title: Searching for anomalous methane in shallow groundwater near shale gas wells.
abstract: Since the 1800s, natural gas has been extracted from wells drilled into conventional reservoirs. Today, gas is also extracted from shale using high-volume hydraulic fracturing (HVHF). These wells sometimes leak methane and must be re-sealed with cement. Some researchers argue that methane concentrations, C, increase in groundwater near shale-gas wells and that "fracked" wells leak more than conventional wells. We developed techniques to mine datasets of groundwater chemistry in Pennsylvania townships where contamination had been reported. Values of C measured in shallow private water wells were discovered to increase with proximity to faults and to conventional, but not shale-gas, wells in the entire area. However, in small subareas, C increased with proximity to some shale-gas wells. Data mining was used to map a few hotspots where C significantly correlates with distance to faults and gas wells. Near the hotspots, 3 out of 132 shale-gas wells (~2%) and 4 out of 15 conventional wells (27%) intersect faults at depths where they are reported to be uncased or uncemented. These results demonstrate that even though these data techniques do not establish causation, they can elucidate the controls on natural methane emission along faults and may have implications for gas well construction.
authors.affiliation: College of Information Sciences and Technology, The Pennsylvania State University, University Park, PA 16802, United States. Electronic address: jessieli@ist.psu.edu.
authors.forename: Zhenhui
authors.initials: Z
authors.lastname: Li
authors.affiliation: Department of Statistics, The Pennsylvania State University, University Park, PA 16802, United States.
authors.forename: Cheng
authors.initials: C
authors.lastname: You
authors.affiliation: Earth and Environmental Systems Institute and Department of Geosciences, The Pennsylvania State University, University Park, PA 16802, United States.
authors.forename: Matthew
authors.initials: M
authors.lastname: Gonzales
authors.affiliation: Earth and Environmental Systems Institute and Department of Geosciences, The Pennsylvania State University, University Park, PA 16802, United States.
authors.forename: Anna K
authors.initials: AK
authors.lastname: Wendt
authors.affiliation: College of Information Sciences and Technology, The Pennsylvania State University, University Park, PA 16802, United States.
authors.forename: Fei
authors.initials: F
authors.lastname: Wu
authors.affiliation: Earth and Environmental Systems Institute and Department of Geosciences, The Pennsylvania State University, University Park, PA 16802, United States. Electronic address: sxb7@psu.edu.
authors.forename: Susan L
authors.initials: SL
authors.lastname: Brantley
mesh_terms: D060587:Groundwater / Q000737:chemistry*; D008697:Methane / Q000032:analysis*; D059206:Natural Gas / Q000032:analysis*; D061329:Oil and Gas Fields; D010414:Pennsylvania; D014874:Water Pollutants, Chemical / Q000032:analysis*; D060986:Water Wells
chemical_list: D059206:Natural Gas; D014874:Water Pollutants, Chemical; D008697:Methane
keywords: Data mining; Groundwater; Hydraulic fracturing; Methane