Oklahoma’s earthquake epidemic linked to fracking wastewater disposal
A Consol Energy Horizontal Gas Drilling Rig explores the Marcellus Shale outside the town of Waynesburg, PA on April 13, 2012. MLADEN ANTONOV/AFP/Getty Images
Oklahoma has unexpectedly become the earthquake capital of the United States — with some 240 small earthquakes magnitude 3.0 or more already this year. That’s about twice as many as California has gotten.
A new study links the earthquakes to the wastewater disposal wells
And in a new study in Science, researchers say they’ve pinpointed the culprit: the wastewater disposal wells used by the fracking industry.
Back in 2008, energy companies began ramping up the use of fracking for oil and gas in Oklahoma. The fracking process typically involves injecting water, chemicals, and sand underground at high pressures to crack open shale rock and unlock the oil and gas inside.
Fracking itself doesn’t seem to be causing many earthquakes at all. However, after the well is fracked, all that wastewater needs to be pumped back out and disposed of somewhere. Since it’s often laced with chemicals and difficult to treat, companies will often pump the wastewater back underground into separate disposal wells.
Wastewater injection comes with a catch, however: The process both pushes the crust in the region downward and increases pressure in cracks along the faults. That makes the faults more prone to slippages and earthquakes.
And as it happens, Oklahoma has seen a sharp rise in earthquakes since 2009. (Before then, magnitude 3.0 earthquakes were extremely rare):
Earthquakes in Oklahoma between 1976-2014. Earthquakes are magnitude > 1 from the NEIC catalog. Keranen et al 2014
The latest Science study, led by Katie Keranen of Cornell, says this is no accident. By analyzing seismic data in Oklahoma along with the location of some 10,000 disposal wells along the state, the researchers concluded that there’s a likely link between the two.
Just four wells were likely responsible for one-fifth of seismic activity
More specifically, the researchers concluded that 89 wells were likely responsible for most of the seismic activity. And just four wells located southeast of Oklahoma City were likely responsible for about one-fifth of seismic activity in the state between 2008 and 2013.
It’s worth noting that so far these earthquakes have been too small to do serious damage or endanger lives. Still, they seem to have stirred up concern among some Oklahoma residents, and regulators are now considering whether additional rules may be necessary. This new research could help more accurately pinpoint the links here.
Previous studies on earthquakes and wastewater wells
The Science study is hardly the first to suggest a link between wastewater injection and earthquakes. Kansas, Texas, and Ohio are also all exploring possible connections. Over the past year, the US Geological Service had also suggested a link between wastewater wells and earthquakes.
Meanwhile, a separate study is currently ongoing in Colorado as to whether an injection well was causing seismic activity near Greeley. One June 25, state regulators ordered a halt to wastewater injection in the area after a 2.6 magnitude quake (which had followed a 3.4 magnitude quake in May).
How does fracking work, exactly?
Using hydraulic fracturing and horizontal drilling to extract oil or gas from shale rock involves a number of steps. Let’s walk through a basic fracking operation for natural gas in, say, the Marcellus Shale in Pennsylvania:
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1) First, a “wellbore,” or hole, needs to be drilled all the way down to the layer of gas-rich shale. This shale layer can sit more than 5,000 feet underground and drilling can take as long as a month. The well is lined with a steel casing to prevent the contamination of nearby groundwater.
2) Once the drill reaches down to the shale layer, it slowly turns and begins drilling horizontally, for a mile or more along the rock.
3) A “perforating gun” loaded with explosive charges is lowered to the bottom of the well and punctures tiny holes in the horizontal section of the casing that’s deep down in the shale layer.
4) Now comes the actual fracking, or “completion” stage: A mixture of water, sand, and chemicals is pumped into the well at extremely high pressures and goes through the tiny holes in the casing. The fluids crack open the shale rock. The sand holds those cracks open. And the chemicals help the natural gas seep out.
5) The “flowback” stage: The water and chemicals flow back out of the well and are taken for disposal or treatment.
6) Finally, natural gas begins flowing from the shale and up out of the well, where it’s eventually shipped to consumers via pipeline. A typical well can produce gas for 20 to 40 years, pumping out thousands of cubic feet of gas each day.
That’s a very rough overview of the fracking process. There are plenty of variations, depending on the geology of the region or the technologies used. (Often other particles besides sand are used, for instance. And here’s a partial listing of some of the different techniques used in North Dakota, for example.)