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Study: small fraction of Pa. wells contribute large portion of methane emissions

Researchers used the Purdue Airborne Laboratory for Atmospheric Research, a specially equipped airplane, to measure plumes of methane gas above shale gas wells in southwestern Pennsylvania.

Photo courtesy of Paul Shepson

Researchers used the Purdue Airborne Laboratory for Atmospheric Research, a specially equipped airplane, to measure plumes of methane gas above shale gas wells in southwestern Pennsylvania.

In a new study on methane emissions from natural gas development, researchers found that a significant portion of the emissions they measured came from just a small fraction of Marcellus Shale wells. Those wells were in the drilling phase and had not yet been hydraulically fractured to release natural gas.

The study, published Monday in the Proceedings of the Natural Academy of Sciences, comes as the Obama administration pursues a plan to curb methane emissions that contribute to climate change. On Tuesday, the EPA released five white papers on emissions of methane and volatile organic compounds in the oil and gas sector.

Scientists from Purdue and Cornell Universities gathered emissions data using a special research plane that flew above natural gas well sites in southwest Pennsylvania and West Virginia. They found that seven well pads, representing about 1 percent of all the wells in the research area, accounted for 4 to 30 percent of the emissions they recorded.

EnergyWire reports the study challenges the federal Environmental Protection Agency’s estimates that show emissions during the drilling phase are much lower.

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The scientists cataloged emissions over parts of Greene, Washington and Fayette counties in Pennsylvania and Marshall and Ohio counties in West Virginia. They soon homed in on a region between Washington County and the border of West Virginia that seemed to be emitting particularly high amounts of methane.

They flew into the wind to identify the source of the plumes and quantified the rate at which gas was escaping.

The 40 wells were together emitting 34 grams of methane per second per well. That is two to three orders of magnitude higher than the amount estimated by the EPA emissions inventory for drilling.

“It is particularly noteworthy that large emissions were measured for wells in the drilling phase, in some cases 100 to 1,000 times greater than the inventory estimates,” said Purdue professor Paul Shepson, a co-author of the study.

This study is the latest attempt by scientists to understand sources of methane emissions from oil and gas development. A Stanford study published in February found federal estimates significantly undercount the amount of methane emitted in the U.S. That study also noted that a small number of “super-emitters” could be responsible for a significant amount of the leakage from natural gas systems.

Methane is a more potent, but shorter-lived greenhouse gas than carbon dioxide. Burning natural gas instead of coal at large power plants has helped lower energy-related carbon emissions in the U.S., but methane leaks could dampen those climate benefits.

A spokesman for the Marcellus Shale Coalition said in an e-mail that the trade group is still reviewing the study, but that the EPA’s annual greenhouse gas inventory, released on Tuesday afternoon, “reaffirms the fact that shale gas production is soaring and emissions continue to drop, especially here across the Appalachian Basin, where strong regulations are in place and operators are deeply committed to enhancing air quality through leveraging industry-leading technologies.”

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