The Colorado Oil and Gas Conservation Commission ordered NGL Water Solutions to stop dumping water into the well late last month, after two significant quakes in the Greeley area -- the first of any significance to strike the town in forty years -- occurred three weeks apart. (The larger of the two, a 3.4-magnitude temblor, was felt as far away as Golden and Boulder.) But COGCC lifted the ban in mid-July, after imposing new restrictions on the volume of water NGL is allowed to inject into the well on a daily basis.The new limits were imposed after studying data from six seismometers placed around the site. The machines detected close to 500 quakes between June 3 and July 21, and location data from sixty of those events leaves little doubt that the NGL operation is at the center of the seismic activity, says Anne Sheehan, a geophysics professor at the University of Colorado Boulder.
Sheehan says the quakes were "really small" -- most of them of zero magnitude or less on the logarithmic Richter scale -- and appear to have tapered off over time. "We're watching closely and communicating with [COGCC] to make sure it's not ramping back up," she adds. "So far, it's been pretty quiet."
NGL was pumping up to 300,000 barrels a month of water extracted from fracking wells into the injection well. COGCC allowed the company to resume operations at half that level, reducing the volume of fluid from 10,000 to 5,000 barrels a day. But after twenty days, if the area remains absent of unusual seismic activity, the maximum injection rate can be increased to 7,500 barrels a day.
The decision to allow the operation to resume has been harshly criticized by antifracking activists. "They are resuming injection of toxic fracking waste under Greeley even though they think it's connected to the earthquakes," complains Gary Wockner, a Fort Collins-based environmental writer. "This is consistent with the industry's business model to frack first, grab all the money, and leave the problems for taxpayers and homeowners to clean up."
But Sheehan says NGL's well, which is nearly 11,000 feet deep, is not a typical injection well: "There are a lot of wells that don't have earthquakes. This one was drilled very deep and has had high rate of volume -- 300,000 barrels a month is high for Colorado. And the bottom of the well was highly permeable and fractured."
With COGCC's okay, NGL has sealed off the bottom of the well, increasing the distance between the area of high-pressure injection and so-called "basement" rock. "I was surprised they decided to do that," Sheehan says. "Cementing that is not cheap. Hopefully, it will make the well safer."
State officials say they will continue to monitor the well closely, even as more data is developing from other studies about the relationship between fracking wastewater disposal and earthquakes. As noted three weeks ago in our cover story on Colorado's central role in the country's current energy wars, recent studies by U.S. Geological Survey researchers have tied Oklahoma's 2011 5.4-magnitude shocker, the biggest quake in the state's history, to injection wells, and indicated that a series of small, human-induced quakes could trigger a "cascade of earthquakes" of greater intensity. Have a tip? Send it to email@example.com.