Preventing human-caused, fracking-related earthquakes
She requested seismometers from a consortium that rapidly supplies equipment for earthquake aftershock monitoring. She began talking with her graduate students, colleagues from the USGS and the oil and gas industry, and regulators about where to deploy the equipment.
The first week of June, Yeck and fellow graduate students Jenny Nakai and Matthew Weingarten deployed six seismometers in an array around the earthquake’s epicenter to monitor further seismic activity. As data flowed in, they analyzed it in detail to pinpoint the locations and the timing of smaller earthquakes following that first one.
The geophysicists communicated their findings with state oil and gas regulators and wastewater disposal company staff, and helped those staff learn to read and understand real-time seismic data themselves.
It quickly became clear that the earthquakes were centered under one specific well: the wastewater disposal well closest to the Greeley earthquake epicenter which happened to be the highest‐rate injection well in northeast Colorado in 2013, according to data compiled by the state. The well had been pumping an average of 250,000 barrels per month since August 2013, more than a mile deep.
“Soon after the magnitude 3.2 earthquake, when the seismic network was in place, we shared earthquake locations and earthquake magnitude frequency with the Colorado Oil and Gas Conservation Commission and local energy companies to better inform them of seismic activity occurring around the wells,” said Jenny Nakai, a co-author of the new study and a graduate student in geophysics at CU Boulder. “We could see fluctuations in seismic activity as the well was shut down and cemented.”
Injection stopped on 24 June for a month, and the company that drilled the disposal well took two actions to reduce seismicity: They reduced injection rates and used cement to plug the bottom of the well, impeding fluid interaction with deeper, subsurface faults.
Injection resumed a month later at reduced rates, starting at just 5,000 barrels a day mid-July. The injection rates were slowly increased over time.
Seismicity dropped, the team found. Following mitigation, between 13 August 2014 and 29 December 2015, no earthquakes larger than magnitude 1.5 occurred near Greeley.
USGS notes that the research team also used data from more distant seismometers, deployed well before the 2014 earthquake, to detect past seismic activity in the area. They found the Greeley earthquake sequence began roughly four months after the initiation of high-rate wastewater injection in 2013. Their analysis suggested that the biggest observed earthquakes in the area were getting bigger over time, an observation made at other injection induced earthquake locations as well.
State regulators with the Colorado Oil and Gas Conservation Commission modified requirements as a result of the seismology team’s findings, Yeck and his colleagues reported in the paper. Regulators began requiring seismic monitoring at recently permitted commercial disposal wells pumping more than 10,000 barrels per day.
Greeley-area seismicity continues to be monitored both by the CU Boulder team and by an independent contractor.
— Read more in William Yeck et al., “Rapid Response, Monitoring, and Mitigation of Induced Seismicity near Greeley, Colorado,” Seismological Research Letters 87, no. 4 (July 2016) (DOI: 10.1785/0220150275)
