Active natural gas drilling in the Uinta Basin in northeast Utah, east of the town of Ouray. Drilling locations appear as bright spots, each typically 1-1/2 to 3 acres in size, connected by a network of gravel roads and pipeline corridors. Image: Flickr/John Amos
Methane is being emitted from a natural gas field in Utah at a rate of 6.2 to 11.7 percent of production, according to research accepted for publication in the journal Geophysical Research Letters.
The research adds one important data point to the ongoing question of how much methane, a greenhouse gas with a warming potential 25 times that of carbon dioxide, is emitted in the life cycle of natural gas production, transport and use. It was conducted by a team of scientists at the University of Colorado, Boulder, the Cooperative Institute for Research in Environmental Sciences (CIRES) and the National Oceanic and Atmospheric Administration's Earth System Research Laboratory.
Study co-author Colm Sweeney pointed out the discrepancy between the emissions rate his research team measured and what U.S. EPA has said it estimates as an emissions rate for the natural gas production sector.
"The important point is that we saw something that was a lot larger than these inventory methods that EPA relies on," he said.
EPA's emissions rate for the production sector is 0.88 percent. It was revised downward this year from 1.4 percent.
Sweeney said the method his team uses, flying over a basin with instruments to get a total methane emissions rate, could be used to verify the rates EPA uses.
However, the researcher was quick to caution that those concerned about leak rates from natural gas production should not try to use the numbers from the Uinta Basin, the Utah gas field where these measurements were taken, as representative of leak rates from all gas fields.
Other states have stricter rules
"There are reasons why Utah would be different from the rest of the country," he said, including the fact that a number of other states have stricter regulations on how wells are completed.
The study's findings raise many questions about which activities in the basin were leading to the high emissions rates, said Steven Hamburg, chief scientist for the Environmental Defense Fund. That group is coordinating a number of studies aimed at better quantifying emissions from natural gas, although it was not involved in this one.
"This study suggests that methane emissions may be a serious problem in Utah, but we need more data to pinpoint exactly where emissions are coming from and to identify where the opportunities are to reduce them," said Hamburg, calling this and other recent research on methane emissions "alarm bells ringing in our ears."
One of the reasons the Utah study does not pinpoint emissions sources lies in the methods used.
To calculate the methane emissions from the Uinta Basin, the scientists flew an airplane over the top of the basin and sampled the air, and then took another pass when the air mass reached the bottom of the basin. This allowed them to measure the clean air upstream and the air with added methane downstream.
While this is a good way to get total emissions of methane in a remote location where the main source of the gas is natural gas production, it is not a good way to pin emissions down to any one well, gathering or processing activity in the basin.
Sweeney said that gas companies could easily measure this themselves now that relatively cheap, portable technology exists for making such measurements (ClimateWire, Aug. 2).
'A very solvable problem'?
"We do feel this is a very solvable problem. By going to individual facilities with one of these instruments, [it is easy to] identify which ones are the big leakers and which ones are the small leakers," Sweeney said.
Another potential criticism of the study is that it only used data from one four-hour flight in February 2012. Although the researchers actually conducted 12 flights, they selected just one as their data source for this paper.