Purdue/Cornell airborne study finds unexpected levels of methane from shale gas pads in drilling stage
High levels of the greenhouse gas methane were found above shale gas wells at a point in production (i.e., drilling) not thought to be an important emissions source, according to a study jointly led by Purdue and Cornell universities. The study, which is one of only a few to use an 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% 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.
Despite their low numbers, the emissions from these well pads accounted for 4–30% of the observed regional flux. A paper detailing the results is published in the Proceedings of the National Academy of Sciences.
We identified a significant regional flux of methane over a large area of shale gas wells in southwestern Pennsylvania in the Marcellus formation and further identified several pads with high methane emissions. These shale gas pads were identified as in the drilling process, a preproduction stage not previously associated with high methane emissions. This work emphasizes the need for top-down identification and component level and event driven measurements of methane leaks to properly inventory the combined methane emissions of natural gas extraction and combustion to better define the impacts of our nation’s increasing reliance on natural gas to meet our energy needs.—Caulton et al.
Paul Shepson, a professor of chemistry and earth atmospheric and planetary sciences at Purdue, co-led the study with Jed Sparks, a professor of ecology and evolutionary biology at Cornell.
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. 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.—Paul Shepson
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. 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.—Paul Shepson
Bottom-up inventories have been produced from industry measurements of emissions from individual production, transmission and distribution components and then scaling up to create an estimate of emissions for the region. However, with thousands of wells, and a complex processing and transmission system associated with each shale basin, obtaining a representative data set is difficult, Shepson said.
The David R. Atkinson Center for a Sustainable Future at Cornell University funded this research.
Dana R. Caulton, Paul B. Shepson, Renee L. Santoro, Jed P. Sparks, Robert W. Howarth, Anthony R. Ingraffea, Maria O. L. Cambaliza, Colm Sweeney, Anna Karion, Kenneth J. Davis, Brian H. Stirm, Stephen A. Montzka, and Ben R. Miller (2014) “Toward a better understanding and quantification of methane emissions from shale gas development,” PNAS doi: 10.1073/pnas.1316546111