Frack Quakes? Can hydraulic fracturing really cause earthquakes?
An earthquake that measured 4.0 on the Richter scale occurred near Youngstown, Ohio on New Year's Eve. In the weeks before, several smaller earthquakes had occurred. Many journalists have erroneously reported that scientists and state officials believe that hydraulic fracturing might have caused the earthquake. Actually, the scientists and officials believe that the earthquake might have been caused by the operation of an injection disposal well, not by hydraulic fracturing. Injection disposal and hydraulic fracturing are two different processes. The journalists might have been confused by the fact that the disposal wells at issue happened to be used for disposal of wastewater from hydraulic fracturing operations, but that was mere coincidence. Injection disposal wells are used to dispose of a variety of fluids. Further, oil and gas operators sometimes dispose of fracturing wastewater by means other than underground injection.
Nevertheless, the question whether hydraulic fracturing can cause earthquakes is a legitimate question. This post discusses two issues: (1) whether underground injection disposal can cause earthquakes; and (2) whether hydraulic fracturing can cause earthquakes.
Underground injection wells are regulated under the Safe Drinking Water Act. The Environmental Protection Agency reports that about 550 to 800,000 underground injection wells exist in the United States. Some of these are used for underground storage of fluids, including natural gas and oil. For example, the Strategic Petroleum Reserve is an example of a facility that stores oil underground. But most underground injection wells are used for the underground disposal of waste fluids. An injection disposal well might be used for years, and may receive hundreds of million gallons of waste fluids.
For several decades, many geologists have believed that the operation of injection disposal wells can cause earthquakes in certain circumstances in areas that already are prone to earthquakes. Scientists refer to man-made earthquakes as examples of "induced seismicity." One of the best known examples arises from the United States Army's operation of an injection disposal well at the Rocky Mountain Arsenal in Colorado during the 1960s. The Army disposed of approximately 165 million gallons of waste fluids in the well from 1962 through 1966 at a depth of approximately 12,000 feet. The Army quit using the well in early 1966 because geologists believed that fluid injections at the site were the cause of a series of earthquakes.
More recently, researchers and officials have suggested that earthquakes occurring near the Dallas-Fort Worth airport in 2009 and a large number of mostly small earthquakes (an earthquake "swarm") near Guy, Arkansas in late 2010 through early 2011 might have been caused by injection disposal wells. In addition, geologists also studied the possibility that underground injection wells caused a series of earthquakes that occurred near Trinidad, Colorado in 2001, but they did not reach a definitive conclusion. Their report stated that circumstances "do not rule out the possibility of the Trinidad earthquakes being induced, but neither do they make a strong case for the Trinidad shocks being induced."
Geologists also believe that the injection of water for enhanced recovery operations can cause earthquakes, and their belief is supported by a study of earthquakes occurring near Rangely, Colorado in the 1970s.
Because the earthquakes that are suspected of being caused by human activity occur only where geological faults and the possibility of earthquakes already exist, scientists have difficulty definitively linking seismic activity to underground injections. But many geologists believe that evidence strongly supports the theory that human activity can induce earthquakes. The type of evidence geologists examine in evaluating whether earthquakes might have been caused by underground injections include the distance between an underground injection point and the epicenter of an earthquake, and the timing of earthquakes relative to injection activity. Geologists have suggested that society's use of underground injection disposal wells need not stop, and that risk can be minimized by halting or decreasing the rate of injections when particular injection wells are believed to have caused small earthquakes.
Geologists are less confident about a link between hydraulic fracturing and earthquakes than they are about a link between injection disposal wells and earthquakes. Part of the reason for this is that a much smaller amount of fluid typically is injected during hydraulic fracturing than is injected in underground disposal operations. Also, a hydraulic fracturing operation lasts for days, while an underground disposal well might operate for years. Nevertheless, some geologists believe that fracturing can cause earthquakes, though generally only very small quakes.
The Oklahoma Geological Survey recently produced a report that found a possible correlation between fracturing activity and a series of earthquakes in that state, but the correlation was not definitive. The report concluded that "uncertainties in the data make it impossible to say with a high degree of certainty whether or not these earthquakes were triggered by natural means or by the nearby hydraulic-fracturing operation." As noted by the U.S. Geological Survey, "[e]arthquakes are not unusual in Oklahoma." Thus, the earthquakes may have had a natural origin.
Another case study comes from Britain, where Caudrilla Resources was using hydraulic fracturing to produce natural gas from a shale formation in Lancashire. An earthquake that measured 2.3 on the Richter scale, occurred on April 1, 2011. Another quake, which measured 1.5 on the Richter scale, occurred on May 27, 2011. A group of experts from across Europe studied the two earthquakes. They concluded that it was "highly probable" that fracturing had caused the earthquakes, but that an "unusual combination of factors" that they said was unlikely to occur again had been necessary in order for fracturing to cause the earthquakes. They estimated that, in the unlikely event that the factors did recur, the "worst-case scenario" was an earthquake with a maximum strength of 3.0 on the Richter scale.
Concluding Thoughts and References for Additional Reading
Geologists generally accept the idea that human activity, including the operation of injection disposal wells, can cause earthquakes in certain circumstances in areas that already have geological faults and the possibility of earthquakes. Geologists have suggested that our society need not stop using injection disposal wells, and that any danger can be minimized by halting or slowing underground injections when small earthquakes begin to occur. It is not as widely accepted that hydraulic fracturing can cause earthquakes, but some geologists believe that hydraulic fracturing can cause small earthquakes in some circumstances.
For further reading, see Earthquake Hazard Associated with Deep Well Injection — A Report to the U.S. Environmental Protection Agency (1990, 74 pages), We Don't Have Earthquakes in Colorado, Do We? (April 2002 newsletter of the Colorado Geological Survey's Division of Minerals and Geology), a page on the U.S. Geological Survey website that asks "Can We Cause Earthquakes?," the Executive Summary of the report on the earthquakes in Lancashire (the full report, plus multiple appendices are available at the news page of the Caudrilla Resources website), a news story entitled SMU-UT Study Finds 'Plausible' Connection Between DFW Quakes and Saltwater Injection Well, and an order of the Arkansas Oil & Gas Commission placing a moratorium on injection disposal wells in a particular area after finding "[b]ased upon the studies of the Arkansas Geological Survey" that there is"no evidence" that hydraulic fracturing caused a series of earthquakes in Arkansas, but that there is "circumstantial evidence" that injection disposal wells might have been causing seismic activity.