High levels of the greenhouse gas methane were found above shale gas wells at a production point not thought to be an important emissions source, according to a study jointly led by Purdue and Cornell universities. The findings could have implications for the evaluation of the environmental impacts from natural gas production.
The study, which is one of only a few to use a so-called “top down” approach that measures methane gas levels in the air above wells, identified seven individual well pads with high emission levels and established their stage in the shale-gas development process.
The high-emitting wells made up less than 1 percent of the total number of wells in the area and were all found to be in the drilling stage, a preproduction stage not previously associated with significant emissions.
The researchers flew above the Marcellus shale formation in southwestern Pennsylvania in the Purdue Airborne Laboratory for Atmospheric Research, a specially equipped airplane. The aircraft-based approach allowed researchers to identify plumes of methane gas from single well pads, groups of well pads and larger regional scales 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,” said Paul Shepson, a professor of chemistry and earth atmospheric and planetary sciences at Purdue who co-led the study with Jed Sparks, a professor of ecology and evolutionary biology at Cornell. “This indicates that there are processes occurring – e.g. emissions from coal seams during the drilling process – 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 will be published in the Proceedings of the National Academy of Sciences on Monday (April 14). The David R. Atkinson Center for a Sustainable Future at Cornell University funded this research.
“We need to develop a way to objectively measure emissions from shale gas development that includes the full range of operator types, equipment states and engineering approaches,” Shepson said. “A whole-systems approach to measurement is needed to understand exactly what is occurring.”