Scientists have discovered high levels of methane above shale gas wells at a point in production not previously thought to be a significant source of emissions, according to a joint study led by Purdue and Cornell universities.
The research identified seven well pads with high emission levels, findings that could have serious implications for the evaluation of environmental impacts from natural gas production. Though high-emitting wells made up less than 1 percent of the total number of wells in the area, all were found to be in the drilling stage, a preproduction stage not usually associated with emissions, according to a release from Purdue University.
"These findings present a possible weakness in the current methods to inventory methane emissions, and the top-down approach clearly represents an important complementary method that could be added to better define the impacts of shale gas development," said Purdue professor Paul Shepson, who co-led the study with Cornell professor Jed Sparks. "This small fraction of the total number of wells was contributing a much larger large portion of the total emissions in the area, and the emissions for this stage were not represented in the current inventories."
Researchers flew above the Marcellus shale formation in southwestern Pennsylvania in a specially equipped airplane, known as the Purdue Airborne Laboratory for Atmospheric Research. The approach allowed them to identify plumes of methane gas from single well pads, as well as groups of well pads and larger regions, and to examine the production state of the wells.
"It is particularly noteworthy that large emissions were measured for wells in the drilling phase, in some cases 100 to 1,000 times greater than the inventory estimates," Shepson said. "This indicates that there are processes occurring ... that are not captured in the inventory development process. This is another example pointing to the idea that a large fraction of the total emissions is coming from a small fraction of shale gas production components that are in an anomalous condition."
A paper detailing the results was published in the Proceedings of the National Academy of Sciences.
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