Greenhouse gas (GHG) emissions from shale gas well hydraulic fracturing (fracking) operations are significantly lower than previously estimated, according to researchers at the Massachusetts Institute of Technology (MIT).

Data collected from each of the about 4,000 horizontal shale gas brought online in 2010 indicates that 900 gigagrams (Gg) of potential fugitive methane (CH4) emissions were generated by the operations, but that figure is "inappropriately used in analyses of the GHG impact of shale gas," according to a report by Francis O'Sullivan and Sergey Paltsev, which was published in Environmental Research Letters.

"In fact, along with simply venting gas produced during the completion of shale gas wells, two additional techniques are widely used to handle these potential emissions: gas flaring and reduced emission 'green' completions," the researchers said. "The use of flaring and reduced emission completions reduce the levels of actual fugitive emissions from shale well completion operations to about 216 Gg CH4, or 50 Mg CH4 per well, a release substantially lower than several widely quoted estimates.

"Although fugitive emissions from the overall natural gas sector are a proper concern, it is incorrect to suggest that shale gas-related hydraulic fracturing has substantially altered the overall GHG intensity of natural gas production."

It is "unrealistic" to assume all potential emissions are vented, according to O'Sullivan, "not least because some states have regulations requiring flaring as a minimum gas-handling method."

The report further discounts the results of research conducted at Cornell University in 2011 which concluded that methane leaked during shale natural gas drilling and production activities is more than that seen from wells in conventional plays and is a more serious threat to global warming than carbon dioxide released from coal (see NGI, April 18, 2011). In that study, Cornell ecologist Robert Howarth estimated that as much as 8% of the methane in shale gas leaks into the air during the lifetime of a fracked shale gas well, which is up to twice what escapes from conventional gas production.

Howarth's study had been blasted by pro-industry groups and clean transportation advocate T. Boone Pickens, and a series of subsequent studies criticized Howarth for overstating CH4 emissions and said natural gas has fewer GHG emissions than coal (see NGI, May 16; April 25). Last November three Cornell researchers said their colleagues' controversial study contained serious flaws and should be revisited (see NGI, Dec. 5, 2011).

Howarth and his research team have stood by their claim that shale gas has a larger GHG footprint than conventional gas and oil or coal, and thus would be an unsuitable bridge fuel (see NGI, Jan. 23).

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