What’s in this article?
• The revolution that is shale gas and shale oil.
• Do fracs contaminate surface water?
• Disposal wells…..and earthquakes.
The revolution that is shale gas or shale oil has been successful because many frac treatments are pumped one at a time along the length of a long horizontal well (typically a mile long). Most of these horizontal wells are a mile deep, or deeper. This new technology has opened up enough conduits in the shale to get the gas out fast enough to make a profitable well. The revolution took off around the year 2000 in the Barnett shale close to Fort Worth, Texas (at least one well has even been drilled under the Dallas-Fort Worth airport). This article builds on a previous article, called Some Truths about Fracking, Part 1 (click on the link to see the article).
Disposal wells. After fracking, when a well is turned on to production some of the water produced is frac water and some is water that was originally in the shale. A lot of water is used for fracking a long horizontal well in shale (typically several million gallons – enough to cover a football field to a depth of about ten feet). Therefore a lot of frac water is later pumped out of a producing well along with gas or oil. Apart from surface disposal of the water, which is regulated and monitored by state environmental departments, there is underground disposal down specially designed wells.
If a lot of disposal wells receive water at the same time, this may lead to a buildup of pressure over an area large enough to induce minor earthquakes. The minor earthquakes have magnitude 3-4 on the Momentum scale. These quakes can be felt at the surface of the earth, but cause no damage. Until 2011, no earthquake induced by liquid disposal had caused significant injury or damage even though 140,000 disposal wells had operated safely in the US for decades.
Disposal wells…..and earthquakes.
But after 2011 things started to change**, ***. First, the frequency of induced earthquakes increased suddenly (see image showing spike in earthquakes). Second, the magnitude of some of the earthquakes also increased (see second image with red dots).
• The entire increase in earthquake rates in Texas and nearby states was associated with liquid disposal wells.
• Wells that inject more than 300,000 barrels of wastewater per month, known as high-rate injection wells, caused much more ground shaking.
• The Barnett Shale has one of the highest concentrations of active disposal wells in the USA, with some areas in the basin containing five wells per two-square-mile area.
• Researchers at Stanford University found that tremors were often located miles away from any wells and separated from peak liquid injections by several months, or even years.
• Over time pressure from continuous liquid injections builds up within the fractures and pores of rock. Eventually, that pressure can spread to faraway faults and nudge them apart, causing earthquakes.
• Note that a magnitude 6-7 earthquake, which is 1,000 times more powerful than magnitude 3-4, can cause serious structural damage at the earth’s surface (walls cracking and collapsing).
What can be done?
Guidelines have been proposed and steps are being taken for reducing the likelihood of earthquakes:
• Measure any seismic activity near disposal wells, then limit the injection of water into disposal wells if/when earthquakes are first observed.
• Oil companies are actively trying to invent fracking schemes that use much less, or no water, and therefore mean less produced water has to be disposed.
• Companies are looking for new ways of disposing of wastewater. You can dispose of the stuff in a different well, or you can take it to a fluid treatment plant (more expensive).
• Before proposing new disposal wells, investigate at the site (1) history of earthquakes and (2) proximity to fault lines.
Conclusion: in shale-gas or shale-oil wells, micro-earthquakes induced by the fracking operation are not felt at the surface and are non-damaging, and frac liquids do not come to surface unless the well was poorly cemented. But a few earthquakes induced by injecting large quantities of liquid (some from fracking) in disposal wells are serious, and have caused minor damage in surface buildings. So direct fracking in production wells is safe. But heavy injection of wastewater into disposal wells can be unsafe, and regulations need to be developed to prevent further incidents.
Comments? Your comments are always encouraging. Please add them to the Comment box at the bottom of the blog.
The Gray Nomad
Probing the practice of Christian believers……
** Weingarten et al., Science 348:1336 (2015)
*** Walsh et al., in Science Advances, June 2015
Then a great and powerful wind tore the mountains apart and shattered the rocks before the LORD, but the LORD was not in the wind. After the wind there was an earthquake, but the LORD was not in the earthquake. After the earthquake came a fire, but the LORD was not in the fire. And after the fire came a gentle whisper. When Elijah heard it, he pulled his cloak over his face and went out and stood at the mouth of the cave. (Book of 1 Kings, chapter 19).
Please share this blog with your friends.
If you know someone who would like to receive these two-weekly blogs, please send their email request to me at firstname.lastname@example.org