Investigators also eye possible permit violations at Weld County site
FRISCO — State regulators have reauthorized operations at a Weld County wastewater injection well after determining that the well may be linked with earthquakes in the area. State officials will also investigate whether the well operators violated their permit by pumping too much drilling sludge into the well.
“We are proceeding with great care, and will be tracking activities at this site closely,” said Matt Lepore, director of the Colorado Oil and Gas Conservation Commission. “We’re moving slowly and deliberately as we determine the right course for this location,” Lepore said, explaining that new limits on the well are aimed easing the potential for more earthquakes.
Testing at the site showed that injected fluids were not contained in a stable geological formation. Instead, the wastewater found a permeable layer. From now on, the fluids won’t be injected quite as deep. The new limits will seal off the preferential pathway and increase the distance between the zone of injection and “basement” rock. These measures are expected to mitigate the potential for future seismic events.
On June 23, the COGCC directed NGL Water Solutions DJ LLC* to stop disposing wastewater into the well for a 20-day period while the agency worked with the operator and a team of University of Colorado researchers to determine whether deep injection at the site may be tied to recent seismic activity detected within the general vicinity. Following a 3.2 magnitude event on May 31, seismometers placed by CU recorded other small earthquakes, including one of magnitude 2.6 on June 23.
Since the shutdown, the COGCC has further analyzed data associated with the injection well, as well as seismic data recorded by a local network of instruments placed and maintained by CU geophysicists. 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.
Beginning Friday, July 18 the COGCC will allow NGL to resume limited injections, at lower pressures and lower volumes, under continued seismic monitoring, to ensure the facility is operating safely. Specifically, the operator will be permitted to inject at an initial maximum rate of 5,000 barrels per day with a maximum pressure of 1,512 psi. After 20 days, the maximum injection rate may be increased to 7,500 barrels a day at the same pressure.
Continued use of the injection well will be reviewed and may be halted if seismic events within a 2.5-mile radius of the well occur at or above a magnitude of 2.5 – the U.S. Geological Survey’s default threshold for displaying seismic events. CU geophysicists will continue to monitor the location, and the COGCC has required NGL to install a permanent seismometer near the well to allow for real-time monitoring. The company is also required to provide access to the monitor and all its data to the COGCC and any third parties authorized by the agency.