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WELD COUNTY — Results determining whether injection wells are causing earthquakes in Weld County were inconclusive.
Consequently, officials last week offered a compromise decision regarding the operation of a wastewater injection well near Greeley, temporarily shut down and investigated in late June following three separate cases of seismic activity within a month.
According to a July 17 press release from Todd Hartman, of the Department of Natural Resources, and Matt Lepore, of the Colorado Oil and Gas Conservation Commission, owners of the Weld County injection well were required to make “changes to the well and adjust disposal activities” before they resumed operations June 18. Those changes include shortening the depth of the well about 400 feet and lowering the amount and pressure of wastewater injections.
Commission officials on June 24 ordered NGL Water Solutions, operators of a wastewater injection site located in the “general vicinity” of a series of seismic occurrences near Greeley, to halt operations for at least 20 days, pending further investigation. Those investigations were spurred not only by the 2.6-magnitude earthquake June 23, but also by another, 3.2-magnitude earthquake May 31. The May quake was followed days later by another, low-level seismic event.
All three seismic occurrences were recorded by a team of University of Colorado seismologists, who later worked with officials to investigate the cause.
Following the June 23 quake, the commission ordered operations to be halted while they analyzed information “to determine whether injection at the site is tied to recent seismic activity recorded within the general vicinity of the well.”
“In light of the findings of CU’s team, we think it’s important we review additional data, bring in additional expertise and closely review the history of injection at this site in order to more fully understand any potential link to seismicity and use of this disposal well,” Lepore said June 24.
According to the July 17 release, researchers found the quakes were “potentially related” to NGL’s disposal activities.
“Since the shutdown, (the commission) has further analyzed data associated with the injection well (and) seismic data recorded by a local network of instruments placed and maintained by CU geophysicists,” the report read. “While seismic activity in the area around the well continued during the shutdown period, it occurred at a lower energy level, according to the CU researchers.
“Flow rate tests conducted by NGL indicated a high permeability zone near the bottom of the well that created a preferred pathway for injected water,” the report continued. “As a result of that finding, NGL, with approval and oversight from (the commission), has plugged the basement of the well from … 10,770 feet to 10,360 feet in order to seal off the preferential pathway and to increase the distance between the zone of injection and ‘basement’ rock. These measures are expected to mitigate the potential for future seismic events.”
The commission said NGL was allowed to resume “limited injections at lower pressure and lower volumes, under continued seismic monitoring.” Operators can resume injections of no more than 5,000 barrels per day at a max pressure of 1,512 psi, the release read, and can up the amount to 7,500 barrels a day after 20 days, so long as there is not more seismic activity within 2.5 miles and over 2.5 magnitude.
NGL was also required to install a seismometer near the well to allow for real-time monitoring.
“We are proceeding with great care, and will be tracking activities at this site closely,” Lepore said. “We’re moving slowly and deliberately as we determine the right course for this location.”
The commission said it is also reviewing NGL for a possible violation of the operator’s injection volumes, but no charges or citations had been issued as of the date of the press release. If the company is found to have violated those limits, they could face “financial penalties.”
The well, known as SWD C4A, is located east of the Greeley-Weld County Airport and was permitted in March 2013. Injections began a month later.
Matt Morgan, senior research geologist with the Colorado Geological Survey, said the May 31 earthquake about four miles northeast of Greeley was the third-largest northeastern Colorado quake on record. On May 26, 1969, a 4.2-magnitude event was recorded about 15 miles east of Greeley.
A January 2011 report from the Colorado Oil and Gas Conservation Commission indicated a series of earthquakes in the 1960s were linked to a 12,000-foot injection well drilled at the Rocky Mountain Arsenal near Denver. That well was drilled in March 1962 and followed by a series of quakes from 1963 to 1967. When the well was shut down in 1968, the seismic activity ceased.