Deep wastewater injection from the oil/natural gas sector is most likely responsible for the sharp increase in the number of small earthquakes recorded since 2001 in the Colorado-New Mexico border area, according to a study published in the Bulletin of the Seismological Society of America (BSSA).
Focused on the Raton Basin along the southern Colorado and northern New Mexico border, the region was said to be "seismically quiet" prior to 1999, when wastewater injection was introduced to the area, the BSSA article's four co-authors wrote. A 5.3-magnitude quake that hit Colorado in 2011 was likely caused by wastewater injection tied to nearby natural gas drilling, the authors said.
The authors, all scientists with the U.S. Geological Survey (USGS), outline evidence that they contend points to a direct link between injection wells and the seismic activity. For example, they show that the timing and location of seismicity corresponds to the documented sequence of wastewater injection in the area.
The scientists said that from 2001 through 2013 there were 16 quakes of 3.8-magnitude or greater in the Raton Basin. For 30 years prior to that period (1972 through 2001), the area recorded one quake of that magnitude.
One of the BSSA co-authors, Arthur McGarr, said "the evidence is a lot more abundant" that recent quakes have been man-induced rather than naturally occurring.
"Beginning in 2001, the production of methane expanded with the number of high-volume wastewater disposal wells increasing (21 presently in Colorado and seven in New Mexico) along with injection rates," said a BSSA spokesperson. "Since mid-2000, the total injection rate across the basin has ranged from 1.5 to 3.6 million barrels [of wastewater] per month."
The spokesperson said the USGS scientists' lines of evidence show that earthquakes in the area are directly related to the wastewater injections, and not hydraulic fracturing.
Earlier this year, a University of Colorado geophysics professor and a group of her graduate students deployed five seismic measuring devices around the epicenter of a 3.4-magnitude quake that struck May 31 near Greeley, CO in Weld County in the northeastern part of the Denver Julesburg (DJ) Basin (see Shale Daily, June 12).