From The Greeley Tribune (Sharon Dunn):
A small team of Boulder graduate students and their professor hope to soon put an end to the mystery of what created a small magnitude earthquake on Saturday northeast of Greeley.
While the quake measured 3.4 in magnitude — barely enough to be felt and not enough to cause damage to structures — the coincidence of its proximity to wastewater injection wells has researchers pondering the potential of an oil and gas role.
Yes, it could be natural, scientists say. It’s not altogether impossible the Greeley area could have a natural earthquake — though there hasn’t been any such activity in a good 30 years.
A temblor of that size could happen anywhere in the country, seismologists say.
But recent years have proven throughout drilling fields in Ohio, Oklahoma and Texas that the connection between quakes and oil and gas wastewater disposal wells is rather strong.
That’s where University of Colorado at Boulder geophysics professor Anne Sheehan and her small team of graduate students come in. They spent the last several days deploying seismographs in and around what the U.S. Geological Survey determined was the epicenter of the quake believed to have originated five miles beneath the surface about four miles northeast of Greeley.
They “believe” only because the closest station to record tectonic activity is in Idaho Springs, 70 miles away.
The epicenter of the quake was a bit of an educated guess, as well as the depth. But based on what are called “felt reports,” in which area residents reported what they felt at the time of the earthquake, Sheehan has been able to zero in a little better on the area to get the best readings.
Having seismographs closer in the suspected area — which is near two injection wells — will help scientists get a better fix on the cause.
“I guess we wouldn’t have done this if we didn’t think there would be some small follow-up earthquakes,” Sheehan said. “It’s possible we won’t record anything of interest. One would hope there would not be any more earthquakes. But if there are, we will study them.”
In fact, just two hours after Saturday’s quake, there were three smaller tremors that followed, Sheehan said. One was 2.0 and the other two were 1.4 in magnitude. Those aren’t recorded at the USGS in Golden, which only tracks quakes of 2.5 magnitude and above.
Wastewater disposal wells take in produced water from fracking and drilling operations, a practice that has been going on for several years and which is practiced by a variety of industries.
There are about 150,000 injection wells across the country — 40,000 of which are for oil and gas waste, or “Class II” disposal wells. Weld County has 28 of them.
There were two injection wells in proximity to the epicenter of Saturday’s quake, one dug more than 8,700 feet deep and the other 10,700 feet. One is 20 years old, the other just two years old.
Colorado Oil and Gas Conservation Commission officials earlier this week said they were skeptical that the wells caused the quake because they believe the three historic well-related quake instances recorded in Colorado all shared one common characteristic: the point of injection was the epicenter of the quake.
They said that wasn’t the case in Greeley.
But even that is difficult to measure, given the inexact measuring from 70 miles way, said Justin Rubinstein, a seismologist in Menlo Park, Calif., who has studied the increasing phenomenon of man-induced earthquakes for the last three years.
“As long as there is a pathway for the fluids to transfer, it doesn’t matter where you’re injecting,” Rubinstein said of the misconception on locations. “Faults are an incredible transmitter of fluids and fluid pressures. Just because earthquakes are occurring deeper than where injections are, there’s no reason to say they can’t be related.”
But, he said, there’s little proof of any cause at present, and he wouldn’t rule out a natural quake.
An injection well is dug 10,000 feet below the surface into very porous rock. The rate and volume of the water that is pumped in is governed by state and federal regulations.
Once pumped into the porous rock, the water disperses through that formation, allowing more water to be pumped in.
Sometimes the pressure of the water is such that it causes earthquakes in the existing faults.
The injection wells in question were those of High Sierra Water Services, which manages injections wells throughout Weld County and also recycles produced water for companies.
High Sierra also recycles produced water in an ever-growing amount, shipping it back out to the field for further use in drilling.
“We looked at our charts and we’re operating within the parameters of the well and it’s been operational for quite some time,” said Josh Patterson, operations manager for the company.
Sheehan said by studying whether any subsequent quakes are a result of injection wells potentially being drilled into faults, or the wrong rocks, or were simply overvalued in terms of volume and rate capacities, will help bring about better practices in the field.
“If we find out something useful about whether injection causes earthquakes, it might be something that the industry can use to do a better job of injecting, if that turns out to be a problem,” Sheehan said. “So maybe if they inject at lower volumes or spread it out more, it could be that there are things that we’ll learn that can help inform some sort of best practices.”
More oil and gas coverage here.