear answer, is the short answer. In some areas where we’ve seen termination of injection, we’ve seen the seismicity disappear within weeks. In other areas, the seismicity has lasted for years. And really, the classic case of injection-induced seismicity [is] at the Rocky Mountain Arsenal outside of Denver, earthquakes persisted for over a decade after injection terminated. And in fact, the largest earthquake to occur, which was a magnitude 4.9 there, happened a year after injection stopped. So, just stopping injection isn’t a quick-fix solution. Most of the time, it really does appear to dramatically reduce earthquake rates. But it doesn’t always fix the problem immediately.
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