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MIT: Fugitive methane emissions from shale gas wells overstated

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Fugitive methane emissions from completion of shale gas wells have been overstated, according to a new study from the Massachusetts Institute of Technology.

These emissions may be significant, at 3.6 percent of fugitive emissions from the industry, according to "Shale gas production: potential versus actual greenhouse gas emissions," published Nov. 26 in the peer-reviewed journal Environmental Research Letters.

But field practices are managing more of the potential emissions than other researchers have asserted.

It was long and widely said that natural gas emits half the greenhouse gases of coal, a generalization based on a comparison of carbon dioxide emissions when the two are burned for electricity.

But a 2011 study from Robert Howarth of Cornell University looking at the "lifecycle" extraction–to–end use greenhouse gas footprint of shale gas set off a public debate.

Howarth's study found that, when operators who use high-volume hydraulic fracturing into shale formations "complete" their wells — that is, make them ready for production — they release large volumes of methane, a far more potent greenhouse gas than carbon dioxide.

The study estimated that, including methane released during completion and methane leaked afterward during processing, transmission, storage and distribution, as much as 8 percent of a shale well's final volume could be lost to the atmosphere. The study concluded that the global warming potential of shale gas exceeds that of coal over a 20-year time frame and is comparable over a 100-year time frame.

While a spate of estimates since that time have ranged, generally, from 2 to 10 percent of total production volume released as fugitive emissions, scientists coming in all across that spectrum have agreed that much of the fugitive methane is released specifically during the week or so of well completion.

The MIT study disagrees.

The researchers looked at production data on 4,000 new wells in the five most productive shale formations in 2010 — Barnett, Fayetteville, Haynesville, Marcellus and Woodford shales.

Data on the key question of emissions during well completion are scarce, they acknowledged.

"Significant opaqueness surrounds real world gas handling practices in the field, and what proportion of gas produced during well completions is subject to which handling techniques," they wrote.

Howarth, they wrote, assumed that all potential fugitive emissions are vented. The U.S. Environmental Protection Agency has assumed that half of fugitive emissions are vented.

The MIT researchers themselves referenced an industry-sponsored survey of practices used at about 1,600 wells — acknowledging its industry source but noting that it is the most comprehensive study available — and supplemented that information with interviews with industry, the EPA and others.

They concluded that methane generated during well completion is captured at 70 percent of wells, flared at 15 percent and vented at only 15 percent.

That reduces fugitive emissions from an average potential of 228 megagrams of methane per well to their estimate of 50 megagrams per well.

Overall, according to their calculations, 0.4 percent to 1.0 percent of a well's ultimate production volume is lost through fugitive emissions.

An April 2012 rule from the EPA requires operators to flare their gas during completion or to capture it rather than venting it.

But this study suggests that shale well completion is not necessarily a hot spot for controlling gas-industry emissions — that emissions come, rather, from points throughout the gas production, processing, transport and delivery processes.

"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 greenhouse gas intensity of natural gas production," they authors wrote.