Evidence linking carbon dioxide (CO2) injection to earthquakes may be bad news for carbon capture and storage.
The extraction of both natural gas and crude oil has risen sharply in the United States since 2005 and 2010, respectively. And, interestingly enough, the typically quiet midcontinental United States has also experienced an increase in earthquake activity. How big an increase? A pretty substantial one; in a paper presented at the Seismological Society of America’s annual meeting in April 2012 W.L. Ellsworth of the U.S. Geological Survey and co-authors called it "remarkable.”
Between 1970 and 2008 the area that spans westward from Ohio to Colorado and southward from North Dakota to Texas (see map) saw between 20 and 30 magnitude-3 or larger quakes per year. However, between 2009 and 2011, when the practice of horizontal drilling and hydraulic fracturing (fracking) ballooned, the number of such large quakes skyrocketed: to 50 in 2009, 87 in 2010 and 134 in 2011. As Ellsworth et al. said -- it's remarkable.
Clearly something's going on. Could it be related to the fossil fuel industry? There seems to be an overall correlation between the uptick in both fracking and quaking, but a correlation does not a cause-and-effect relationship make. So scientists have, shall we say, drilled down into the data to try to figure out what's happening.
Fossil Fuel Extraction
There is some, but very limited, evidence tying the extraction (or mining) of fossil fuels to earthquakes. For example, a 2011 report [pdf] by Austin Holland of the Oklahoma Geological Survey cites evidence suggesting that fracking caused some 43 magnitude-1 to magnitude-2.8 earthquakes in southern Oklahoma.
There is far more -- and more compelling -- evidence linking seismic activity to the high-pressure injection of wastewater from oil and gas extraction into deep wells (see insert). Some examples:
Developing & Producing Oil and Gas: A Water-Intensive Affair
The development and production of oil and gas -- particularly unconventional shale gas and tight oil -- are water-intensive activities. Developing just one unconventional shale gas well typically uses 3 to 5 million gallons of water [pdf] although the upper range can be much higher (on the order of 13 million gallons).
During these activities, additional wastewater, known as flowback and produced waters, flows to the surface and requires disposal or recycling. Once a well is in production it will be reworked (refracked) on a regular basis using more millions of gallons of water.
Unconventional oil wells use similar amounts of water with a typical well in the Bakken shale field using 1.5 to 4 million gallons per frack.
As you might imagine, the wastewater from these activities can be highly contaminated; so much so that you can't just pour it down the local municipal sewer. So what do you do with all that contaminated water? One popular solution has been to inject it deep below the surface.
1) In Youngstown, Ohio, seismic activity between 2011 and 2012 -- including one magnitude-4 quake -- was linked to the high-pressure disposal of fracking wastewater in a well near an undiscovered fault line.
2) A 5.7-magnitude quake in Oklahoma in 2011 is believed to be linked to the disposal of fluids used in oil production.* (See also here.) And by the way, a quake of that magnitude, the largest to be linked to fluid disposal, is no joke. This one was felt in 17 states and, as reported on Columbia University’s Lamont-Doherty Earth Observatory website, "destroyed 14 homes, buckled a federal highway and left two people injured."
3) Seismologist Steve Horton of the University of Memphis reported in a 2012 paper in the journal Seismological Research Letters that "98% of the recent earthquakes [in north-central Arkansas] occurred within 6 [kilometers] km of one of three waste disposal wells after the start of injection at those wells. "
4) Cliff Frohlich of the University of Texas at Austin reported in the Proceedings of the National Academy of Sciences in August 2012 that "[a]ll 24 of the most reliably located epicenters [in the Barnett Shale, Texas, between 2009 and 2011] occurred in eight groups within 3.2 km of one or more injection wells."
A New Way to Shake, Rattle, and Roll Courtesy of Fossil Fuel Industry
Writing in the Proceedings of the National Academy of Sciences last week, Wei Gan, also of the University of Texas at Austin, along with his colleague Frohlich reported on still another way the fossil fuel industry may be triggering seismic activity: via enhanced oil recovery.
This is a technique used to get more oil out of the ground after all the easy-to-get-at oil has been pumped out of a well -- thus the term "enhanced." According to the U.S. Department of Energy, 60 percent of all enhanced oil production is from gas injection, a process wherein gases such as natural gas, nitrogen, or CO2 are used "to push additional oil to a production wellbore." Like wastewater injection, gas injections occur at high pressures.
Gan and Frohlich link a series of magnitude-3 and larger earthquakes to gas injection at the Cogdell oil field in northwest Texas. This appears to be the first documented case linking such enhanced oil recovery to seismic activity.
Trouble for Carbon Sequestration
Now, lots of companies are using enhanced oil recovery in the United States, and the Gan-Frohlich study relates to only one series of earthquakes in one oil field. There is absolutely no evidence to suggest that enhanced oil recovery is a ubiquitous source of seismic activity. Still, the study aptly demonstrates that we don't have a good handle on where quakes will occur and what seismic activity might occur when we inject stuff deep below the ground. And that's got to raise some eyebrows, if not some neck hairs, about the viability of capturing and storing carbon -- a potential way to avoid the emission of CO2 from fossil fuel burning into the atmosphere.
If I may review: burning fossil fuels (especially coal) releases CO2, which contributes to climate change. It is widely believed that sometime in this century we're going to have to stop those emissions to avoid dangerous climate change. One way to accomplish this is to completely kick the fossil fuel habit and embrace renewables and there are those who claim we can do it. (See here and here.)
But there are others who are a lot less sanguine -- renewables are just not ready to take the place of fossil fuels any time soon, they argue.
So what's to be done about the climate problem if the renewable-energy skeptics are right?
Carbon capture and storage could hold part of the solution to that quandary. Burn the fossil fuels, but snag and store the carbon dioxide to keep it from getting into the atmosphere. It's a great concept, but there are practical issues. One is finding a technology to capture the carbon dioxide efficiently and cheaply. Another is where to store the CO2. The most popular answer to the storage challenge is to inject the CO2 deep under the ground. Essentially, find old wells and other deep geologic features and inject the captured CO2 into them. Kind of like what is done when gas is used to enhance oil production.
And there's where Gan and Frohlich's work highlights a potential pitfall in carbon capture and storage. Who's going to allow the injection of CO2 into the ground near their home if an earthquake could be in the offing?
I mean let's face it -- no one likes it when the earth starts moving under their feet. It can even cause their hearts to start to trembling.
* The Oklahoma Geologic Survey is on record with findings that natural causes for the magnitude 5.7 quake cannot be ruled out.