A limited operations, also is investigating the company for potentially violating its limits on volumes on the well.
“We’ve been working closely with COGCC throughout all of this, and we don’t believe we’re in violation of any operations of our wells,” said Doug White of NGL. “So we’re continuing to work with them through their questions and possible concerns.”
Injection wells, in which companies inject water produced from drilling activities deep underground, have long been connected to earthquake activity, though 99 percent of the. They narrowed it to an injection well east of the Greeley-Weld County Airport. On June 23, after a 2.6 magnitude quake in the same spot, the COGCC ordered the company to stop injections for 20 days for further study. Monitoring revealed continued seismic activity.
The COGCC stated in its release Thursday that flow rate testing on the well showed a “high permeability zone near the bottom of the well that created a preferred pathway for injected wastewater.”
In other words, water was able to slip through pathways to allow geologic structures to move.
COGCC is reviewing its injection permit standards for clarity, said Todd Hartman, spokesman for the agency.
“We continually strive to make sure that our rules are effective at ensuring that oil and gas development is done safely,” Hartman wrote in an email response to questions. “The issues with this well were highly technical in nature, and the company was cooperative in taking remedial action. Nonetheless, we are already looking at our injection permits to be sure that our expectations and requirements are clear.”
The May 31 quake was located northeast of Greeley, and it was the first that was felt by residents in many years.
Further analysis of the seismic activity in the area since the well began accepting high volumes of wastewater in August 2013 revealed a year-long pattern of seismic activity, said Anne Sheehan, a geophysics professor at CU leading the research into the well.
Based on the May 31 quake, Sheehan said her team was able to review data for the prior year to find a seismic match. The first detectable seismic activity came within months of high pressure injection starting, she said.
“There was a detectable earthquake in November of 2013, but it was not felt,” Sheehan said. “We were able to find more than a dozen prior earthquakes in the area. One was bigger than magnitude 2, and that was felt by one family close to the epicenter. There was kind of a correlation with earthquakes with that well.”
Five days ago, NGL, with approval and oversight from the COGCC, plugged 410 feet in the basement of the well, shaving it to 10,360 feet to seal off the preferential pathway and to increase the distance between the zone of injection and “basement” rock, the release stated.
“These measures are expected to mitigate the potential for future seismic events,” the release stated. Sheehan said there’s been less seismic activity since it was plugged, but it’s not totally quiet. Sheehan said she wanted to study,” Sheehan said. “For me, that was the motivation to study this very quickly, as soon as a felt earthquake happens. If you wait a long time, you could have a larger injected volume of fluid and potentially get bigger quakes. That’s partially why COGCC is being proactive, and also the injection company has done more than they’ve been asked to do. They want to get back in business, but they want to do it right.”
NGL will be allowed to resume injections today, but it will be under close monitoring by the COGCC. Sheehan and her team also will be watching.
NGL will be allowed to inject initially at a maximum rate of 5,000 barrels per day at a maximum pressure of 1,512 psi (pounds per square inch). After 20 days, the release stated, the injection rate may be increased to 7,500 barrels per day at the same pressure, the release stated.
“We are proceeding with great care, and will be tracking activities at this site closely,” said Matt Lepore, director of the COGCC, in the release. “We’re moving slowly and deliberately as we determine the right course for this location.”
Justin Rubinstein, deputy chief of the Induced Seismicity Project in Menlo Park., Calif., has been studying such manmade earthquakes, including those in Oklahoma and the recent quakes in Trinidad and New Mexico. He said the quakes all vary at so many levels, it’s hard to find a one-size-fits-all remedy.
“There’s no ready-made solution,” Rubinstein said. “It’s not something you can do with a cookie cutter” approach.
He said there are wells that are low pressure and shallow that have created induced seismicity; and there are wells on the polar opposite with high injection volumes and depths.