SAN FRANCISCO – The deep injection of wastewater underground is responsible for the dramatic rise in the number of earthquakes in Colorado and New Mexico since 2001, according to a study to be published in the Bulletin of the Seismological Society of America (BSSA).
The Raton Basin, which stretches from southern Colorado into northern New Mexico, was seismically quiet until shortly after major fluid injection began in 1999. Since 2001, there have been 16 magnitude > 3.8 earthquakes (including M 5.0 and 5.3), compared to only one (M 4.0) the previous 30 years. The increase in earthquakes is limited to the area of industrial activity and within 5 kilometers (3.1 miles) of wastewater injection wells.
In 1994, energy companies began producing coal-bed methane in Colorado and expanded production to New Mexico in 1999. Along with the production of methane, there is the production of wastewater, which is injected underground in disposal wells and can raise the pore pressure in the surrounding area, inducing earthquakes. Several lines of evidence suggest the earthquakes in the area are directly related to the disposal of wastewater, a by-product of extracting methane, and not to hydraulic fracturing occurring in the area.
Beginning in 2001, the production of methane expanded, with the number of high-volume wastewater disposal wells increasing (21 presently in Colorado and 7 in New Mexico) along with the injection rate. Since mid-2000, the total injection rate across the basin has ranged from 1.5 to 3.6 million barrels per month.
The authors, all scientists with the U.S. Geological Survey, detail several lines of evidence directly linking the injection wells to the seismicity. The timing and location of seismicity correspond to the documented pattern of injected wastewater. Detailed investigations of two seismic sequences (2001 and 2011) places them in proximity to high-volume, high-injection-rate wells, and both sequences occurred after a nearby increase in the rate of injection. A comparison between seismicity and wastewater injection in Colorado and New Mexico reveals similar patterns, suggesting seismicity is initiated shortly after an increase in injection rates.
… “These earthquakes are limited to the area of fluid injection, they occur shortly after major fluid injection activities began, and the earthquake rates track the fluid injection rates in the Raton Basin,” the paper said, noting the scientists’ comparisons of the timing and location of earthquakes with the timing and location of injected wastewater. By the mid-2000s, Colorado’s wastewater injection rates were up to 1.9 million barrels per month.
Taking that and the unexpected frequency of the earthquakes into consideration, the paper noted that it was “highly unlikely” that the quakes could have been due to any random fluctuations underground …
… The U.S. government announced back in May that it would begin to track the risks that so-called “frackquakes” pose, and start including them on official maps that help influence building codes. Before then, the USGS had never taken man-made earthquakes into account during its regular quake mapping activity. It made the decision to do so after finding that two strong earthquakes in heavily-drilled areas of Colorado and Oklahoma in 2011 might have been the result of wastewater injection. “For future research, a longer-term study with dense network coverage on both sides of the border would be especially useful in understanding the inducing relationship between the earthquakes and fluid injection in the Raton Basin” …
… These quakes are usually too small to be felt, but scientists have warned that they stand to get stronger as more wastewater injection happens — a likelihood considering the growing expansion of fracking.