The Colorado Oil and Gas Conservation Commission (COGCC) on Tuesday ordered operation of a wastewater disposal well to cease temporarily while recent seismic activity in Weld County is assessed to determine whether there is a link to the well.
High Sierra Water Services agreed to a 20-day halt to its wastewater injection as "a cautionary step" is taken to gather and analyze seismic information. Ongoing monitoring by University of Colorado (CU) seismologists picked up additional evidence of low-level seismic activity near the injection site, including a 2.6 magnitude quake last Monday, a COGCC spokesperson said.
The additional data follows a 3.4 quake that was felt in the Greeley area May 31. Since that occurrence, CU geophysics professor Anne Sheehan and some graduate students have deployed five seismic measuring devices around the epicenter (see Shale Daily, June 12).
"In light of the findings [Monday] of the CU 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," said COGCC Director Matt Lepore.
Lepore cautioned that the disposal activity halt does not mean the state is concluding that the seismic activity was caused by the injection work. He called the halt "a prudent thing to do," along with further review. "We are not making yet a causative determination," he told local news media
Options following the COGCC review include resuming injection at a reduced volume, ramping up the injection and continuing to monitor it closely, and if a causative relationship is established, shutting the well, Lepore said.
During the pause in disposal well activity at the Weld County site, regulators plan to evaluate baseline and historical seismic activity; coordinate with the university team and state/national geological survey units; evaluate other disposal wells in the area; and review other data associated with the injection well in question.
Historically, the first work on induced quakes was done in the 1960s in Colorado related to deep water injection by the U.S. military at the Rocky Mountain Arsenal, Sheehan said. More recently, in the Paradox Valley in Colorado, there were some deep water injection-related quakes tied to a water reclamation project in the 1990s.
Exploration and production wastewater injection at well sites has been linked as possibly part of an uptick of small quakes in at least three other states, Oklahoma, Ohio and Texas (see Shale Daily, May 6).