A Duke University study released Monday found high levels of leaked methane in well water collected near shale gas drilling and hydraulic fracturing (fracking) sites in the Marcellus Shale play. However, Duke researchers said there was no evidence that fracking fluids contaminated the water wells.

And the Scotland-based Wood Mackenzie disputed recent findings by Cornell University that the methane emissions during the completion process of fracked wells exceeds that of coal.

Four Duke University scientists collected and analyzed water samples from 68 private groundwater wells across five counties in northeastern Pennsylvania and New York, which overlay the Marcellus Shale play. "We found measurable amounts of methane in 85% of the samples, but levels were 17 times higher on average in wells located within a kilometer of active hydrofracking sites," said Stephen Osborn, post-doctoral research associate at Duke's Nicholas School of Environment. The contamination was observed primarily in Bradford and Susquehanna counties in Pennsylvania.

According to the study's findings, "at least some of the homeowners who claim that their wells were contaminated by shale gas extraction appear to be right," said Robert B. Jackson, director of Duke's Center on Global Change.

The study, however, found no signs of contamination from chemical-laden fracking fluids, which are injected into gas wells to help break up shale deposits, or from wastewater that is extracted back out of of the wells after the shale has been fractured, the researchers said. The peer-reviewed study was published Monday in the Proceedings of the National Academy of Sciences.

Methane is flammable and poses a risk of explosion, and can cause asphyxiation. The study said little research has been conducted on the health effects of drinking methane-contaminated water. It further noted that methane isn't regulated as a contaminant in public water systems under the Environmental Protection Agency's National Primary Drinking Water Regulations.

Accelerated gas drilling and fracking in the Marcellus Shale gas play in recent years have fueled concerns about well water contamination by methane, produced water and fracking fluids, the study noted. Shale gas accounts for about 15% of the natural gas currently produced in the United States.

Meanwhile, the Wood Mackenzie analysis has found that a recent study by Cornell University researchers significantly overestimated the fugitive methane emissions from unconventional natural gas wells.

Cornell researchers said that methane emissions of flowback gas during completion of fracked wells are high enough to increase the greenhouse gas footprint of shale and tight gas to levels that exceed those of coal (see Shale Daily, April 13). The Cornell research was quickly challenged by a study published by the gas industry-supported American Clean Skies Foundation (see Shale Daily,April 21).

Now Wood Mackenzie says the Cornell study overestimated the average volume of gas vented during well completion and flowback stages by 60-65% and overestimated the impact from emissions during well completions by up to 90%.

Further, "the [Cornell] study does not take into consideration recent industry trends, such as green completions, which are employed across many mature U.S. plays," Wood Mackenzie said in a new Insight report. "Green completions not only significantly reduce emissions but also allow producers to capture the value of the flowback gas, which has served to increase the adoption of practices and technologies to capture these initial volumes.

"We estimate that up to US$9 billion of incremental value can be captured from the Haynesville Shale alone by capturing early wellhead gas in the play through 2020, saving nearly 0.9 Tcf from being vented or flared."

Practices for controlling gas patch methane emissions have been evolving, and the industry has made significant strides that were not taken into account by the Cornell research, Wood Mackenzie said. For instance:

Wood Mackenzie found that green completion practices are employed in established unconventional gas plays. Operators have adopted green completions in the Barnett, Jonah, Pinedale, Wamsutter, Fayetteville and other established plays, for instance. "One key prerequisite for adoption is to have existing sales lines in place prior to completion. This typically happens once development has progressed past initial delineation, since an understanding of the reservoir properties is required to ensure installation of the correct pipeline size even before a well is tested. As operators progress from early development in emerging plays and gathering constraints ease, green completions are likely to be embraced."

The practice of estimating methane emissions from gas development will likely be an important area of study as unconventional gas development spreads to new areas and concerns over environmental impacts increase, Wood Mackenzie said. "Existing data sources for estimating these volumes will need to be improved, which could improve perception of the industry, as would, of course, continued proliferation of green completions.

"Importantly, moving from early development stages to more sustainable 'gas manufacturing,' as we expect to happen over the medium term, will allow green completions to be employed in more plays."