Hydraulic fracturing, also called hydrofracture or just fracking, is a commonly used method to increase the yield of fluid raw materials, usually petroleum or natural gas, from formations that are not “easy” extraction targets. Easy targets are ones that the fluids dispersed in sands or very porous rock formation.
Let us dispel a common myth right now: oil and gas is almost NEVER found as big pools of those materials in large holes in the rock. Almost without exception, and perhaps quite without exception, these materials are dispersed in some more or less porous rock or sand. When you see pictures of underground reservoirs of gas or oil, you are really looking at the fluid as it is dispersed in the native matrix.
Sand and very “rotten” sandstone are easy matrices from which to extract the fluids. Shale and hard sandstone are much more difficult matrices, and hydraulic fracturing is used to increase yields from such formations.
I begin this with a new tradition. The arts are important, and I plan to begin and end my posts with some. Since I do not have the technology to read poetry here, let us enjoy a very obscure cut by The Who, Mary-Anne with the Shaky Hands, the Hammond organ version. Please enjoy it with me. If anyone knows how to allow me to read poetry here, please comment or write to let me gain that skill. Note that many of the stills here are of the extremely attractive Diana Rigg, Mrs. Peel from The Avengers. Girls from the 1960s, Rigg or others, are extremely attractive. I was born either too early or too late. Perhaps it is they way they look, or the color of their hair, or if their eyes were clear and bright. Well, that just provided a segue for next week’s Popular Culture, an expose about one of the best, and most short lived British bands, The Zombies. Hardcore Zombie fans will recognize the joke.
A couple of days ago in central Arkansas, a 4.7 earthquake was experienced. That region of the state is pretty “quiet” seismically (but not completely inactive), in a different geological zone from the seismically unstable New Madrid Fault Zone, which is in extreme northeastern Arkansas and southeastern Missouri. The New Madrid Zone has been responsible for some of the most powerful earthquakes in the continental United States, but it is associated with a mantle hot spot. In the early 1800s, earthquakes there were frequent and extremely strong, upwards of 8.2 or more.
Here is a link to a TeeVee news piece about it. Note that the newsreader near the end of the piece is mistaken about the size of the 1811 temblor. Unfortunately, the embed code was not available.
Now, a 4.7 earthquake may not sound like a bid deal, but in central Arkansas there are essentially no building codes for earthquake resistance. You reading this in California may sort of chuckle about a 4.7, but one in Arkansas can be devastating. Fortunately, this one had its epicenter in a rather sparsely inhabited region.
Such a large temblor in that region of Arkansas got me to thinking, as as The Geek is wont to do, rooting around for more information. It turns out that one of the prime suspects for this earthquake is hydraulic fracturing. Now, this is certainly not established yet, since the event was only a couple of days ago, either scientifically nor legally, but there was enough concern for the Arkansas Oil and Gas Commission to suspend the disposal of spent hydraulic fracturing liquids by deep well injection until more information is available.
Let us look into the hydraulic fracturing process a bit more closely. First, it is informative to examine fluid (let us confine our discussion to natural gas, but the concept is quite general) extraction from underground reservoirs. In a nutshell, a potential field is located, and one or more exploratory wells are drilled. If those wells show that the location is likely to produce economically viable amounts of gas, then production wells are drilled. In an “easy” field, the matrix containing the gas is very porous, usually loose sand or rotten sandstone or shale, as indicated in the introduction.
In that case, essentially all that has to be done is to drill a well, sink a casing as the drilling proceeds, and allow the natural pressure of the formation to push out the gas. The casing is necessary to prevent the sand or rotten rock from closing off the drill bore. After a while, the natural pressure equilibrates with the surface pressure, so pumps are often needed later in a rich well’s life, but the gas is still easy to pull to the surface.
In a “hard” well, the rocky matrix is much less permeable to fluid flow than sand or rotten rock. Now, hard matrices may contain as much or even more gas than easy matrices, but because of the low permeability it does not “want” to release it at an appreciable rate. To change the permeability, fluids are injected to break up the rock, to fracture it, so that it becomes more permeable, thus allowing the fluid to drain from it faster.
Before we continue, let us think for just a minute. ANY underground formation, when deprived of the fluid that is part of its support, has less structural integrity than it has whilst the fluid was still there. That is just physics. On the other hand, a relatively stable formation, when having material ADDED to it, may become unstable if the offsetting forces are overcome with the added load. It works both ways. Now, rock is pretty hard to move, but porous structures are a little different. We shall return to this later.
In hydraulic fracturing, liquids (usually) are injected under very high head pressures with powerful pumps (below the well casing) to cause the rock to separate along natural lines of weakness. The result is that the effective surface area of the gas bearing rock is increased so that the flow of gas into the casing is increased, thus increasing the yield. Economically, that is a good thing for the gas companies.
Normally the fluid used is mostly water, with a few additives. The actual additives are proprietary in most cases, and often include disinfectants like bleach or caustic to decrease the populations of microbes, which often tend to form biofilms and clog up the works. Sometimes other agents are added to the fluid, but my research for this piece indicates that they vary widely, and often depend on the particular company and even the engineer with a given company. The end result is that some hydraulic fracturing fluids are quite innocuous, and some are quite toxic. There is a very wide range.
Normally, after the fractures are induced, a slurry of what I call wedging agents (I believe that the industry term is proppants)are pumped into the fractures. These agents are solids, and are intended to replace the high pressure water in the fractures. If one thinks about it for a couple of seconds, the high pressure required to fracture the rock also keeps the gas from coming out of it. The wedging agents, often spherical sand (it does not pack down like irregular sand does) or other proprietary materials hold the cracks open after the hydrostatic pressure from the high pressure pumps is released. Now the gas has an easy pathway, through the wedging agents to the well casing.
So far, not so bad. Actually, the wedging agents sort of help to prevent collapse of the formation since they occupy space. My research has turned up few significant seismic events from the procedures as they go this far, but a few cases do indicate that some minor events, less than 3.0 MIGHT have to do with them. The science is actually very spotty and poor right now.
It seems what happened in Arkansas was that the nature of the fluids used for hydraulic fracture came under the definition of a toxic waste, and could not just be discharged to the land or to waterways. The companies were granted a permit for deep well injection, purportedly a way to isolate those materials in perpetuity by injecting them very much deeper into much more dense, but yet somewhat permeable strata. This is where the hypothesis that earthquakes were caused by hydraulic fracturing comes into place.
This is just an hypothesis, and I am not sure that it is correct, but certainly should be considered. It is not an hypothesis that I came up with on my own.
The idea is that the spent fracking fluids are injected very deep, and into perhaps stable, for the moment, formations. Now, you can not inject water into solid rock, so there must be some space for it. Good luck with the syringe and piece of granite! LOL! As a matter of fact, the injection wells are pumping the spent fluids, and lots of them, into a region near known fault zones. I mentioned earlier that this region is fairly stable, but there have been small earthquakes in the vicinity off and on for decades. Going back to the piece of granite analogy, either some faulting is necessary or some permeable region is required (or both) to give the fluids a place to go.
The thought is that as the fluid migrates into the fault areas, exerting pressure in already stressed regions. This pressure reduces the friction betwixt the two parts of the existing fault, making it easier for movement to occur. It remains to be proven scientifically that this is what is occurring in Arkansas, but there is some historical precedent. A number of years ago a similar situation occurred in Texas, and after deep well injection was halted, the earthquakes subsided. Now, coincidence does not require causality, but this is a subject that needs more study, and fast.
Now, please realize that these are only loose connexions. The science is not very good, largely because lack of verifiable data. But hydraulic fracturing is not anything new. It has been used for over a century to separate the granite deposits from bedrock in North Carolina, but that is hardly a deep well application. However, I suspect that when those slabs of granite separate a seismometer would record the event at 4.7.
It seems that our old friend, The Halliburton Corporation, was responsible for the initial large scale use of this technique. Go figure. However, they were far from the first to use it. A USGS bulletin describes it for the granite recovery in 1910! However, its use for gas and oil production enhancement seems to go back to around 1947 or so, and Halliburton commercialized it in a large way in 1949. Thus, this is nothing new.
Oil and gas companies hold more seismic data than all government stores combined. I believe that it would be very instructive if they were required to release ALL of their raw data for a real scientific examination. I strongly suspect that we might get enough real data to examine the question in a scholarly manner, but I also do not expect them to do that because of “proprietary information”. You know as well as I do that they have extreme interest in the seismic events, and how that they relate to enhanced product production.
I am not an expert in this field, but I have neither made any unequivocal comments about it, either. I have reported the basic processes and also some of the unanswered questions. Do I think that the injection of spent fluids caused the earthquake? I think that it might be related to those events, but I am far from sure. More research needs to be conducted, and much more close monitoring needs to be done.
I call for persons with much more expertise than I have to chime in and comment. Please correct me where I may have been incorrect, and please illuminate in your comments better information. If you have good scientific evidence and conclusions, please add them. If you have only your speculations, please label them as such. This is am important topic as natural gas becomes a more important domestic fuel. Central Arkansas is a rich bed for it right now, and those folks do not need any more earthquakes.
Well, you have done it even again! You have wasted many einsteins of perfectly good photons from around 400 nm to 800 nm (actually, more complicated than that, and the first one to tell me why wins The Geek recognition tonight) by reading this oily post. And even though Mike Huckabee (my former Governor) now says that President Obama grew up in his clothes closet in Arkansas when he reads me say it, I ALWAYS learn much more than I could possibly ever hope to teach in writing this series. Thus, please keep those comments, questions, corrections, and other thoughts coming. This week, please keep better expertise than mine coming.
I shall stay around as long as comments justify tonight for Comment Time, and shall return tomorrow around 9:00 PM Eastern for Review Time. Remember, the rules are that I can not look anything up for Comment Time, but am allowed to do so before Review Time.
In keeping with the new tradition, here is Sally Simpson from the seminal work by The Who, Tommy.
I do now know what has gotten into me this evening, with the affection for women from The Who. I shall bring other things in future installments, but I do think that some art to liven up Pique the Geek is in order. I would to have some Kipling here, in my own voice, but need instruction as to how to digitize sound and then the You Tube thing.
Warmest regards,
Doc
Crossposted at Antemedius.com, Dailykos.com, Docudharma.com, and Fireflydreaming.com.
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