Geophysicist investigating Greeley quake's cause
GREELEY – A geophysicist from the University of Colorado is hoping to settle the question of whether a small earthquake last weekend near Greeley was caused by wastewater injection wells.
The Greeley Tribune reported Friday that Anne Sheehan and a team of graduate students have been deploying seismographs to study the magnitude 3.4 quake. The U.S. Geological Survey determined the epicenter of the quake was believed to be 5 miles beneath the surface about 4 miles northeast of Greeley.
The suspected epicenter is near two injection wells. The May 31 earthquake caused no damage.
"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.
Weld County has 28 injection wells for oil and gas waste, or "Class II" disposal wells.
State drilling regulators said earlier this week they were skeptical that the wells caused the earthquake.
The epicenter is difficult to determine, said Justin Rubinstein, a seismologist in Menlo Park, California, who has studied the increasing phenomenon of man-induced earthquakes for the past 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."
The injection wells in question were those of High Sierra Water Services, which manages injection wells throughout Weld County.
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.