The natural gas bonanza brought about by unconventional drilling may be displacing coal and diesel as a "cleaner" fuel, but methane leaks from the surge in drilling and processing destroy that advantage, according to the environmental think tank World Resources Institute (WRI).
"The rapid expansion of natural gas development in the United States has been a double-edged sword," wrote WRI's James Bradbury and his colleagues in the working paper "Clearing the Air: Reducing Upstream Greenhouse Gas Emissions from U.S. Gas Systems."
"While natural gas supporters are quick to point out its economic benefits and green attributes -- natural gas produces roughly half the carbon dioxide emissions of coal during combustion -- this isn't the whole story," said the researchers. "Natural gas comes with environmental consequences, including risks to air and water quality."
Fugitive methane emissions, which are 25 times more potent than carbon dioxide over a 100-year time frame, contribute to climate change and "undercuts the climate advantage" that gas has over coal and diesel, according to the report. WRI said it is focused on the "intersection of the environment and socioeconomic development."
Reports vary widely on the actual extent of fugitive emissions from gas exploration and development.
Last year, a joint report by America's Natural Gas Alliance and the American Petroleum Institute said methane emissions from gas wells were half of what the U.S. Environmental Protection Agency (EPA) estimated in 2010 (see Shale Daily, June 6, 2012). Companies also dispute the amount of methane emissions calculated by EPA; Devon Energy Corp. in March quit a voluntary gas well emissions data gathering program run by EPA because the data was "irresponsibly and inaccurately used to justify costly regulations" (see Shale Daily, March 13, 2012). The EPA Inspector General also has found problems with how government air emissions data is calculated (see Shale Daily, Feb. 25).
However, some estimates put U.S. methane leakage rates at 2-3% of total production, with estimates as high as 7%, said the WRI researchers.
"To put that in perspective, at a 2% leakage rate, more than 6 million metric tons of methane escape into the atmosphere in one year -- an amount equivalent to the annual emissions of roughly 120 million cars," they said.
Reducing the current methane leakage rate by two-thirds, or about 1% or less of total production, ensures that switching from diesel or coal to natural gas "provides a net climate benefit over any time horizon. Furthermore, we find that we can reach the 1% target through existing state and federal policies and the widespread use of cost-effective technologies."
First, start with "green completions," said the researchers. For instance, although they've been criticized by the industry, the EPA's new source performance standards, finalized last year, aim to reduce volatile organic compounds and air toxics, but they also have a co-benefit of reducing fugitive methane, said Bradbury.
"The rule requires 'green completions' for all hydraulic fracturing operations, ensuring that methane emissions are no longer intentionally vented from shale gas wells" (see Shale Daily, Aug. 20, 2012; July 29, 2011). "Our analysis finds that the rule will reduce total upstream methane emissions by 17% by 2015 and 29% by 2035," said Bradbury.
Three additional emissions-control technologies for new and existing wells and equipment also may help significantly, the report said.
"Using plunger lift systems, switching the existing stock of high-bleed pneumatic devices to low-bleed equivalents, and using methane leak detection and repair technologies at processing plants and compressor stations can reduce emissions by another 30%, bringing the overall leakage rate down to just over 1%. These technologies are extremely cost-effective, paying for themselves in three years or sooner."