September 27, 2013
In a far-reaching study of fracking in several states, researchers at the University of Texas found greenhouse gas pollution during fracking to be lower than previous EPA estimates. The study re-sets a debate over the relative climate benefits for using natural gas over coal, and provides the largest-to-date amount of field-level data from active drilling sites.
Supporters of natural gas are calling the study further proof that fracking is a way to mitigate our climate impacts by replacing coal with gas.
The American Petroleum Institute said the study “shows that methane emissions are a fraction of estimates from just a few years ago.”
But the study—while setting the bar on field-level measurements—does not look like it’s ended the debate over fracking’s impact on climate.
Some climate hawks remain skeptical of the benefits of fracking, and of the results from the study—which was funded by the Environmental Defense Fund(EDF) and several oil and gas companies. The companies volunteered to allow researchers to measure methane emissions on nearly 500 wells across 190 sites. Critics have questioned how representative wells chosen by the industry are for the rest of the country’s nearly 500,000 gas wells.
The debate over fracking and climate change hinges on how much methane leaks out of wells in formations like the Marcellus shale. The country now gets about 30 percent of its natural gas from shale. To get to this gas, the company typically bores down over a mile underground, then uses horizontal drilling and hydraulic fracturing—“fracking” for short—to extract the gas.
Burning natural gas produces about half the carbon dioxide as burning coal. But when it’s released into the air, methane—the main ingredient in natural gas—is a powerful greenhouse gas. Over a short, 20 year time span, methane is 72 times more powerful than CO2 when it comes to keeping heat on the earth from escaping into space.
The “break even” mark for gas—where gas becomes better than coal in terms of greenhouse gas impacts—has been estimated at around 3 percent. Field measurements in Utah and Colorado have shown as much of 9 percent of gas leaking out of wells.
Field Evidence Shows Low Gas Leaks
But the EPA estimate for gas leakage is much lower—about 1.5 percent. At those levels, natural gas has a significantly smaller carbon footprint than coal. The study, published in the Proceedings of the National Academy of Sciences, and led by the University of Texas' David Allen, the chair of EPA’s Scientific Advisory Board, suggests the actual number could be much lower.
In particular, the study found only a very small amount of methane escaping wells during ‘completions’—a period when methane can escape into the atmosphere just after a well is fracked. The authors found the amount leaking out of the wells they studied was 48 times lower than EPA previously estimated. The study also found that leaks at other parts of the distribution process were higher than EPA estimates.
Overall, the authors estimate the total amount of methane that escapes during drilling for natural gas to be about 22 percent lower than the EPA’s estimate. Reducing the methane emissions from gas wells by one-third “would have the same climate benefit over the next 20 years as retiring another 10 percent of U.S. coal generation,” according to the EDF.
Still, the authors of the study say this isn’t the last word on the subject. Because emissions vary between well sites, and because the number of sites sampled was relatively small “extrapolating the results” the authors say, “should be done with caution.”
A Representative Sample?
Several critics, including Physicians, Scientists & Engineers for Healthy Energy,
and Bill Chameides, of Duke University, wondered if the voluntary nature of the study led the scientists to study only the ‘best’ wells.
The scientists contend they followed standard scientific practice when selecting sites to sample. They were given lists of possible sites to sample provided by the host companies. The University of Texas-based team sampled more easily in sites located in the Gulf Coast region. “For these sites, the study team randomly selected from hundreds of potential sites provided by host companies,” the authors wrote in the paper’s appendix.
Another key facet was that two-thirds of the wells studied during “completion” were using newly required methods to capture methane during drilling. These so-called ‘green completions’—which send stray methane into tanks or directly into a pipeline, will be required at almost all drilling sites by 2015, thanks to new rules on fracking from the EPA.
Chameides wrote that the key question answered by the study was not if, but can methane leaks are low during fracking. “[T]here are sites out there with very low leakage rates; in other words, the oil and gas industry is capable of running a fracking operation with very low amounts of natural gas leakage,” he wrote in the Huffington Post.
The EDF promises to dig in even farther in the future. The group has commissioned a NOAA team to conduct aerial measurements over gas-drilling sites, and will publish a total of 16 papers overall on fracking.