While many of these reports studied the amount of potential emissions associated with the hydraulic fracturing process, the MIT researchers stressed that this is only part of the puzzle. Consideration must also be given to how this gas is handled at the drilling sites, the MIT researchers said.

While increased efforts need to be made to reduce emissions from the gas industry overall, the production of shale gas has not significantly increased total emissions from the sector. It’s unrealistic to assume all potential emissions are vented, not least because some states have regulations requiring flaring as a minimum gas handling method.

—Francis O’Sullivan, researcher at MIT’s Energy Initiative and the lead author

Sergey Paltsev, the study’s co-author and the assistant director for economic research at the MIT Joint Program on the Science and Policy of Global Change, says companies also have an economic reason for wanting to capture this “fugitive” gas.

When companies vent and flare methane they are losing gas that they could have captured and sold. When we compared the cost of installing the right equipment to capture this gas to the loss in revenue if it isn’t captured, we found that the majority of shale wells make money by capturing the potential fugitive emissions.

—Sergey Paltsev

In talking with industry representatives and officials at the US Environmental Protection Agency (EPA), O’Sullivan and Paltsev found that companies are already capturing about 70% of potential fugitive emissions. In factoring that into their analysis, the researchers find emissions from shale gas production to be strikingly lower than previous estimates of potential emissions.

Their analysis was based on data from each of the approximately 4,000 wells drilled in the five main US shale drilling sites during 2010. Wells in two of those sites, Texas’ Barnett shale and the Haynesville shale on the Texas-Louisiana boarder, had been studied by Robert Howarth from Cornell University last year when he looked at potential emissions released by the industry.

The Howarth study garnered much attention because it claimed the greenhouse gas footprint of shale gas was larger than that of conventional gas, oil, and, over a 20-year time frame, coal. That study, however, used very limited well datasets, the MIT team noted.

In studying potential emissions, Howarth found 252 Mg of methane emissions per well in the Barnett site and 4,638 Mg per well in the Haynesville site. The MIT researchers, using their comprehensive well dataset, found that the potential emissions per well in the Barnett and Haynesville sites were 273 Mg and 1,177 Mg, respectively. When accounting for actual gas handling field practices, these emissions estimates were reduced to about 35 Mg per well of methane from an average Barnett well and 151 Mg from an average Haynesville well.

Taking actual field practice into account, we estimate that in 2010 the total fugitive GHG emissions from US shale gas-related hydraulic fracturing amounted to 216 Gg CH₄. This represents 3.6% of the estimated 6002 Gg CH₄ of fugitive emissions from all natural gas production-related sources in that year (EPA 2012a, 2012b). The entire natural gas value chain is estimated to have produced 10259 Gg CH₄ of fugitive emissions in 2010, or about 3.1% of the nation’s total GHG inventory (EPA 2012a, 2012b). Thus under a goal of GHG reduction it is clear that increased efforts must be made to reduce fugitive losses from this system.

However, it is also clear is that the production of shale gas and specifically, the associated hydraulic fracturing operations have not materially altered the total GHG emissions from the natural gas sector. Furthermore, for the vast majority of contemporary shale gas wells, the revenues gained from using reduced emissions completions to capture the gas produced during a typical flowback cover the cost of executing such completions.

—O’Sullivan and Paltsev (2012)

According to Adam Brandt, an Assistant Professor at Stanford University, this analysis “provides an important contribution to the literature by greatly improving our understanding of potential shale gas emissions using a very large dataset.”

Previous studies used much smaller and more uncertain datasets, while O'Sullivan and Paltsev have gathered a much larger and more comprehensive industry dataset. This significantly reduces the uncertainty associated with potential emissions from shale gas development.

—Adam Brandt

A US Department of Energy study released in August confirmed that while electricity generated by gas produces half the emissions of coal generation, natural gas production makes up 3% of the nation’s total emissions. While the overall benefits far outweigh the small increases during production, Paltsev believes the EPA’s efforts to reduce those emissions through new air quality standards are a “step in the right direction.”

Resources

• Francis O’Sullivan and Sergey Paltsev (2012) Shale gas production: potential versus actual greenhouse gas emissions. Environmental Research Letters doi: 10.1088/1748-9326/7/4/044030