Identification of the Causes and Extent of Elevated Methane Concentrations in the Groundwater of Eastern Kentucky
Elevated levels of methane (CH4) in groundwater can lead to accumulation of gas in enclosed areas, resulting in potentially explosive environments. A recent study in northeastern Kentucky identified dissolved methane to be a widespread phenomenon, with 28% (n= 51) of analyzed domestic wells in the “warning” and “immediate action” level ranges. The wells with nearby mining activities were more likely to have elevated methane levels (CH4 > 1 mg/L). In contrast, a study in southeastern Kentucky observed significantly lower concentrations and an inverse correlation between CH4 concentration and proximity to mining activities. CH4 concentrations showed no correlation with distance to oil and gas wells in either study. However, recent evaluations of horizontal drilling and hydraulic fracturing as options to develop two major oil and gas plays in eastern Kentucky have increased interest in understanding baseline groundwater chemistry in the overlying Pennsylvanian sandstone aquifers. Drilling occurs at shallow depths (<600m) in the Devonian Berea Sandstone and is expected to occur at depths of 2000m to more than 4000m in the Cambrian Rogersville Shale. Both plays cover an area with a long history of resource development, a dissected topography and limited hydrologic communication. Nevertheless, local trends in chemical parameters and different solute availability could account for some of the observed differences in CH4. We sampled 18 groundwater wells for bulk chemistry and isotopic composition within the ~60-km region between previous studies. Initial results of major cations, anions, dissolved gas concentrations, δ13CDIC, δ2H, δ18O, and δ13CCH4 suggest a biogenic source of methane for wells where sulfate (SO42-) concentrations are low. δ34SSO4 and δ18OSO4 data should elucidate sulfate sources for a subset of wells with high sulfate. Additionally, we compile trends in the chemical and isotopic composition of groundwater in Eastern Kentucky and their relation to CH4. Further geospatial and statistical analysis of data in relation to anthropogenic activities (mining, oil and gas development) should elucidate CH4 and SO42- dynamics and any processes associated. We anticipate this study will improve our understanding of groundwater geochemical zones and systems, provide baseline information for groundwater quality and dissolved gases, and serve as a reference to evaluate contamination, if any, from previous and future resource development in Eastern Kentucky.
AAPG Datapages/Search and Discovery Article #90373 © 2019 AAPG Eastern Section Meeting, Energy from the Heartland, Columbus, Ohio, October 12-16, 2019