Methane leaks from three large US natural gas fields in line with federal estimates

"We are beginning to get a sense of regional variation in methane emissions from natural gas production," said lead author Jeff Peischl, a scientist with the Cooperative Institute for Research in Environmental Sciences (CIRES) in Boulder, Colorado. "The gas fields we studied for this paper produced about 20 percent of the natural gas in the United States, and more than half the shale gas, so this moves us closer to understanding methane leaks from U.S. natural gas production."

Peischl's team's analysis appears online today in the Journal of Geophysical Research: Atmospheres, published by the American Geophysical Union.

In the new paper, Pieschl and his colleagues used sophisticated measurements taken from a research aircraft of the National Oceanic and Atmospheric Administration (NOAA) to determine methane emissions from the Haynesville, Fayetteville, and Marcellus regions during five flights in the summer of 2013. CIRES is a partnership of NOAA and the University of Colorado Boulder.

Overall, the team found that methane leaking from gas equipment totaled about 1.1 percent of gas produced in those regions; estimates from the Environmental Protection Agency, based on average equipment leak rates, put that figure at about 1 percent.

"It is good news that our atmospheric measurements are close to the EPA estimates," said co-author Joost de Gouw, a CIRES scientist who also works at NOAA. "If leak rates are too high, natural gas does not compare favorably with one alternative, coal, in terms of climate impact. Where leak rates are low, the comparison favors natural gas."

In the new study, the researchers also reported their findings by region:

• Methane emissions in the Marcellus region of northeastern Pennsylvania were about 16.5 tons (33,000 lbs) per hour, or 0.18-0.41 percent of production.
• Methane emissions in the Haynesville shale of eastern Texas/northwestern Louisiana of about 88 tons (176,000 lbs) per hour, or 1.0-2.1 percent of production.
• Methane emissions in the Fayetteville shale region of Arkansas were roughly 43 tons (86,000 lbs) per hour, or 1.0-2.8 percent of produced gas.

In other published papers, CIRES, NOAA and other researchers have found methane losses of:

• About 4 percent of natural gas production in the Denver-Julesberg Basin
• 6-12 percent of natural gas production in Utah's Uinta Basin (also called Uintah)
• About 17 percent of natural gas production in the Los Angeles Basin

The Colorado, Utah and California basins combined produce less than 3 percent of all U.S. natural gas, much less than the eastern basins.

The variable methane leak rates in the different studies suggests that other chemicals emitted during gas production, including compounds that contribute to episodes of poor air quality, are also variable, de Gouw said. There could be many reasons for significant regional differences in leak rates, he added. The composition of gas can vary across different regions, with slightly more or less methane, for example. And equipment, techniques and regulations vary, as well.

The CIRES and NOAA team is planning another aircraft mission this spring, to expand emissions measurements from gas-producing regions stretching from Texas to North Dakota. The researchers hope that, taken together, the studies will help industry identify the conditions and techniques that minimize the leaks during gas production, benefiting both the atmosphere and the industry's bottom line.