Isotopic Fingerprints for Delineating the Environmental Effects of Hydraulic Fracturing Fluids

Unconventional shale gas and tight sand exploration through hydraulic fracturing accounts for a large fraction of oil and gas production in the US and will soon be launched on a global scale. One of the complexities in evaluating the environmental impact of hydraulic fracturing and shale gas development is the legacy of conventional oil and gas exploration in the same areas. Data from the USGS produced water database coupled with new data generated from flowback and produced waters from several basins in the US reveal that the formation water is typically hypersaline and characterized by a Ca-chloride composition with high Br/Cl ratios that reflect different degrees of seawater evaporation and water-rock interactions. In many cases, the chemistry of effluents from unconventional and conventional wells is indistinguishable. In the Appalachian Basin, flowback from the Marcellus Shale has distinctive trace element (B/Cl, Li/Cl) and isotopic (87Sr/86Sr, δ11B, δ7Li, 228Ra/226Ra) fingerprints that are different from those in produced waters from conventional oil and gas wells. The integration of these geochemical and isotopic tracers could provide robust monitoring tools for evaluating the environmental effects and delineating the specific impact of unconventional oil and gas operations.