Natural Variations of Dissolved Methane in an Area of Accelerating Marcellus Shale Gas Development in North Central West Virginia
Sharma, Shikha; Mulder, Michon L.; Carr, Timothy R.
Groundwater samples were collected from nine aquifers overlying Marcellus Shale in north-central West Virginia. This study area lies within the 50 foot isopach of the Marcellus Shale, where shale gas drilling is expanding rapidly. However, at time of sample collection there was no active shale gas drilling in the study area. Samples were analyzed for carbon and hydrogen isotopic signatures and concentrations of dissolved methane, ethane, dissolved carbon dioxide concentrations, and carbon isotopic signatures of dissolved inorganic carbon. The dissolved methane concentrations range from 0 to 42 mg/L. Out of the 23 groundwater samples collected, 13 had methane concentrations high enough for isotopic analysis. The isotopic and geochemical data suggests that dissolved methane in the sampled groundwaters is primarily generated by deeper thermogenic sources and/or microbial sources via CO2 reduction in deeper marine formations. None of the dissolved methane lies in the domain of the microbial gas produced in near-surface fresh waters via acetate fermentation in coal beds and/or beneath landfills and marshes. Furthermore, samples with higher methane concentrations do not show a clear correlation with abandoned oil and gas wells, coalbed methane wells and/or abandoned mine lands. Plotting samples on a digital elevation model and examining curvature statistics suggest that higher methane concentrations are related to local topographic lows. We propose that methane from deeper sources is migrating into the sampled groundwater aquifers through natural fractures and faults over geological time scales.
AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013