Study Sheds Light on the Environmental Impact of Shale Gas

• The view that methane leaks render shale gas "worse than coal" has been further undermined by the release of a new study based on actual measurements at hundreds of gas wells.
• Previous estimates of methane leakage relied on modeling or extrapolation from remote measurements. The University of Texas study addresses these shortcomings.

Since the late 1990s natural gas has been identified by both energy experts and environmentalists as a likely "bridge fuel" to facilitate the transition to cleaner energy sources. This view has recently been challenged by suggestions that methane leakage from natural gas systems--particularly from shale gas development--might be significant enough to negate the downstream climate benefits of switching to natural gas. The results of a new study from the University of Texas, sponsored by the Environmental Defense Fund (EDF) and nine energy companies, should alleviate many of those concerns.

In order to understand why indications of potential natural gas leakage rates well above the previously assumed level of around 1% would cast doubt on the environmental benefits of gas, a brief primer on greenhouse gases (GHGs) is necessary. When present in the atmosphere, these gases contribute to global warming by trapping infrared radiation that would otherwise be emitted to space. Carbon dioxide is the primary GHG implicated in climate change. It currently makes up roughly 400 parts per million (ppm)--equivalent to 0.04%--of earth's atmosphere and is increasing by around 2 ppm per year.

The main constituent of natural gas is methane. Although atmospheric concentrations of methane are much lower than that of CO2, totaling less than 2 ppm, pound for pound it is a much stronger GHG. Its "global warming potential" is 25 times higher than CO2's over a 100-year time horizon, and even higher on a shorter time span. While most atmospheric methane has been traced to natural or agricultural sources, a large increase in atmospheric methane from natural gas production could overwhelm the undisputed downstream emissions benefits of gas in  electricity generation, compared to coal.

Several academic studies raised precisely this concern with regard to natural gas produced from shale by hydraulic fracturing, or "fracking", starting with a widely-publicized paper from a professor at Cornell University in 2010. This work relied on estimates and limited data from early shale production to arrive at a conclusion that shale gas wells leak 3.6-7.9% of their cumulative output. A more recent series of studies from the National Oceanic and Atmospheric Administration (NOAA) and the University of Colorado Boulder used airborne remote sensing techniques to calculate leakage rates similar to Professor Howarth's.

Other studies from groups as diverse as IHS CERA, Carnegie Mellon University, and Worldwatch Institute and Deutsche Bank addressed the same question but arrived at much lower leakage rates and impacts. And earlier this year the US Environmental Protection Agency reduced its previous estimate of overall natural gas leakage to a figure equivalent to 1.7%.

However, until now all scientific studies of this issue--on both sides--were based on limited data, or on indirect measurements obtained at a significant distance from actual production sites. They relied heavily on assumptions about what was happening at large numbers of gas wells, in the absence of direct observations at these sites.

That's what makes the UT study so significant; it is based on a wealth of data from actual, on-site measurements at "190 production sites throughout the US, with access provide by nine participating energy companies." That translates to roughly 500 shale gas wells in different stages of development and production. 

Overall, for the segment of the gas lifecycle they investigated, the UT team found methane emissions that were lower than EPA's latest estimates.  Emissions from "completion flowbacks" were  98% lower, partially offset by somewhat higher observed leaks from valves and other equipment. Although this study did not measure emissions from the entire gas lifecycle, including pipelines, it would be very hard to reconcile their observed average leakage rate of 0.4% of gross gas production with leakage estimates as high as those embraced by many of shale's critics.

Immediate criticisms of this study also missed several crucial points. First, without the industry involvement that they characterized as a "fatal flaw", access on this scale for direct measurements at production sites--surely the gold standard for emissions studies compared to estimates based on assumption-laden models--would have been difficult or impossible to obtain. More importantly, they also ignored the fact that the principal sources of methane emissions found by the UT team involved valves and equipment by no means unique to shale development, many of which should be amenable to hardware improvements or different technology choices.

While the UT team and their sponsors at EDF stated clearly that more work needs to be done to measure methane emissions from other parts of the gas value chain, the current paper convincingly dispels the notion that the emissions from shale gas development are inherently much higher than those for gas produced from vertical wells in conventional oil and gas reservoirs. Since shale gas already accounts for over a third of US natural gas production and is widely expected to dominate future production, that result has large implications for the environmental benefits of further fuel switching and other applications for natural gas.

A different version of this posting was previously published on the website of Pacific Energy Development Corporation.