Water Resources Research Act Program

Details for Project ID 2013WV205B

Understanding variations in isotopic and molecular compositions of stray gas in areas of accelerating shale gas development

Institute: West Virginia
Year Established: 2013 Start Date: 2013-03-01 End Date: 2015-02-28
Total Federal Funds: $40,000 Total Non-Federal Funds: $80,168

Principal Investigators: Shikha Sharma

Abstract: There is rising concern that stimulation of hydraulic fractures during Shale gas drilling or leaky well casings can allow dissolved methane (commonly referred to as stray gas) to escape into public drinking water supplies which can be an explosion and fire hazard. However, in coal mining areas of the Appalachians methane leaks can also originate from shallow gas bearing strata, coalbeds and storage gas fields. Therefore, an increase in methane concentrations alone cannot always be attributed to Marcellus Shale drilling activity. The molecular composition along with the carbon/hydrogen isotopic signatures of methane and higher hydrocarbons have been used by a few researchers for stray gas identification in the shale gas drilling areas of Appalachia (e.g. Laughrey and Baldassarey 1998; Breen et al., 2007; Osborn et. al., 2011; Molofsky et. al., 2011). The critical information derived from the isotopic analysis of dissolved methane is determining the biogenic vs thermogenic source of methane. However, a close review of these previous studies shows an inconsistent consensus on the boundaries of biogenic, thermogenic, and/or mixed origin of methane. The preliminary data collected by my research group in areas of Marcellus Shale drilling in southern Pennsylvania and north central West Virginia demonstrate that high dissolved methane concentrations exists in groundwaters where there is no shale gas drilling activity. We have also collected produced gas samples from Marcellus Shale drilling site in Greene County, PA. Based on C, H isotope signatures and molecular composition it appears that methane in these 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 near-surface fresh waters via acetate fermentation in coal beds and/or beneath landfills and marshes. It is therefore likely that methane from deeper sources is migrating in these groundwater aquifers over millions of years, i.e. geological time scales, through natural structural pathways. However, besides the source; the concentration of stray gas and its molecular and isotopic compositions can be affected by changes in atmospheric conditions, biological processes and physical processes like migration and mixing. The three main objectives of the proposed project are 1) understand the isotopic and molecular composition of natural gas in major coalbed reservoirs in the study area, 2) assess the effect of varying environmental conditions and different sampling methodologies on concentration, isotopic and molecular composition of dissolved natural gas and, 3) understand the relationship between dissolved methane, water quality parameters and stable isotope (C, Oand H) signature of waters. The results from this study will help in development of robust isotopic models to evaluate stray gas incidents in areas of active shale gas drilling.