WASHINGTON -- Natural gas leaks from production wells are lower than previous estimates and below the level that would erase the fuel's climate benefit over coal, according to a University of Texas study released Monday and backed by both industry and environmentalists.
The study, the first to use actual measurements of emissions, found that 0.42 percent of natural gas produced in the U.S. is released into the atmosphere. A 2010 Cornell University study using data provided by drillers estimated leakage at 0.6 to 3.2 percent.
"The question was, as we bring more natural gas on board, what are the methane emissions, and are they so high that we're creating a problem for the climate," said Steven Hamburg, chief scientist at the Environmental Defense Fund. "No process is going to be 100 percent tight, and so the question is how low can we get it."
When it's burned to produce electricity, natural gas emits about half the carbon dioxide, the main greenhouse gas, as coal. If too much methane escapes, the environmental benefit is lost.
Methane, the main component of natural gas, is 21 times more potent at trapping heat in the atmosphere than carbon dioxide, according to the Environmental Protection Agency. A boom in U.S. natural gas supplies brought on by hydraulic fracturing has opened a debate over whether expanding the use of gas sets back efforts to fight climate change.
The University of Texas worked with the Environmental Defense Fund and nine gas producers, including Houston-based Southwestern Energy Co., on the report. Over the course of a year, researchers took direct measurements at 190 well sites in the Gulf Coast, Great Plains, Rocky Mountain and Appalachian regions.
Wenonah Hauter, executive director of Food & Water Watch, a Washington, D.C.-based environmental group, said too few wells were part of the study to "draw meaningful conclusions about national emissions." Companies that allowed methane measurements at their wells were likely to have removed any sources of leaks before researchers arrived.
Measurements were taken at the well so emissions lost in processing and delivering gas to customers weren't counted. The University of Texas is conducting studies to measure leakage at other points in the production and delivery process.
Using data from companies, the Environmental Protection Agency in April said that gas leaked from wells in 2011 at a rate of 0.47 percent, compared with 0.42 percent in Monday's study.
The University of Texas found leakage at the initial stage of tapping a well when drilling fluids and sand used in hydraulic fracturing, or fracking, returns to the surface was less than found by the EPA. Leakage from equipment at the well pad such as pumps and valves was higher in the University of Texas study.
There are no emissions-control regulations for valves or connectors commonly found at oil or gas wells, according to the Environmental Defense Fund.