by James A. Pardo and Brandon H. Barnes
Shale natural gas production emits significantly less fugitive methane than previously thought, concluded researchers at the Massachusetts Institute of Technology (MIT) in a November 26, 2012, study published in Environmental Research Letters. According to the researchers, "it is incorrect to suggest that shale gas-related hydraulic fracturing has substantially altered the overall [greenhouse gas] intensity of natural gas production."
Methane has been singled out as one of the most powerful greenhouse gases (GHG) because of its "global warming potential" – or the relative heat trapped in the atmosphere by a gas – which is 20 times greater than that of carbon dioxide. Fugitive methane emissions are losses of methane gas that may occur during flowback (the return of fluids), during drill-out following fracturing, and during well-venting to alleviate well-head pressure. Fugitive emissions can also occur as a result of equipment leaks, transportation or storage losses, and processing losses, but in much smaller quantities.
An earlier study by Cornell University professor Robert Howarth, which garnered much media attention, reported that shale gas production had a lifetime carbon footprint greater than coal production, mainly as a result of fugitive methane emissions that Howarth had estimated to be as great as 4,638 Mg per well. In contrast, the MIT study determined that actual fugitive methane emissions average approximately 50 Mg per well after taking into account flaring and green completions technology, both of which are widely used by industry and required under most state regulatory regimes (as well as under new Environmental Protection Agency rules). The MIT researchers evaluated actual production data from approximately 4,000 horizontal shale natural gas wells, and found a potential for about 228 Mg of fugitive methane emissions per well. The researchers cautioned that estimates about fugitive methane emissions had been "inappropriately used in analyses of the GHG impact of shale gas" insofar as actual emissions are reduced — by an average of 178 Mg per well — by flaring and green completion technology.
Hydraulic fracturing stakeholders need to understand the body of publicly available science, as a growing body of research will inform how EPA and other state and federal regulatory agencies will regulate the industry.