Fracking and Earthquakes: The Tightest Link Yet

Stanford scientists have found the best evidence so far that injections of wastewater from hydraulic fracturing (fracking) oil and gas wells definitely cause earthquakes.  The next question is, how will the Texas Railroad Commission and the oil and gas industry respond?  But first, the scientists' study.

As readers of this blog may know, fracking involves the injection of special mixtures of water and proprietary stuff at extremely high pressure into specially drilled wells that penetrate oil- and gas-bearing formations which normally would not produce enough to be worth drilling into.  The producing wells are not the problem.  The problem is that a byproduct of the process is a huge amount of wastewater contaminated with salt, chemicals, and sometimes even radioactive stuff, and these days you don't just dump it out on the ground or into a nearby stream.  The drillers gather it up with tank trucks and ship it to disposal wells, where it is squirted several kilometers deep into rock formations under tremendous pressure. 

It's these disposal wells that seem to be associated with spates of earthquakes in north Texas and Oklahoma, which up to 2000 or so were some of the most earthquake-free areas in the U. S.  Fortunately, most of the earthquakes have been small—around 3 on the "moment magnitude" scale, which replaced the old Richter scale in the 1970s.  But a 4.8-magnitude quake on May 17, 2012 in the East Texas town of Timpson (about halfway between Lufkin and Longview) knocked down a brick wall, and turned out to be the largest such quake ever recorded in that area in recent times. 

Stanford geologist William Ellsworth, working with an international team of geophysicists, remote sensing experts, and others, decided to build a model of the subsurface rocks to see if they could reproduce the conditions that may have led to the earthquake.  Fortunately, that part of Texas is well-understood geologically, and Ellsworth's team obtained data on how much wastewater was injected into two pairs of wells, each at a different depth.  They also found and enhanced satellite-radar data that can measure movement at the earth's surface as slight as 1 millimeter per year.  They put all this data into a "poroelastic layered Earth model," meaning they accounted for porosity and elasticity—how holey and how flexible the rocks are.  They also knew about existing faults, and ran their model to predict both how much the surface might bulge after getting some 800,000 cubic meters of wastewater injected into it per year for several years.  Then they compared their model's predicted bulge to the measured bulge, which was several centimeters, and got pretty good agreement between their model and the actual satellite data.

That told them that another number their model produced—the increase in pore pressure—was also probably right.  When pore pressure increases by about 10 times atmospheric pressure (1 megapascal or more), this has been shown to cause earthquakes.  The mechanics are complicated, and I'm not a mechanical engineer.  Basically, the reason fault lines under pressure don't slip is that there is a lot of force squeezing the two sides together, and the resulting friction keeps things stationary.  But when you have increased pore pressure on the order of 1 megapascal, that somehow decreases the squeezing force and the thing starts to slip.  And slip it did, causing Timpson's quake and others.

Although most of the bulging occurred around the eastern pair of wells, the western wells were where the earthquake happened.  Ellsworth's team could explain this by citing differences in the porosity and elasticity of the rocks around each set of wells. 

So the scientists have made a model of the rocks under Timpson, injected their rock model with wastewater, and observed both a surface bulge that matches what satellites actually measured, and noted pore-pressure changes of a size that is known to cause earthquakes elsewhere.  And in fact, an earthquake happened.  Looks pretty conclusive to me.  But I'm not a Texas Railroad Commissioner.

What have railroads got to do with oil and gas production?  It's a long story, but basically, the Texas Railroad Commission (TRC), which originally did regulate railroads, backed into the business of granting permits for oil and gas production in the 1930s, and as time went on nobody has had the temerity to change its name.  It apparently did some useful work in the 1930s by putting the brakes on absurd overproduction and keeping oil prices from vanishing.  Nowadays, its regulatory duties are different, and involve environmental concerns as well as the usual support and encouragement of the industry it is charged with regulating. 

In reports describing the Stanford study, attempts by reporters to get a reaction out of the TRC were initially unsuccessful.  The Commission's mission statement has three bullets, saying it serves Texas through (1) "our stewardship of natural resources and the environment" (2)  "our concern for personal and community safety" and (3) "our support of enhanced development and economic vitality for the benefit of Texans."  Judging by the Commission's past reluctance to admit any causal link between fracking and earthquakes, their mission statement's bottom line, about enhancing development and economic vitality, appears to be taking precedence over the other two items, just as a company's bottom line tends to take precedence over other concerns.

Ellsworth and company have confirmed what many other geologists, as well as numbers of ordinary citizens, have been suspecting for a long time.  Most, if not all, of the increased earthquake activity in regions near wastewater injection wells can probably be attributed to those wells. 

By and large, Texans are reasonable people.  Fracking has been an economic blessing to many parts of the state, and it's unlikely that anything like the blanket fracking bans in New York and Maryland could happen here.  But now that there is reasonably good evidence of the connection between wastewater wells and earthquakes, it would only be reasonable for people who have lost property or been injured in such events to ask for compensation from the owners of the wells.  Of course, any time lawyers get involved, reason may fly out the window, but I think we can work these issues out without either continuing to deny that there's any association at all, or saying that fracking is an invention of the Devil and must be abolished from the planet.  Let's hope so, anyway.

Sources:  I referred to a report published online by the Dallas Observer on Sept. 23, 2016 at http://www.dallasobserver.com/news/new-scientific-study-cites-direct-evidence-that-texas-quakes-are-manmade-8736998, one in the Dallas Morning News at http://www.dallasnews.com/news/state/headlines/20160923-texas-quakes-caused-by-injection-wells-scientists-determine.ece, and the paper by M. Shirzaei, W. L. Ellsworth, K. F. Tiampo, P. J. González, and M. Manga, "Surface uplift and time-dependent seismic hazard due to fluid injection in eastern Texas," Science, vol. 353, Issue 6306, pp. 1416-1419, as well as the Texas Railroad Commission website www.rrc.state.tx.us.

Injecting Some Sense Into Fracking Regulation

The July issue of Scientific American carried the best summary of the fracking-earthquake controversy I have seen so far.  "Drilling For Earthquakes" by Anna Kuchment reviews the fracking (hydraulic fracturing), the associated water injection, the earthquakes, the science, and government reactions to the problem.  In particular, the article shows the very different approaches the states of Texas and Oklahoma have taken to the problem.  And I regret to say it doesn't make my native state of Texas look good by comparison.  But first, the basics.

As I wrote in this space in 2013, water-injection wells to dispose of the brackish water that comes up sometimes along with oil and gas are nothing new.  But the combination of fracking to extract fossil fuels from previously inaccessible formations, horizontal drilling to gain wider access to those formations, and the boom of widespread deployment of these techniques that has gone on in the last six or eight years, have led to a huge increase in the volume of water injected back deep underground.  During 2014, in Texas a gallon of water was injected back into the ground for every 100 or so cubic feet of shale gas extracted.  That may not sound like much, but Texas produced about 4 trillion (4,000,000,000,000) cubic feet of shale gas that year.  Leave off two zeroes and that's how many gallons of water were injected back into the ground.  And that ratio probably holds true more or less for the rest of the country as well.

Wastewater injection from fracking doesn't always cause earthquakes.  North Dakota has had a lot of fracking and wastewater injection too, but hardly any earthquakes.  On the other hand, Oklahoma, a place that was hardly famous for earthquakes before 2005, had 581 temblors of magnitude 3.0 or greater in 2014.  Its most severe one recently happened in November 2011, when a 5.6-magnitude quake wrecked more than a dozen houses and injured a couple of people.  Less severe but just as widespread quakes have been happening in North Texas, where the Barnett Shale has been exploited for natural gas in a big way, and injection wells are operating there too.

Because of the huge volumes of wastewater to deal with, oil and gas producers don't have too many options that won't make their operations too expensive to carry out.  Treating the water to extract the salt and other minerals would mean distilling it, a hugely costly process that would turn them all into water-purification plants with an unprofitable sideline of making oil and gas as a byproduct.  So that's not an option.  Trucking it to a place where injecting it wouldn't cause earthquakes would be expensive, even if we knew of a nearby place where injecting it wouldn't cause earthquakes.  And just throwing it out on the ground, which used to be a common practice in the bad old days before 1950 or so, would cause huge amounts of waterway pollution because of the salts, radioactivity, and other nasty stuff that comes up with the water.  So going to the expense of drilling wells typically much deeper than the producing ones and injecting the wastewater downhole at tremendous pressures is the only thing that producers can typically do with it.

The trouble is, rocks are porous—that's the only way you can inject water into them in the first place.  So that high-pressure water starts to move, and seeps toward faults, which are just big cracks between intact blocks of rock.  Some faults are under shear stress.  To envision shear stress, think of holding two old-fashioned chalkboard erasers together face to face and rubbing them back and forth across each other.  It's shear stress you put on them that makes them slide.  If you mash the erasers together perpendicularly, putting them under compressive stress, it's a lot harder to get them to move with shear stress.  So a fault that is under shear stress won't slip and cause an earthquake as long as the compressive stress is great enough.

Then along comes your water injection at high pressure.  It seeps through the pores to the cracks and provides an opposing pressure that can counteract the compressive stress that's keeping the fault from slipping.  We're not talking lubrication here, but large opposing mechanical forces.  I'm sure the technical details involve stress tensors and the whole nine yards of solid mechanics, but the basic picture is simple.  When the fluid pressure exceeds a certain threshold, that fault is going to let go, and you've got an earthquake.  People have even done experiments in the field to figure out exactly how much stress makes the faults slip, and there is a definite threshold, just as theory predicts.

Both from mechanical analyses and statistical studies, as well as abundant seismological data correlating particular regions of earthquake activity with particular injection-well activity, by now it is clear to all but the most biased observers that, generally speaking, the injection-well activity has caused the increase in earthquakes in both Texas and Oklahoma.  The U. S. Geological Survey, which has been issuing long-range earthquake predictions by region for some time now for the convenience of structural engineers, insurance companies, and other interested parties, has had to revise its forecasts for Oklahoma and Texas sharply upward in the last few years.  A contour map of earthquake likelihood for Oklahoma now looks like an archery target with Oklahoma City in the bullseye.  And the scientific literature abounds with studies showing details of the correlation.

Oklahoma has a long tradition of assertive state government, dating back to the 1930s when it passed laws regulating things like the price of ice.  And they have now continued that tradition by shutting down individual wells since 2015 and regulating the volume of wastewater that can be injected.  On the other hand, the Texas agency in charge of oil and gas regulation (for historical reasons, it's called the Texas Railroad Commission) still has not been able to bring itself to admit that any earthquakes have been triggered by water injection associated with fossil-fuel production.  But recently the Commission asserted its right to shut down wells if it wants to.  So far, though, it hasn't wanted to.

To some degree, all this is water under the bridge, or well, as the case may be.  Oil and gas markets are glutted right now, and the consensus is that the big fracking boom is over, at least in Texas and Oklahoma.  But all that injected water is still down there, slowly diffusing, and some geologists estimate that the effects of water injection on earthquakes can last as long as twenty years.  So in that sense, we may be dealing with the aftershocks of the fracking boom for some time.

Sources:  Anna Kuchment's article "Drilling for Earthquakes" appeared in the July 2016 print issue of Scientific American, pp. 46-53.  I also referred to a U. S. Department of Energy table of shale-gas production available at https://www.eia.gov/dnav/ng/ng_prod_shalegas_s1_a.htm.  I blogged on earthquakes and fracking most recently on Dec. 30, 2013.

Is Fracking Shaking Up Azle?

Although Texas has had its share of both natural and man-made disasters, earthquakes are not something most Texans worry about much.  The geology of much of Texas is more or less flat limestone layers left over from the time when a giant sea covered much of the state.  We are pretty far away from the edges of tectonic plates, unlike places such as the west coast of the U. S., where earthquakes are a constant threat.  So when the small North Texas town of Azle had an earthquake a year or two ago, it was an unusual event.  It was a small one, but more and more followed.  In the month-long period ending today (Dec. 29), Azle has had ten earthquakes large enough to be noted by the website earthquaketrack.com, whose data comes from the United States Geological Survey.  The smallest was magnitude 2.8 and the largest was 3.6, which is enough to rattle windows and cause minor structural damage. 

This would be simply a matter of scientific curiosity were it not for the possibility that these earthquakes, as well as similar ones in other parts of Texas and the U. S., are related to oil- and gas-drilling activity.  Specifically, the process called "fracking" involves sending lots of water treated with chemicals down a potential oil or gas well, then pulling it out again and disposing of it in underground injection wells that are deep enough so the injected fluids don't mix with groundwater.  At least, that is the intention.

Drillers have done fracking for many years, and according to a website operated by the U. S. Environmental Protection Agency, Texas has over 52,000 Class II injection wells, which are typically the type used by fracking operations.  But only in the last five to ten years has fracking become a widespread practice near populated areas of North Texas, where the Barnett Shale formation has become the focus of intense exploration and drilling.  In the interests of full disclosure, my father-in-law received some money for mineral rights related to drilling near his former home in Fort Worth, which he no longer owns.  And my sister lives in Cleburne, some 30 miles south of Fort Worth, which has experienced a few earthquakes of its own in recent months.  Cleburne is near a lot of fracking activity and injection wells too.

Suppose there is a connection between shoving lots of water underground and triggering earthquakes:  what then?  Is this a matter of engineering ethics concern?  I would certainly think so.

The parties most directly involved are (1) the oil and gas drillers, (2) the people living in areas subject to these strange earthquakes, (3) the organizations paying for and benefiting from the drilling, (4) local, state, and federal regulatory authorities, and (5) the general public, which is not directly affected by the earthquakes, but benefits in some way from increased domestic supplies of fossil fuels, and is possibly harmed by the general increased risk of earthquakes in the future.  But identifying the concerned parties is only the first step.

From a legal point of view, the situation is extremely fuzzy.  Although there have not historically been a lot of Texas earthquakes, there were enough for U. T. Austin geology professor Cliff Frolich and his colleague Scott Davis to write a book about them in 2002.  I have read that book, and the impression I got was that Texas is not under any existential threat from a "big one" like California is due for.  Rather, there are lots of little faults here and there, and every so often one of them gets tense enough to snap, like a third-grade teacher the day before Christmas vacation.  Frolich wrote a report back in 2009 on a cluster of earthquakes near Cleburne, where he confirmed that numerous injection wells had been operating.  After installing a special array of seismographs, he detected even more earthquakes than the standard USGS network did, and in the abstract of the report he stated, "A plausible hypothesis to explain these observations is that injection only triggers earthquakes if injected fluids reach and relieve friction on a suitably oriented, nearby fault that is experiencing regional tectonic stress."  What he's saying in ordinary English is something like this:  Earthquake clusters are like doors that have both a lock and a key.  The lock is the local conditions of stress and orientation that make the fault ready to let go, and the key is the water coming in from the injection wells.  When the key fits in the lock, the door opens and in comes an earthquake.

Seismic data on earthquakes is easy to come by; besides the USGS data, there are other online databases and the information is relatively easy to find and read.  The question of where injection wells are and how much fluid is injected is a harder one to answer, although the Texas Railroad Commission (named that for historical reasons), which is the state regulatory agency for oil and gas drilling, has a database on injection wells that will yield such information to diligent inquiry.  I diligently inquired for about five minutes this morning and turned up a bunch of wells across Eagle Mountain Lake from Azle, but nothing right in the town.  But maybe Azle sits on the lock, and the key flowed under the lake from the other side, so to speak.

I'm no geologist, or lawyer either.  If Azaleans (or whatever you call citizens of Azle) get tired of being shaken awake at 2 A. M. and organize a class-action lawsuit, their lawyers would have a rocky road to travel (so to speak) in order to prove to the satisfaction of a civil-trial jury that such-and-such injection wells directly caused so-and-so earthquake.  The only similar legal issue I can think of would be a lawsuit concerning structural damage caused by dynamiting for quarries and similar purposes.  In those types of cases, all the plaintiff has to show is that at Time A before the blast, the damage wasn't there, and right afterward at Time B it was, and usually it's easy to show that because the physics of shock propagation is pretty well known and hard to argue against in court. 

That is far from the case for these earthquake clusters.  In defense of their practices, fracking drillers state correctly that they have been doing fracking for many years in Texas and elsewhere, and nobody much noticed any earthquake clusters back then.  My own guess is that they just happened to be fooling around with keys where there weren't any locks.  But now that the fracking activity is so visible near populated areas such as the Dallas-Fort Worth area, people have begun to notice the clusters and start putting two and two together. 

So far, no one has been seriously injured or killed in a recent Texas earthquake cluster in areas where injection-wells are suspected as the cause.  As long as the damage remains minor, the general good will enjoyed by the oil and gas industry in Texas will probably continue, especially if they keep spreading around those royalty payments of a thousand dollars or so to anyone in the neighborhood of an active well.  But if we get a seriously bad earthquake that results in injuries or deaths near a place where injection wells are operating, watch for the legal and regulatory picture to change fast.  For my sister's sake, as well as the fracking industry, I hope that never happens.

Sources:  The book Texas Earthquakes by Cliff Frolich and Scott Davis was published in 2002 by the University of Texas Press.  An abstract of Prof. Frolich's report on the Cleburne earthquake cluster is accessible at http://www.pnas.org/content/early/2012/07/30/1207728109.abstract.  The EPA website with statistics on Class II injection wells can be found at

http://water.epa.gov/type/groundwater/uic/wells.cfm. I referred to articles in a Russian news website on the Azle earthquakes, published at

http://rt.com/usa/texas-fracking-earthquakes-azle-445/

and data on the Azle earthquakes from the earthquake website

http://earthquaketrack.com/us-tx-azle/recent.  I also referred to the Wikipedia article on Azle.