A newly released study calls into question EPA methane leakage rates reported for unconventional oil and gas plays but also says more research is needed. In findings that suggest regional leakage rates of methane are much higher than federal estimates, a new analysis concludes that methane emissions from two of the nation's fastest-growing oil and gas production regions-the Bakken and Eagle Ford shale formations-saw sharp increases in emissions equivalent to 9-10 percent of the energy produced from the formations as drilling intensified late in the last decade.

The study, published October 6 on the web site of the American Geophysical Union, used satellite data compiled from 2006-2011 to estimate the level of methane leaks from the Bakken and Eagle Ford plays as oil and gas production in the formations increased sharply due to the use of horizontal drilling and hydraulic fracturing, or fracking, over the period.

The research team, comprising scientists from the University of Bremen in Germany, the University of Maryland and the NERC Center for Ecology and Hydrology in the United Kingdom, compared the level of methane emissions seen in 2006-2008-when fracking began to get underway-to emissions seen in 2009-2011, when production from fracked oil and gas wells skyrocketed in the Bakken, located in North Dakota, and Eagle Ford, located in Texas.

The team found that compared to the first three-year period, emissions in the Bakken increased by 990,000 metric tons per year in the second three-year period. In the Eagle Ford, emissions in 2009-2011 rose by 530,000 metric tons compared to 2006-2008.

The study found these emission increases, relative to the respective increase in oil and gas production in the formations, correspond to leakage rates of 10.1 percent of production in the Bakken, and 9.1 percent of production in the Eagle Ford.

Methane leakage rates from oil and gas production are important from a climate perspective because the rapid increase in gas production from shale gas wells and the associated reduction in gas prices have led many electric utilities to sharply increase their use of gas, rather than coal, to generate electricity.

Gas producers trumpet the fact that gas, when burned in a power plant, emits roughly half as much carbon dioxide (CO2)-the main greenhouse gas-per unit of electricity as coal, which makes gas an attractive policy option for responding to global warming.

However, methane-the primary constituent of natural gas-is a highly potent greenhouse gas. Over the course of a century, methane is 34 times more effective in trapping atmospheric heat than CO2, and during its first 20 years in the atmosphere methane is even more potent at trapping heat.

The Obama administration is considering requiring reductions in methane from oil and gas industry activities. However, estimates by the Environmental Protection Agency of methane leakage rates from oil and gas operations appear to be substantially lower than those suggested by the October 6 study and other recent research.

As the October 6 study notes, the latest estimate of methane leakage rates from natural gas systems reported by EPA in the 2011 U.S. Greenhouse Gas Emissions Inventory puts methane leakage at 1.2 percent of gross U.S. gas production. Previous EPA estimates put leakage rates at 1.4 percent (2010) and 2 percent (2009).

An influential study published in April 2012 in the journal Proceedings of the National Academy of Sciences concluded that as long as methane leakage from oil and gas operations remains below 3.2 percent of production, new gas-fired combined cycle plants would reduce climate impacts compared to new coal plants. If leakage rates exceed 3.2 percent of production, however, the resulting emissions overwhelm the benefit from reduced emissions resulting from the use of gas-rather than coal-for electricity generation.

A number of other recent scientific studies have cast doubt on EPA's methane leakage estimates, which are derived from emission factors developed by the agency using decades-old data provided by the industry. The studies say the EPA estimates sharply understate the amount of methane leaking to the atmosphere from oil and gas drilling and from processing and transporting the fuels.

A study published October 9 in the online version of the journal Geophysical Research Letters that focuses on the San Juan Basin in New Mexico, where there is extensive natural gas, oil, coal and coalbed methane production, found that methane emissions from the region in 2012 were nearly twice as high as estimated by EPA and three times higher than estimated in a respected European emissions inventory.

In addition, a February synthesis of more than 200 studies of methane emissions from U.S. natural gas systems concluded that EPA's inventory understates total U.S. methane emissions by at least 50 percent, but found releases from fracking activities account for only a modest amount of the extra methane emissions.

Other recent studies also have found that methane emissions occurring during the completion phase of a fracked shale gas well are relatively modest compared to releases from pneumatic devices and other equipment used by oil and gas producers to gather and process gas.

The authors of the October 6 study said their findings indicate that methane emissions from the Bakken and Eagle Ford formations also are underestimated in EPA's emission inventory.

"Further studies are needed to provide tighter constraints on fugitive [methane] emissions and to investigate to what extent the high leakage rates obtained in this and other recent studies are representative for the entire North American oil and gas producing sector," the study said. "Accurate evaluation of the impact and sustainability of unconventional oil and gas production across the globe is essential for the development of wise environmental and energy policy."

Learn more about IHS The Energy Daily.

This article was published by S&P Global Commodity Insights and not by S&P Global Ratings, which is a separately managed division of S&P Global.