WASHINGTON — Researchers found higher-than-expected emissions of a potent greenhouse gas emanating from Pennsylvania wells, according to a study published Monday that adds to concerns about the environmental footprint of natural gas.
The study, conducted by Purdue and Cornell universities and published in the Proceedings of the National Academy of Sciences, is the latest to scrutinize methane emissions associated with natural gas development, with implications from New York to Texas.
Researchers used a specially equipped airplane to collect samples above the Marcellus Shale in southwestern Pennsylvania. They traced large methane emissions to seven wells that were were being drilled, a phase of operations not normally associated with such high levels. That suggests the U.S. Environmental Protection Agency’s estimates, released in an annual inventory, are not capturing all the released methane.
Some of the methane may have been unlocked as drill bits pass through underground coal seams common in the area.
“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 chemistry professor Paul Shepson. “This indicates that there are processes occurring — such as emissions from coal seams during the drilling process — that are not captured in the inventory development process.”
The seven high-emitting sites represented just 1 percent of the total number of wells, but were the sites of 4 percent to 30 percent of the emissions in the area.
“This is another example pointing to the idea that a large fraction of the total emissions is coming from a small fraction of shale gas production components that are in an anomalous condition,” Shepson said.
Methane, the main component of natural gas, is 28 times to 34 times more potent than carbon dioxide over 100 years, even though it dissipates much more quickly in the atmosphere.
Although methane has declined 11 percent since 1990, some expect it to start climbing again as a result of the domestic oil and gas drilling boom. And significant methane emissions could undermine the climate change benefits of generating more electricity from natural gas, which produces about half as much carbon dioxide as coal.
Critics say the EPA does an inadequate job tracking all of the greenhouse gas emissions associated with surging domestic energy development tied to horizontal drilling and the hydraulic fracturing technique of pumping water, sand and chemicals underground.
The government’s greenhouse gas emissions inventory generally relies on discrete measurements — often taken by industry at the ground level — which then are extrapolated and applied more broadly. The Purdue-Cornell study suggests that ground-level data could miss some methane that is detected by planes and other monitors higher up.
Related story: White House plan to cut methane takes aim at oil industry
Separate research on the horizon could help explain discrepancies between top-down aerial monitoring and bottom-up, ground-based data.The EDF is coordinating 16 studies examining methane releases associated with natural gas from the wellhead to the end user, with four using aerial measurements and two using data from sensors on buildings.
The growing body of research surrounding methane releases from natural gas activities is providing “greater clarity,” said Steven Hamburg, EDF’s chief scientist. “But we’re not all the way there yet.”
“We have to look at how individual observations fit into the bigger picture,” Hamburg added.
Katie Brown, a spokeswoman for the industry group Energy In Depth, noted that two of the researchers involved in the new study, Cornell ecologist Robert Howarth and engineering professor Anthony Ingraffea, have been critical of natural gas previously. Howarth was the lead researcher behind a 2011 study on methane leaks widely cited by gas industry foes.
“Ingraffea and Howarth are activists who want to ban hydraulic fracturing, so it’s not surprising that they arrived at a conclusion to advance the cause,” Brown said.
“Direct measurements have shown that methane emissions are far below what alarmists have claimed,” Brown added. “You have to give credit to these guys for their persistence and inventive ways of making their argument, but the science hasn’t changed.”
Energy companies have already taken some steps to to plug methane leaks at oil and gas wells.
Under EPA mandates that go into effect next year, companies will have to use “green completion” equipment to capture pollution from natural gas wells during the flowback stage of operations, when gas and fracturing fluids surge out of the ground.
A University of Texas study published last year suggested that the green completions rule already is making a major dent in methane emissions from natural gas wells, as energy companies adopt the required technology ahead of next year’s deadline.
The Obama administration is poised to go further, with a new Interior Department rule cracking down on emissions from wells on public land and possibly new EPA regulations on the horizon. Under a broad blueprint unveiled by the White House in March, the EPA will decide this fall whether to impose new rules aimed at further paring methane emissions from storing, transporting and processing oil and natural gas.
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