A series of earthquakes recorded late last month in western Pennsylvania could be linked to a Hilcorp Energy Co. site where the company was stimulating two horizontal wells near the epicenter, state researchers said this week.
"We have not done enough analysis of the data to make any conclusions yet," said Pennsylvania State University Professor of Geosciences Andrew Nyblade, who also helps lead the state's seismic monitoring network. "But there is a correlation spatially and temporally between the fracking and the earthquakes."
The state's monitoring network detected five micro-earthquakes, which could not be felt by people, on April 25 and 26 in Lawrence County's Mahoning Township that ranged in size from 1.7- to 1.9-magnitude (see Shale Daily, April 27). The epicenter in Mahoning -- about 60 miles northwest of Pittsburgh -- was near Hilcorp's four-well pad operated by subsidiary North Beaver NC Development.
The company voluntarily idled its operations at the site the day the earthquakes were detected. It ceased fracking and shut-in two producing wells there. The pad was offline for more than a week after the incident (see Shale Daily, May 4).
Pennsylvania Department of Environmental Protection (DEP) spokesperson Melanie Williams said Thursday that operations at the pad have since resumed. Two of the wells are now producing and the other two are on flow back.
She added that state regulators are regularly meeting with Hilcorp officials to review data.
“The investigation is ongoing and will not end until definitive conclusions can be drawn about the incident,” she said. “It is not known at this time when that will be. DEP will issue a report detailing the conclusions of the investigation.”
Hilcorp had fractured two of the wells on the pad on March 30, and they were completed before the earthquakes. The company has not commented about the incident. But DEP said the company was stimulating the other two wells at the time some of the earthquakes were recorded.
In September, DEP and DCNR announced that they would contribute about $531,000 to expand and maintain a real-time network of 30 seismic monitoring stations in conjunction with Penn State, which had already been monitoring activity for years (see Shale Daily, Sept. 29, 2015).
Penn State said this week that the network is almost complete, with the last of the work slated to be finished this summer.
"This network has greatly improved our capability to detect seismic events too small to be felt by people on the ground," said DCNR state geologist Gale Blackmer. "The data is an important research tool to better understand the state's geology, and it provides an improved picture of naturally occurring seismic events, as well as induced events that might result from quarry blasts, [injection], and hydraulic fracturing."
The network was designed with a detection threshold of a 2.0 magnitude, but the Lawrence County earthquakes revealed that it could be more sensitive, Penn State said.
The state has relatively low levels of natural earthquake activity, but small tremors do occur there. No seismic activity has ever officially been linked to underground injection or fracturing in the state. The Mahoning well pad site is about six miles east of another Hilcorp pad in Ohio that state regulators linked to a series of earthquakes there in 2014 (see Shale Daily, April 11, 2014).
Penn State said once the seismic monitoring network is finished, data from the stations will be uploaded to a website that can be accessed by the public.