Why a Prominent Report May Underestimate Methane Emissions

A study published yesterday in Energy Science & Engineering contends that a measurement tool at the heart of in an important recent analysis of methane leaks from fracking sites was improperly used and thus the results of that study greatly underestimate methane emissions. There are other reasons to think that the study in question, by Prof. David Allen at the University of Texas, Austin, and supported by the Environmental Defense Fund, lowballs the amount of global warming pollution from fracking sites.

A study published yesterday in Energy Science & Engineering contends that a measurement tool at the heart of in an important recent analysis of methane leaks from fracking sites was improperly used and thus the results of that study greatly underestimate methane emissions. There are other reasons to think that the study in question, by Prof. David Allen at the University of Texas, Austin, and supported by the Environmental Defense Fund, lowballs the amount of global warming pollution from fracking sites.

In 2013, Prof. Allen and other researchers from the University of Texas, Austin, worked in collaboration with the Environmental Defense Fund and oil and gas companies to measure methane emissions from selected drilling sites. The study reported very low average leakage rates and, when added to Environmental Protection Agency estimates for methane emissions from other stages of natural gas production, led the researchers to conclude that just 0.42 percent of gas produced leaked into the atmosphere.

In addition to the critique published in Energy Science & Engineering, there are three other reasons to think that the Allen study underestimates methane emissions.

First, the emissions estimates are based on a small sample size (just 40 well locations or activities) and were carried out at facilities selected by oil and gas companies with an incentive to minimize estimates of leakage. Other research has suggested that a large share of fugitive emissions may come from a small number of faulty pieces of equipment – precisely the kinds of equipment likely to be screened out of a small, hand-picked group of wells. One study measured leaks from 75,000 individual components used at natural gas well sites, compressor stations and gas processing plants, revealing that 0.06 percent of the devices were responsible for 58 percent of the documented pollution. In other words, even if more than 99 percent of components operate perfectly, emissions still can be high because of the failure of a handful of devices. As a result, the Allen study may document how low emissions could be in a best case scenario, not what emissions are in standard practice or on average.

Second, the EPA data from which downstream emissions were calculated after the gas left drilling sites likely underestimate emissions. A separate analysis by researchers from Stanford, the National Renewable Energy Laboratory (NREL), the University of Michigan and other institutions that compared measured emissions reported in multiple studies to EPA’s national greenhouse gas inventory found that actual emissions were 50 percent greater than reported in the inventory.

Third, the emission estimates could be missing other leak sources – for example, from abandoned wells. A 2014 study led by Mary Kang from Princeton University measured methane flows from abandoned wells in Pennsylvania. If leakage from these Pennsylvania wells is assumed to be representative of leakage from the approximately 3 million abandoned wells in the U.S., methane from abandoned wells could increase Allen’s estimate by more than 10 percent. Allen’s study and other studies that base emission estimates on short-term analyses of specific gas well components likely miss emissions that can only be found using broader and longer-term methodologies.

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Elizabeth Ridlington

Associate Director and Senior Policy Analyst, Frontier Group

Elizabeth Ridlington is associate director and senior policy analyst with Frontier Group. She focuses primarily on global warming, toxics, health care and clean vehicles, and has written dozens of reports on these and other subjects. Elizabeth graduated with honors from Harvard with a degree in government. She joined Frontier Group in 2002. She lives in Northern California with her son.

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