Ohio officials said Tuesday that an oil and gas well near the site of two small earthquakes was undergoing hydraulic fracturing, or fracking, when the quakes occurred.
The State Department of Natural Resources ordered work halted at the well and six others in Poland Township, near the Pennsylvania border, on Monday after the two earthquakes earlier in the day. The quakes, of magnitude 2.6 and 3.0, caused no damage or injuries but were felt in nearby towns.
The department said it acted “out of an abundance of caution” to suspend the operation by Hilcorp Energy, a large independent oil and gas producer based in Houston. It is the only such operator in the area, which is about 15 miles southeast of Youngstown.
Mark Bruce, a spokesman for the department, said it was too early to determine whether drilling operations induced the earthquakes. “What we’re focusing on now is getting all the data from the company,” he said. “We’ll examine it first and decide next steps after that.”
But Mr. Bruce said one of the affected wells had been undergoing fracking to release oil and gas. In fracking, large amounts of water, sand and chemicals are pumped into a well to break up the rock — in this case, a formation known as the Utica shale — to free hydrocarbons.
Over the past decade, shale oil and gas production has been linked to earthquakes in Ohio, Arkansas, Oklahoma and other states, and in several countries. In most cases, however, the quakes were tied to disposal wells, in which wastewater from oil and gas production is injected under pressure into permeable rock formations. The water is thought to alter pressures underground and unclamp old faults, allowing them to slip.
There have been only a few instances — in British Columbia, England and south-central Oklahoma — in which the fracking itself was thought to have induced quakes large enough to be felt.
Mr. Bruce said there were no disposal wells in the area where the quakes occurred Monday.
A disposal well in Youngstown was permanently shut in 2012 after it was linked to a series of quakes that began there three years ago, and no new disposal wells have been allowed within five miles of the site.
Hilcorp Energy said it was cooperating with the state investigation. “We are not aware of any evidence to connect our operations to these events,” the company said in a statement, pointing out that other wells had been drilled in the Utica shale in Ohio in recent years without a problem.
A spokesman for the company said drilling of the wells in Poland Township, at an old landfill, had begun in 2012. The wells were in various stages of completion, he said, and only one was producing oil and gas. They were drilled to a depth of about 1.5 miles and then extended horizontally for about a mile through the shale.
That depth is the same recorded for the first quake Monday by the United States Geological Survey, although depth measurements for earthquakes are often only approximate. The first quake, of magnitude 3.0, occurred around 2:30 a.m., followed by the 2.6-magnitude quake nine hours later. Preliminary analysis showed they were centered within several thousand feet of the wells. The smaller quake was estimated to have originated about three miles underground.
During the series of quakes in Youngstown in 2011 and 2012, state officials called in geoscientists to analyze the quake data and study the geology of the area.
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