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Arkansas's natural gas wells shoot pressurized water deep into the earth to extract natural gas.  (Source: CNN)

The recent rash of earthquakes has been centered around the wells (red boxes added for emphasis of well positions), along the fault line (orange highlight added for emphasis).  (Source: Arkansas Geological Survey)

The quakes rocked the rural region north of Little Rock, but have slowed in frequency since the wells were shut off in March.  (Source: CNN)
A record number of earthquakes of increasing strength struck the region after wells were brought online

No, it wasn't Nikolai Tesla returning from the grave to stir up a little more mischief with his reciprocating machine.  But if reports from Arkansas state scientists are to be believed, the recent rash of earthquakes that struck the state are manmade in nature.

Companies are often quick to suggest that America is simply being negligent complaining about oil and natural gas, when it sitting above vast buried reserves.  But according to some, recent incidents in Arkansas illustrated that there's sometimes more to the picture.  Drilling, they say, can be dangerous and costly.

Arkansas has periodically been hit by small quakes throughout its long colonized history.  

However, in the rural area north of the state's capital, Little Rock, something strange was afoot.  Starting last September the quakes began to get stronger and more frequent.  Suddenly quakes would occur on a daily basis.

At a town hall meeting one citizen bemoans, "If the earthquakes continue to get stronger and stronger and stronger (sic), it's going be people's homes ruined, and possibly people's lives."

State geologists with the Arkansas Geological Survey became alarmed.  Since last September, 1,200 small quakes had struck the region, including a magnitude 4.7 quake, the likes of which had not been seen in 35 years.  Investigating, the geologists found a surprising connection -- natural gas injection wells had been brought online at the same time as the quakes began.

The natural gas facilities use injection wells.  Injection wells are the most common way to extract deep oil or gas deposits.  They shoot pressurized water or steam deep into the Earth's crust, washing up the lucrative hydrocarbons.

But in the case of the Arkansas wells, state geologists say the wells were near a fault line and that the disruption of deep sediments triggered local instabilities, which they believe caused the earthquakes.  Nearly all of the quakes occurred between the major wells, geographically.

States Scott Ausbrooks in a CNN interview [video], "These wells went online and the earthquakes definitely went up in number and size of earthquakes.  If there's not some sort causal relations it is going to be an extraordinary coincidence."

The natural gas companies disputed the theory, saying that not enough evidence existed to show a clear correlation.  One company accused state officials of being in "a rush to find a villain."

Nonetheless, they shut off the wells in March.  And according to state officials, the quakes have grown less frequent.

Natural Gas extraction operators and pro-gas regulators still aren't convinced, though.  States Shane Khoury, AR Oil and Gas Commission, "The better question is whether [the quakes] are being induced or enhanced in any way by the injection operations in or both of these wells."

Of course, this is the kind of case where science may never be able to absolutely "prove" what happened beyond a doubt.  Nonetheless, a clear link between the injections and disruption of the local fault appears to have played out.  

The good news is that not all oil and natural gas sediments across the U.S. fall near fault lines.  The bad news is that some do.

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Dubious conclusion
By theapparition on 6/20/2011 9:27:40 AM , Rating: 1
Correlation does not imply causation.

But at the same time, I have to say 1000 small quakes are significantly better than letting the stresses build up in the fault line causing a major slippage that will really cause some damage and loss of life.

They should look into this method to improve slipage in other faults, such as the San Andreas. On second thought, forget it, let California break off.

RE: Dubious conclusion
By AnnihilatorX on 6/20/2011 9:52:34 AM , Rating: 2
Yes correlation does not always imply causation, but it does sometimes.

Investigating, the geologists found a surprising connection -- natural gas injection wells had been brought online at the same time as the quakes began.

You can't say in this case for example the quake brought online the natural gas injection wells! You can argue they may have no links and the correlation is coincidence. But given you are tampering with the geology and there is a direct physical link, it's pretty absurd to rule it out.

Of course you can't rule out a 3rd connecting factor, but in the case here, one variable (the activity of injection wells) is controlled by man, and it's impossible to imply causation the other way round.

RE: Dubious conclusion
By weskurtz0081 on 6/20/2011 11:16:17 AM , Rating: 3
Hmmm, this is interesting, but the plates that cause serious earth quakes, aren't they MUCH deeper than we are drilling?

RE: Dubious conclusion
By Exirtis on 6/20/2011 11:34:28 AM , Rating: 3
Not necessarily. Quakes come from a variety of depths and a variety of fault types (strike, slip, etc.).

It is an interesting question, however, as to whether a short-term increase in quake frequency might lead to a long-term decrease in quake severity—by a reduction of stress in a fault.

Of course, it's also possible that a reduction of stress in one area could cause an increase in areas adjacent; transferring movement-pressure to a more focused point, so that a more concentrated, sudden, and catastrophic slippage may eventually occur 'downstream.'

RE: Dubious conclusion
By StanO360 on 6/20/2011 12:04:39 PM , Rating: 2
These wells are deep, that's why the whole water "contamination" thing is a hoax.

RE: Dubious conclusion
By kattanna on 6/20/2011 1:09:35 PM , Rating: 3
so you honestly think that when you inject millions of gallons of water and various chemicals to crack open rock and make it more porous for the gas/oil to be extracted..only the gas/oil will flow to the surface?

RE: Dubious conclusion
By Reclaimer77 on 6/20/11, Rating: 0
RE: Dubious conclusion
By croc on 6/20/2011 10:24:31 PM , Rating: 2
Reclaimer, there are many faults that have no apparent connection to any tectonic plate. The recently discovered (and deadly) fault in Christchurch NZ is such a fault, as is the New Madrid fault located in your own midwest.

RE: Dubious conclusion
By sonoran on 6/20/2011 10:04:30 AM , Rating: 4
I couldn't help but think the same thing as I was reading this. Having a lot of tiny quakes that cause little or no damage would be preferable to a megaquake that does massive destruction and kills tens of thousands (or worse).

Of course there are also the inevitable unintended consequences - which no on yet knows about or understands. Allowing one fault to move more freely could cause pressure to build up on others faster?

RE: Dubious conclusion
By therealnickdanger on 6/20/2011 10:58:40 AM , Rating: 3
But what if the thousands of small quakes work to weaken the surround earth and loosen a potentially larger one that otherwise would never happen? You may wonder if this prevents the Big One™, BUT what if it causes the Big One™? I don't think we have the understanding to make that conclusion yet. Far too many variables.

What seems to be known at this point is that these quakes all started after activating the system. The only way to prove it is to test it more.

RE: Dubious conclusion
By Shadowmaster625 on 6/20/2011 11:12:50 AM , Rating: 2
hush hush... let them live in their happy little delusion where they think they know that much about geology. Is there any actual proof that causing small earthquakes mitigates the probability of a large one?

RE: Dubious conclusion
By Manch on 6/20/2011 2:05:07 PM , Rating: 2
Exactly. One of the major issues with the areas they are drilling in Arkansas is the majority of the ground above is already loose sediment. If there is a major earthquake similar to the 1812 New Madrid the worry is that the ground will "liquify" and everything will "sink" If there is a connection between the drilling/mining and the earthqukaes is needs to be proved/disproved before they resume.

RE: Dubious conclusion
By Paj on 6/20/2011 11:46:16 AM , Rating: 2
Considering how undeveloped seismology is, its probably best to err on the side of caution don't you think?

RE: Dubious conclusion
By toyotabedzrock on 6/20/2011 12:10:24 PM , Rating: 2
ou cannot prevent earthquakes by creating smaller ones.

Do many small earthquakes prevent larger earthquakes?:

No. Observed numbers of small earthquakes are too few to equal the amount of energy released in one large earthquake. (It would take roughly 24 million earthquakes of magnitude 2 to release the same energy as one earthquake of magnitude 7.):

You can prevent large earthquakes by making lots of small ones, or by "lubricating" the fault with water:

RE: Dubious conclusion
By therealnickdanger on 6/20/2011 3:49:51 PM , Rating: 2
You can prevent large earthquakes...

Judging by what you typed before that sentence, and your sources, I assume you meant "cannot". Before anyone gives you a hard time...

RE: Dubious conclusion
By kattanna on 6/20/2011 1:07:24 PM , Rating: 2
while it is entirely possible that the wells have nothing to do with the quakes initially

Nonetheless, they shut off the wells in March. And according to state officials, the quakes have grown less frequent.

but after shutting them off and having the quakes subside, makes for a strong case of the wells being at least part of the issue.

if they really wanted to further their claim, they should turn the wells back on/off multiple times and see if the quakes continue to respond accordingly.

though, in all honesty, it doesnt take a great leap of understanding to see how injecting millions of gallons of water and chemicals into a known fault zone could lead to more quakes, just like adding a lubricant between 2 panels allows them to more easily slide past one another.

RE: Dubious conclusion
By FaaR on 6/21/2011 5:09:49 AM , Rating: 2
I'm not so sure water and chemicals really lubricates rock all that well, I'd be more concerned with the deformation of the surrounding local area introduced by pumping liquid down into the ground. Water doesn't compress (very much anyway) even at extreme pressures, so to make room for itself it would have to push outward on surrounding materials.

I wouldn't be surprised if that had a greater effect on shifting around stress in a faultline.

Hydrofracing basics.
By OSD237 on 6/20/2011 11:11:59 AM , Rating: 3
there are a few small errors in the article (sorry for being pedantic).

A "normal" oil reservoir has a cap rock which is impermeable, and then the reservoir rock which is porous and permeable (sandstone or some form of carbonate usually), with a source rock somewhere nearby.

In shale reservoirs (which used to be considered cap rocks, and are cap rocks in places like the North Sea), the porosity is usually low (can easily be less than 5%), with almost non existant permeability in the nano darcie range (in comparison some carbonates have permeabilities in the 100 darcie range). The shale also acts as the source, cap and reservoir rock all at once. The shale has kerogen in which has broken down slightly to give off gas (methane usually). Obviously as shale is "impermeable" you will never naturally get enough of the hydrocarbons off to make the well economical. By hydrofracing (hydraulic fracturing) you pump large volumes of water down a well (in the case of shale horizontal wells) , to fracture the rocks, and then use propants (ceramic beads etc) to keep open the newely created fractures. This greatly increases the surface area of the well and allows more gas out making it economical.

It shouldn't be much of a suprise that "micro" earthquakes are common - you are breaking rock apart. The surprise is the 4.7(? don't have the article infront of me but its listed in that). By adding large amounts of water to a fault system you might allow the lubrication of fault planes (it has happened in the North Sea and in a Swiss Geothermal Experiment), but I would have thought that once the initial hydrofrac stage had occured the frequency would decrease as the stress was transfered.

Depending on the seismic profile of each of the earthquakes you should be able to see if they have a similar source and work out the relative motion which would give some idea as to pressure building up or being released.

RE: Hydrofracing basics.
By StanO360 on 6/20/2011 12:10:35 PM , Rating: 3
I'm very skeptical. Because this should be addressed statistically not anectodally. They have the past quake information probably for 40 years. So the simple question is do these deviate from the norm by a statistically significant amount?

If they do, by how much? Then the question is, is it harmful?

RE: Hydrofracing basics.
By FaaR on 6/21/2011 5:22:15 AM , Rating: 3
Determining how harmful it might be could be difficult considering human attention spans on a geological scale. Economic interests in particular tends to work towards if nothing bad has happened in say, six months or a year or possibly two, then the rationale is going to be nothing bad will, or even can happen, ever. Because companies want to make money, and machinery sitting still generate no revenue and worrysome talk over quakes scare off investors.

With a human working life being about 50 years at most and seismic stress building up over centuries or more, it might take generations for us to really know if hydrofracturing can contribute/cause big quakes - by which time nobody will either care anymore, or even if we do, it will be too late to do anything about it. :-P

RE: Hydrofracing basics.
By Captain Orgazmo on 6/20/2011 4:24:37 PM , Rating: 2
Hmm, sorry to be pedantic, but shale porosity is usually pretty high, up to 40%, just the permeability is very low. Also, the North Sea has many different shale formations, ranging from 3% to 24% porosity.

You are correct about everything else. I have seen first hand on a shale gas operation how fracking can cause micro-quakes and even larger earthquakes from fault slippage (enough to feel the ground shake a bit, but not enough to cause real damage). The slippage was enough in one case to shear a wellbore and drop a few hundred thousand dollars worth of downhole tools to the bottom. Also it caused ESDs on the gas plant daily due to turbine vibration sensors being tripped.

I have a big problem with this article however. First of all, I have never heard of "Natural Gas Injection Mining". The term is probably a government classification name for granting permits. From the poorly written article it sounds more like waterflood (a method of secondary recovery), rather than hydraulic fracturing. If it is indeed waterflooding that they are claiming is causing these quakes, I call BS, as the pressures involved in the water injection are not high enough.

I would hope that there is a better researched followup to this article, as there is already too much layman propagated misinformation floating around about this important issue. A nation's energy supply is vital, and it is being made into a political football by American politicians of all stripes for varying reasons, many of which are not valid. For example, the failure to allow the building of the Keystone XL pipeline to transport crude oil from Alberta to the US would be a major mistake considering the US's largest external supplier of oil and gas is Canada. On the other hand, shale gas development needs to be carefully monitored, because it involves new methods and technologies, and has the potential for causing many problems.

RE: Hydrofracing basics.
By TDSCOTT on 6/20/2011 11:52:16 PM , Rating: 2
Good post. The wells they are talking about are Disposal wells.

New Madrid fault
By Natch on 6/20/2011 10:03:51 AM , Rating: 2
Just thinking how, wouldn't it be a trip if the New Madrid fault ( ) was being kept from having it's next major quake by natural gas pressure, and drilling for that gas caused a quake?

It's said that the New Madrid fault, while not as extensive as the more famous San Andreas fault, could possibly put out a quake equal in magnitude to anything the west coast fault has, possibly matching (or even exceeding) the strength of the earthquake that hit Japan recently.

If you ever wanted to see old Memphis, and haven't already, you might try getting there soon.....because it's expected those old brick buildings there will be so many piles of rubble, if a major quake hits the New Madrid fault.

RE: New Madrid fault
By Shadowmaster625 on 6/20/2011 11:15:50 AM , Rating: 2
You obviously cannot comprehend the amount of energy released during a major earthquake. Nothing we do with gas wells can come close to even a 1/1000th of that energy.

RE: New Madrid fault
By Natch on 6/20/2011 1:29:52 PM , Rating: 2
And I believe that you miscomprehended my point. Which was, what if the gas pressure was somehow helping to prevent the next big quake, and by drilling for gas, and releasing that pressure from where the gas is located, it then made it easier for the quake to happen?

Pure conjecture, but an interesting possibility (at least, in my mind).

So far as the force released during an earthquake, having been through more than a few major quakes in my lifetime (of magnitudes greater than 6), I'd say I have some small amount of knowledge as to what they felt like. May not be as good as sheer numbers, but it's more than most people have.

RE: New Madrid fault
By espaghetti on 6/20/2011 12:45:27 PM , Rating: 2
Sorry, the last time I was over in Memphis, I was trying not to get shot or mugged.
Not really worried about old buildings.
I live on the New Madrid fault. I'll suffer a few small shakes for lowering my crazy natural gas bill.
Way too much fear mongering over where we get our energy from.
It gets exhausting.

Not to nitpick, but...
By RivuxGamma on 6/20/2011 11:22:15 AM , Rating: 5
Nikolai Tesla? Nikolai?

Come on. For such an influential figure that gets little recognition we could at least get his name right.

RE: Not to nitpick, but...
By Gondor on 6/21/2011 2:49:29 AM , Rating: 2
Nikola - the trailing 'i' is silent ;)

By Flunk on 6/20/2011 11:28:51 AM , Rating: 2
Evil energy companies drilling for oil causing earthquakes? Why does that sound like the plot of an episode of the old Captain Planet TV show?

Silliness aside, they need to look into this to confirm that it's really happening. Correlation is not solid proof. If this is true it means will have to re-evaluate injection mining techniques.

Don't punch too hard
By TDSCOTT on 6/20/2011 11:46:11 PM , Rating: 2
I could be wrong but I think there is some misinformation here. First of all the wells that I know of that were shut in because of the earthquakes were “Disposal” wells. These wells were not producing but rather a well to dispose of water produced during the gathering of natural gas. Water from producing wells contains high concentrations of salts. This is naturally accruing at these depths and must be disposed of. The logical answer is to put it back in the ground. This has nothing to do extracting gas. It does not have anything to do with fracturing operations. It is just returning the saltwater back to the ground. I will agree the facts show it may have increase the earthquakes and the wells have been shut down but don’t amalgamate this into the gas industry as a whole. The companies that drilled these wells have lost millions on these wells. Arkansas is one of just a few states that have a budget that is not operating in a deficit. Keep punching this industry and we will join that list of states in the red. Can anyone post just how many Arkansans are employed by the gas industry?

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