A long-awaited study led by the University of Texas at Austin shows that methane emissions from natural gas drilling sites are about 10 percent lower than recent estimates by the U.S. Environmental Protection Agency.
The research adds fresh fuel to the debate over whether natural gas is less carbon-intensive than coal. Although natural gas power plants emit smaller quantities of greenhouse gases than coal-fired plants, the production and distribution of natural gas release large amounts of methane, creating uncertainty about the fuel's overall climate impact. Methane is 20 to 100 times more potent than carbon dioxide as a greenhouse gas.
The new study is significant because the scientists had direct access to production sites, allowing them to measure methane emissions from hundreds of wells across the United States. Previous studies by independent scientists largely relied on data gathered on publicly accessible land close to company property.
The study had been viewed with skepticism before its release because 90 percent of the $2.3 million in funding came from nine energy companies, including Encana, Chevron and a subsidiary of ExxonMobil. The remaining 10 percent came from the Environmental Defense Fund, which, unlike many other environmental groups, has a history of working with the oil and gas industry.
The participating companies gave the researchers access to their facilities, but the scientists controlled the study design, data collection and analysis. The results were published today in the peer-reviewed journal Proceedings of the National Academy of Sciences (PNAS).
The researchers attribute the drop in methane leakage to the growing use of emissions-reducing technology. The EPA's methane inventory was based on data from 2011, but the new data were collected a year later, when more operators were using EPA-mandated controls.
"I hope one of the effects of the paper is to call attention to best practices, because it demonstrates how much more environmentally responsible you can be if you can do that," said study co-author Charles Kolb, president of Aerodyne Research, an engineering firm that specializes in air monitoring.
After measuring methane leaks from 190 sites containing more than 500 wells, the researchers extrapolated their results to a national emissions rate of 2,300 gigagrams—or 5.1 billion pounds of methane—per year. The EPA's latest survey calculates emissions of 2,545 gigagrams, or 5.6 billion pounds, per year. (One gigagram is equal to 2.2 million pounds.)
According to the EPA, petroleum and natural gas systems—a category of facilities that includes production, processing, distribution and storage but not refining—were the nation's second-biggest source of greenhouse gases in 2011, behind power plants. There are about a half-million onshore natural gas wells in the United States.
Chevron spokesman Kurt Glaubitz said the new research is "a good first step" in measuring methane emissions directly at the source. "This is an important issue for the industry, and Chevron's very pleased to be a part of this study."
Experts not involved with the study praised the research for its methods and transparency but cautioned that the results may not represent the industry as a whole.
They "had to get the companies to participate, and the companies that volunteer tend to be ones that pay attention to doing things well, because they know they're being watched and measured,” said Bruce Baizel, energy program director at Earthworks, a nonprofit that advocates for responsible oil and gas production. “I think you can view this as the best case scenario."
The study authors said they tried to get representative data by testing wells from a large number of companies across a range of geographies. "Representativeness cannot be completely assured, however, since companies volunteered, and were not randomly selected," they said in the report.
The research is one of 16 projects the Environmental Defense Fund launched to measure methane emissions across the natural gas supply chain, including compressor stations, gathering lines and storage facilities. The studies will be released over the next 18 months in peer-reviewed journals and cost a collective $18 million. The work is funded by EDF, the nine energy companies and individual donors.
The wells used in the study were produced using hydraulic fracturing, or fracking, a process where large amounts of water, sand and chemicals are injected underground to stimulate the flow of gas.
After a well is fractured, the fracking fluids flow back out of the well in a process called well completion. This step prepares the well for sustained gas production and can last anywhere from hours to weeks.