Critics of the natural gas extraction technique known as fracking have long criticized it for leaking too much methane — a potent greenhouse gas — into the atmosphere during the extraction process. The Environmental Protection Agency recently estimated that natural gas operations emitted about 145 million metric tons of methane in 2011, making it the biggest source of these emissions in the country.

Now a new study, sponsored by the Environmental Defense Fund (EDF) and nine energy petroleum companies, finds that emissions may be lower than previously thought, at least during part of the extraction process. According to the study (pdf), published in the Proceedings of the National Academy of Sciences, the average methane emissions from the well completion flowbacks at 190 natural gas sites ranged from 0.01 metric tons to 17 metric tons. The EPA's estimate worked out to 81 metric tons per site. The study also found that leaks in other parts of the process — pneumatic pumps, controllers and other equipment — was either equal to or higher than the EPA previously estimated. Ultimately, this meant that total emissions came pretty close to the EPA's estimates.

The researchers, from the University of Texas, came up with these numbers by taking direct measurements of methane emissions. Previous calculations were less direct and used either engineering estimates or airplane flyover measurements.

One of the study's co-authors told Inside Climate News that he hopes this information will help to "call attention to best practices" in the industry which can reduce methane leaks.

The $2.3 million study has earned criticism over its funding, 90 percent of which came from petroleum companies. Critics also point out that the natural gas industry chose the sites, so the results of the study may not be indicative of the average natural gas well. According to a press release (pdf) from the EDF, the majority of the wells tested had "equipment in place that reduces methane emissions by 99 percent." There is no indication of how universally that technology is applied throughout the industry.

But the fact that the technology appears to work can be considered good news. The study "shows that when producers use practices to capture or control emissions ... methane can be dramatically reduced," EDF Associate Vice President Mark Brownstein said in the press release. "The study also demonstrated, however, that certain methane emissions are larger than previously thought, indicating that there are many further opportunities to reduce emissions."

In addition to the EDF, funders for this new study include Andarko Petroleum Company, BG Group, Chevron, Encana Oil & Gas, Pioneer Natural Resources Company, Shell, Southwestern Energy, Talisman Energy, and ExxonMobile subsidiary XTO Energy.

Related on MNN: