More than 800 earthquakes of magnitude 3.0 or greater have shaken the state of Oklahoma in 2015 alone, according to the Oklahoma Geological Survey. The rise in seismic activity is striking—in 2008, Oklahoma averaged roughly two such events per year.
By 2014, Oklahoma’s state geologists officially endorsed the U.S. Geological Survey’s conclusion: that the earthquakes were caused by the disposal of salty wastewater, a byproduct of oil and gas production. Once separated from the oil brought up from the ground, wastewater is disposed of through injection wells, drilled into what’s known as the Arbuckle sedimentary rock formation, which reaches more than a mile underground.
Todd Halihan is a professor of hydrogeology at Oklahoma State University who is frequently called on to explain the science behind the state’s earthquakes to the general public. As a result, he’s become a local celebrity of sorts. Halihan also sits on Oklahoma governor Mary Fallin’s Coordinating Council for Seismic Activity, an advisory body that includes scientists and representatives from the oil and gas industry.
“Fault Lines” spoke to Halihan about how Oklahoma became “the earthquake capital of the U.S.” An edited version of the conversation follows:
A lot of people seem to think fracking is causing Oklahoma’s earthquakes. Is that actually the case?
Fracking itself is just the process of cracking rock that's fine grain at depth and producing oil and gas. This has nothing to do with that. Fracking as a process is not causing the earthquakes.
What's causing these earthquakes is our oil fields have water in them. An oil well in many cases is just a saltwater well with some oil in it. So when we produce [oil] we need to do something with the water.
So back in the 1930's, the decision was to dispose of it at depth. And so we-injected about a mile down into the rocks. That's gone very well for a long time, but the volumes have increased with recent production. And now what we have is pressure hitting faults and making earthquakes.
How much water is being put underground?
The estimate I used before was it's roughly a billion barrels, or a couple billion barrels of water. And that doesn't really equate to people very much. So I did some calculations. There's a lake in the middle of Oklahoma City called Lake Hefner, and it's one of the reservoirs that a lot of people in the state have seen, or have boated on or fished on or these sorts of things. They know that lake. So it's about two of those lakes per year, going down into the ground. That's helped people understand. You're going to drain out an entire lake a couple times and shove it into a formation, a mile down.
So that's the issue: There's a billion barrels of unusable, super-salty water that is being injecting into the ground.
Right. And in the 1930's, the engineering question was, how do we make this water go away so that we can safely produce oil and gas? And so it was a water quality question: How do we not contaminate the surface? Everything was engineered for the surface. When you start having earthquakes, you have to engineer for the bottom of the wells.
And no one could have seen this coming, given Oklahoma’s geology?
Underneath the continents, you typically have granite. And if you drill down deep enough, you'll find it. And so those are the basement rocks, and that's about a mile down here. Injecting into those are a good way to make earthquakes. We've got good data to say that if you did that, you can make an earthquake. And so one of the first rules is don't do that.
So when they went down into the disposal zone, which is called the Arbuckle, if they were drilling along and then they hit the basement, well, now, instead of having carbonate rock come out, now granite came out. And they would call the [regulatory body] Oklahoma Corporation Commission and say, "Hey, you know, we hit the basement. Is that all right?" And they'd say, "Well, we're trying to protect the surface, so that's fine." You know, there's no problem going too deep. And so a lot of wells went and hit the basement.
Well, now we've gone to an environment of, "Wait a minute. We made earthquakes. What's rule one? Oh, don't do that. Oh, wait a minute, we were allowing that. Well, we didn't think we had a seismicity problem. Well, we didn't." So on a technical basis, they were meeting the objectives. But now there's new objectives, because there's a new problem.
Is it surprising that the regulatory body wouldn't know such a simple thing?
Well, they did. But they'd never had a problem with seismicity that they knew of. Starting in March, they put out a directive that everybody in the seismically active zone has to make sure they're not in basement. And so about 140 wells have been plugged back. Every time that's happened, it's been roughly a $200,000 operation. So that's totaled about $28 million. And that doesn't count the fact that you shut off your oil wells and lost that production, or that when you turn them back on, they may not produce the same, and you'll have to wait for that production to come back online.
So there's been millions of dollars spent because, you know, back in the day, we said, "Well, we don't have to worry about that issue. We're worried about these other issues." So that change has cost the industry a ton of money.
Are there other unique aspects about Oklahoma's geology that make it earthquake-prone?
The formation it goes in is probably one of the most permeable injection formations in the world, meaning it could take the most water the fastest, of any of these formations that are used for injection. The trick is we don't have a lot of data on what's going on down there. And so we don't have monitoring.
It's several million dollars to put in monitoring locations here. So we don't have significant monitoring down at depth, except for in the injection locations. When we started getting seismicity here, the problem is that there's no particular formation between the Arbuckle and the basement, isolating it, there’s no shale or something that's going to block water from getting into the basement.
How many wells are you talking about in Oklahoma that do this?
In the seismically active zone, there's roughly 500.
Seems like a manageable number.
But I think it's about 92 different companies, not something where the economics is driven by one company making adjustments in 500 wells.
Is any re-engineering of wells happening?
We've spent, it's estimated. around $30 million so far re-engineering these wells to be seismically safe. In Oklahoma we're retroactively designing these things and asking companies to please take these steps.
And have we gotten better at pinning certain seismic events to certain wells?
No. It's gonna get worse over time, actually. Because as the amount of time goes on, the ability for one well to interact with another well goes up. But the distance is a really interesting scientific and legal issue. Because if you have seismicity occur, people want to point back to a well and say, "Those guys are the ones that did it."
When talking about the earthquakes, you use an analogy that must hit home really well. You say, "The Dust Bowl didn't have to happen, 'cause the science was there.” What do you mean by that?
As a kid, I heard about the Dust Bowl. And working in the environment, you hear about the Dust Bowl. My perception was always, "Well, those people just didn't know. They were too ignorant of the science, of how to deal with crop rotation and which properties deal with in drought and what things you should do."
So when the politicians are saying we want the science to be sure, I didn't want to have a major quake, and then have people say, "Well, if only the scientists said something, we would have avoided this. We were all wonderful people waiting for the scientists to come out of the lab and give us an answer."
But on a scientific basis, we could tell them, "You probably want to do something about this. You want to alter your injections rates and locations, because this is a problem. And if you would like absolute surety, you could go drill some locations and get some wells installed to monitor things. But in the absence of that, we have enough data to tell you that you need to fix this problem, because it's only going to get worse."
america.aljazeera.com
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