A rash of earthquakes in southern Colorado and northern New Mexico between 2008 and 2010 was likely due to fluids pumped deep underground during oil and gas wastewater disposal, according to a study from Colorado University Boulder.
The study, which looked at the 2,200-square-mile Raton Basin along the central-Colorado northern New Mexico border, found more than 1,800 earthquakes up to magnitude 4.3 during that period, linking most of the quakes to wastewater injection well activity.
The wells are used to pump water back in the ground after it has been extracted during the collection of methane gas from subterranean coal beds.
A key piece of the study was the use of hydrogeological modeling of pore pressure in what is called the “basement rock” of the Raton Basin, which is rock that is several miles deep. Pore pressure is the fluid pressure within rock fractures and rock pores.
While previous studies have linked earthquakes in the Raton Basin to wastewater injection wells, this is the first to show that elevated pore pressures deep underground are well above earthquake-triggering thresholds, according to CU Boulder doctoral student Jenny Nakai, lead study author.
“We have shown for the first time a plausible causative mechanism for these earthquakes,” said Nakai of the Department of Geological Sciences. “The spatial patterns of seismicity we observed are reflected in the distribution of wastewater injection and our modeled pore pressure change.”
Nakai said the research team did not look at the relationship between the Raton Basin earthquakes and hydraulic fracturing or fracking.
The new study also showed the number of earthquakes in the Raton Basin that correlate with the cumulative volume of wastewater injected in wells up to about 9 miles away from the individual earthquakes. There are 28 “Class II” wastewater disposal wells—wells that are used to dispose of waste fluids associated with oil and natural gas production—in the Raton Basin and at least 200 million barrels of wastewater have been injected underground there by the oil and gas industry since 1994, according to the study.
The earthquake patterns in the Raton Basin are similar to other U.S. regions that have shown “induced seismicity” likely caused by wastewater injection wells, said Nakai. Previous studies involving CU Boulder showed injection wells likely caused earthquakes near Greeley, Colo., in Oklahoma and in the mid-continent region of the U.S. in recent years.
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