Last week, I was able to attend a short course on hydraulic fracturing and earthquakes. Hydraulic fracturing, colloquially known as fracking, involves pumping vast amounts of water deep into the ground to extract natural gas. The process has been around for more than 50 years, but it has recently become much more widespread, particularly in Oklahoma.
Three individuals spoke at the course, representing industry, consulting, and academia, and their message was consistent.
Fracking and Quakes
Fracking, all by itself, does not cause earthquakes. We looked at the number of fracking wells and the location of the earthquakes in Oklahoma, and there was no direct correlation. Data below was provided from the Oklahoma Geological Survey through the University of Oklahoma:
However, as noted above, we did see clusters of quakes in several places in Oklahoma. These are locations where faults are already in place, but do not have much dynamic pressure. They are not dormant, but there is not enough ambient pressure on them to move, so earthquakes are not naturally common.
Earthquakes can be triggered by forcibly changing the load on the faults (i.e. shifting the weight). This can be done by building a reservoir (water is heavy), changing temperatures below ground, or increasing the internal pressure within the rocks (pore pressure). The pore pressure is where fracking comes in.
The water from the wells that is forced into the ground, typically at 6000-10,000 pounds per square inch, is absorbed into the rock as well as diffusing into the fault. This changes the stress on the fault, triggering an earthquake.
While some of these quakes are large enough to be felt, the effects are usually limited to shaking intensity IV. This level of intensity correlates closely (but not perfectly) to a Magnitude 4.0. The vast majority of the quakes, however, are substantially weaker, and largely imperceptible during day-to-day activities.
According to the Modified Mercalli Intensity Scale provided by the US Geological Survey, shaking intensity IV is:
Felt indoors by many, outdoors by few during the day. At night, some awakened. Dishes, windows, doors disturbed; walls make cracking sound. Sensation like heavy truck striking building. Standing motor cars rocked noticeably.
Just how bad can one of these induced quakes get? The ideas fall into two camps, which was seen on this slide at the session:
When done correctly, fracking does not appear to affect underground water supplies, and we did not discuss the reports of natural gas leaking into water supplies.
However, what happens in the real world? There are lots of variables in place. Are shortcuts taken by the rank and file when these wells are drilled, either with, or without a supervisor’s notice?
Below is another video demonstrating the risks.
Both of the above videos were suggested to us by those running the short course.
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Finally, The National Research Council has its say:
So it would seem that fracking is not going to destabilize the earth’s crust and cause phenomenal earthquakes, but the process is not without some risk. From our notes:
It can be difficult to say with any certainty whether seismic activity in a given area is only caused by industry activity or natural causes, especially if seismic monitoring data is limited.
While predicting earthquakes is an attractive proposition, there has been no progress in making in skillful predictions. It is just too difficult to get the level of data necessary to make an educated guess. As the slide below suggests, don’t expect any progress toward it anytime soon.
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The course had several sponsors:
American Meteorological Society, Incorporated Research Institutions for Seismology, National Science Foundation, Oklahoma Geological Survey, and R.M. Habiger Consultants LLC.