MORGANTOWN, W.Va. -- 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 Arkansas, Colorado, Ohio, Oklahoma and Texas, 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."
Texas has 10,000 injection wells, Frohlich said, and some have been in use since the 1930s. That effectively makes the state a giant research lab for the shale-gas drilling issues now facing Appalachian states including New York, Ohio, Pennsylvania and West Virginia.
If injection wells were "hugely dangerous," he said, "we would know."
"Texas would be famous as a state that just rocks with major earthquakes," Frohlich said. "That is not true."
WVU Vice President for Research Fred King said reports the workshop will generate should be available before the start of West Virginia's legislative session in January and could help guide future regulatory discussions.
Frohlich urged policymakers to consider cultural and population differences if they are weighing regulation aimed at minimizing the risk of earthquakes through either the spacing between or monitoring of injection wells.