Marcellus Shale gas cleaner than coal, CMU study says
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Burning Marcellus Shale gas instead of coal to generate electricity could reduce emissions of climate change-producing greenhouse gases by 20 to 50 percent, a recent Carnegie Mellon University study concluded.
The study, published Aug. 5 in the peer-reviewed "Environmental Research Letters," also found that Marcellus Shale gas has only a marginally larger greenhouse gas footprint when compared with conventional natural gas production.
This was said to be largely due to emissions related to the transportation and treatment of millions of gallons of water used to hydraulically fracture the rock and release the gas.
"Shale gas is better than coal when it comes to electricity generation," said Paulina Jaramillo, an assistant research professor in CMU's Engineering and Public Policy Department and one of six authors of the study. "We looked at the life cycle of gas and coal emissions, and even though methane emissions from gas are higher than from coal, the combustion emissions from coal really overwhelm them."
The study's findings estimating the life cycle greenhouse gas emissions of the two fossil fuels is different than a Cornell University study in April that said shale gas methane emissions are as harmful or more harmful than carbon dioxide emissions from coal combustion.
But the Cornell study uses different assumptions for drilling, fugitive gas emissions and power plant combustion efficiencies. It's also based on a 20-year global warming potential for greenhouse gas emissions instead of the CMU study's 100-year time frame.
Ms. Jaramillo said the shorter time frame of the Cornell study gives more weight to methane emissions, reducing the environmental advantage of gas as a fuel.
Carbon dioxide emissions can stay in the atmosphere 10 times as long as methane, but methane can have more of an effect in the short term.
The CMU study's wide range of emissions reductions from Marcellus -- between 20 and 50 percent -- was necessary, Ms. Jaramillo said, because of the uncertainty of how much gas each Marcellus well will produce during its lifetime. If per-well gas production is lower, that means higher amounts of emissions per unit of gas produced.
First Published August 20, 2011 12:00 am
