image: Erica Barth-Naftilan prepares to sample a groundwater monitoring well adjacent to a gas well pad. view more
Credit: PNAS
Researchers report methane levels in groundwater during the course of hydraulic fracturing operations in the Marcellus Shale. With the growth of unconventional oil and gas development, concerns over the risks posed by attendant processes to groundwater resources have arisen. To better assess such risks, James Saiers and colleagues installed eight monitoring wells (MWs) in Susquehanna County, Pennsylvania, and regularly sampled groundwater over a 2-year period during which seven horizontal gas wells were drilled and began production nearby. Shortly after the start of drilling, pressures in hilltop MWs adjacent to the well pads abruptly dropped, then spiked before returning to normal levels over approximately 24 hours. A similarly abrupt pressure jump occurred following a well casing rupture. Nevertheless, methane concentrations in hilltop MWs never rose above 0.12 mg/L, 65 times lower than the regulatory action level. For MWs in valleys above gas well laterals, methane levels increased considerably over the course of the study period. However, isotopic data, hydrocarbon compositions, and other evidence suggested that the methane did not come from the Marcellus Shale and was unlikely to be due to gas well drilling and hydraulic fracturing operations. Groundwater salinity increased with methane concentration, suggesting that the increasing methane concentration reflected natural shifts in aquifer recharge that altered the mixing between methane-free shallow groundwater and naturally methane-rich deep groundwater, according to the authors.
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Article #17-20898: "Methane in groundwater before, during, and after hydraulic fracturing of the Marcellus Shale," by Erica Barth-Naftilan, Jaeeun Sohng, and James E. Saiers.
MEDIA CONTACT: James E. Saiers, Yale University, New Haven, CT; tel: 203-432-5121; e-mail: james.saiers@yale.edu
Journal
Proceedings of the National Academy of Sciences