April 20 (UPI) -- A small tremor was recorded early Friday in the shale heartland of Oklahoma, one day after state regulators limited work because of seismic activity.
The U.S. Geological Survey recorded a magnitude-2.8 tremor at 2:32 a.m. EDT near the town of Hennessey, Okla. That followed a magnitude-3.2 tremor in the same area Thursday morning and is part of a large cluster of seismic activity in the region over the last 30 days.
The state Oil and Gas Conservation Division on Thursday ordered Choate Disposal Services LLC to stop operations at one of its wells near the Arbuckle formation.
One of the U.S. states with a significant amount of shale oil and natural gas, a study from the USGS found the disposal of oil and gas-related wastewater is the "primary reason" for an increase in seismic activity in central states like Oklahoma. That process is different from hydraulic fracturing.
The state, however, said that seismic activity outside the main area of activity in central Oklahoma has been tied to hydraulic fracturing, though those events account for less than 4 percent of state activity.
The directive from the conservation division called on Choate to reduce disposal volumes by 25 percent to an area within 10 miles of the Thursday tremor near Hennessey.
"Researchers are in broad agreement that disposal into the Arbuckle formation in Oklahoma poses the largest potential risk for induced seismicity," the division's order to Choate read.
In its annual strategic plan, the state agency said it was still coping with the lingering challenge of addressing seismic activity by limiting the injection of water into disposal wells. Funding for the effort last year came from a one-time grant, but lawmakers denied a funding request for the effort in fiscal year 2018.
It's an election year in 2018 for Oklahoma and a term limit for Gov. Mary Fallin means a crowded field of candidates who could inherit a looming budget crisis for the shale-rich state. The state accounts for about 5 percent of total U.S. oil production.