MORGANTOWN, W.Va. (AP) — Human activity associated with oil and gas production can sometimes cause earthquakes, but the problem is not hydraulic fracturing, a seismologist from the University of Texas told researchers gathered for a two-day conference on Marcellus shale-gas drilling.
When the rare quakes do occur, they’re typically linked to the disposal of drilling fluids in underground injection wells, Cliff Frohlich said Monday at West Virginia University. And the vast majority of injection wells don’t cause quakes, either, he said.
Frohlich cited six earthquakes since 2008 in Texas, Arkansas, Colorado, Ohio and Oklahoma, ranging from magnitude 3.3 to magnitude 5.7. Their locations show that human-caused earthquakes are geographically widespread and geologically diverse, but “very rare,” given the amount of petroleum produced and the amount of waste being disposed of.
Why some injection wells cause earthquakes and others don’t remains unclear, he said. Frohlich hypothesizes that quakes occur when a “suitably oriented” fault lies near an injection site.
“Hydraulic fracturing almost never causes true earthquakes,” he told the group gathered for the National Research Council workshop. “It is the disposal of fluids that is a concern.”