Monday, September 26, 2016

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. Gonz├ílez, 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.

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