Series of earthquakes in Lawrence County linked to fracking in Utica Shale wells

Pennsylvania regulators have placed conditions and monitoring requirements on Hilcorp Energy Co.’s fracking operations in western Lawrence County to reduce the risk that its deep gas well activities could trigger more small earthquakes like the ones the company is suspected of causing last April.

The conditions were put in place after the state Department of Environmental Protection concluded that fracking in two of the Texas company’s wells showed a “marked” link in space and time to a series of minor tremors in Lawrence County on April 25.

DEP released its findings Friday, but the company has been implementing the state’s recommended practices since at least November.

The requirements so far apply only to the company’s operations in three townships, but DEP officials said that they intend to write a regulation that will apply to all companies in specific areas of the state where Utica Shale operations might be susceptible to seismic risks because of proximity to faults or brittle basement rock.

Acting DEP Secretary Patrick McDonnell said an important part of the agency’s review of the Lawrence County seismic events was “to formulate procedures to reduce seismic risk going forward.”

The Lawrence County earthquakes are the first known incidents of fracking-linked quakes in Pennsylvania.

PG graphic: Earthquake mapping
(Click image for larger version)

Researchers have linked fracking to earthquakes in several sites in Ohio, Oklahoma, England and Canada, but cases of recorded or felt earthquakes directly tied to fracking are rare and the science on so-called induced earthquakes is evolving.

At the time of the quakes, Hilcorp was fracking two of four Utica wells on its North Beaver NC Development pad using a technique called “zipper fracking,” in which two parallel wellbores spaced close together are injected with high-pressure fluids simultaneously to extract more gas from the shale, according to DEP’s report.

Seismic networks measured shaking that ranged in magnitude from 1.8 to 2.3 in Mahoning, North Beaver and Union. People generally do not feel earthquakes smaller than magnitude 3.

Elevated pressures associated with zipper fracking could exacerbate seismic risks in some situations, DEP officials said.

Hilcorp voluntarily stopped its activities at the well pad on April 25 and later reported that it would discontinue fracking operations at the site indefinitely.

In a statement, Hilcorp spokesman Justin Furnace said the company is reviewing DEP’s report. “We will continue to work with DEP to implement the plan outlined in the report,” he said.

DEP said that while it has not yet established a “definitive geologic association” between the fracking and the earthquakes, the correlation in space and time is enough to institute new requirements on Hilcorp’s activities in the three townships.

Those steps call for Hilcorp to continue operating its own seismic monitoring network in the area and to stop using zipper fracking on wells closer than a quarter-mile apart.

DEP also is requiring the company to notify regulators when it senses seismic events of magnitude 1 or greater within 6 miles of its wellbore; to temporarily suspend and modify its fracking operations when it senses a series of three events between magnitude 1.5 and 1.9; and to shut down its fracking operations when it senses a quake of magnitude 2 or greater within 3 miles of its wellbore. Fracking operations would be allowed to resume if DEP determines that it can be done safely.

DEP is recommending that other operators in the area follow similar plans. Agency officials also said they will continue to monitor for small quakes that seem linked to human causes that are picked up by the state’s recently improved seismic monitoring network, which provides nearly realtime data. The network detects magnitude 2 quakes anywhere in the state and lower-magnitude events when they happen close to the network’s 41 sensors.

The Lawrence County earthquakes share characteristics with a series of induced earthquakes in Poland Township, Ohio, in 2014 that occurred roughly one to eight miles from the epicenters of the Pennsylvania quakes, DEP's report said.

Both were linked to fracking at Hilcorp’s Utica wells and both triggered seismic activity at depths between the Utica Shale and the crystalline basement rock.

At the Pennsylvania site, the wells were targeting the Utica Shale 7,900 feet below the surface and the basement rock in the area was about 2,000 feet below it.

But while researchers discovered that the Ohio quakes occurred along a fault near the top of the basement rock, regulators and other reviewers have not been able to identify a fault in the area near the Pennsylvania quakes. DEP acknowledged that the quality of the fault mapping in the area is limited.

“If there is a tectonic earthquake, there has to be a fault there, by definition,” said Ray Beiersdorfer, a geology professor at Youngstown State University. He said he was disappointed that DEP has not identified where and what type of fault it is.

Laura Legere:

First Published February 17, 2017 10:25 AM

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