Two studies led by researchers at Colorado State University found that emissions of methane – a potent greenhouse gas – vary widely, and that leaks from just a few sources dominate the overall amount of emissions.
In one study, the scientists measured methane emissions from natural gas gathering and processing facilities. They looked at 114 gathering and 16 processing facilities, and found 30 percent of the facilities were responsible for 80 percent of the leaks.
The other study analyzed emissions from compressor stations, and found a similar pattern.
"Essentially what this means is a very small fraction of the facilities are producing a majority of the emissions," said Allen Robinson, a professor at Carnegie Mellon University and a co-author of both studies.
"These few very high emitting facilities are very often referred to as super-emitters."
The researchers took measurements at gathering and processing facilities across the United States, from the Denver-Julesburg basin in Colorado to the Appalachian Basin in the Northeast.
Gathering facilities take natural gas from a web of wells en route to a larger pipeline, compressing and dehydrating the gas along the way. Such facilities often take gas to larger processing operations, which separate out other gas products like propane and butane.
The second study, which looked at leaks from compressor stations, which are part of the natural gas transportation network, found that just two out of the 45 facilities it analyzed – from across the United States – had extremely high leaks of methane.
"These few very high emitting facilities are very often referred to as super-emitters," said Robinson. Often the leaks came from facilities that had something wrong with them, "a broken valve, something like that," he added.
The studies were part of a multiyear research effort led by the nonprofit Environmental Defense Fund. The environmental group has organized a series of studies aimed at quantifying how much methane leaks from natural gas production, processing, transportation and use.
If leaks can be kept to a low level, natural gas is a more climate-friendly fuel than coal. However, with higher leak levels, it becomes less beneficial from that perspective.
The data collected for both studies is far more comprehensive than any other data set on leaks from such facilities, the researchers said. The results show that the Environmental Protection Agency figures for emissions from these sectors may be missing a large number of methane leaks.
"Only about one-third of those emissions would be reported to that [EPA] new reporting program. And so there are a lot of gaps that would not be reported," said Anthony Marchese, a CSU professor of mechanical engineering who led the study.
Colorado is leading the way in cracking down on methane emissions from oil and gas. It released new regulations in February 2014 that many see as a model for other oil and gas producing states wishing to curb methane emissions.
Marchese said the measurements for the gathering and processing study were completed before Colorado's rules went into effect. He believes the state's regulations should cut down on emissions.
"I think you will see some effect of that in the future," he said.
