STABLE ISOTOPE FINGERPRINTING OF CO-PRODUCED WATERS ASSOCIATED WITH MARCELLUS SHALE NATURAL GAS EXTRACTION

The main concern associated with Marcellus shale gas development is that water co-produced as a result of hydraulic fracking can potentially compromise the water quality of surface waters and fresh water aquifers of the region. In order to assess the effect of Marcellus shale development on water quality, there is a need to develop tools that can be used to track the source and fate of these highly saline waters co-produced as a result of shale gas extraction. In the area of Marcellus shale development, the co-produced water can have similar chemical constituents found in saline formations and/or coal mines originating from several thousand acres of abandoned coal mines or deep coal mines in this region. Hence, it can be difficult to decouple the contribution of co-produced water from coal mine waters and/or saline formation waters to the surface waters and aquifers based on the general geochemical characteristics alone. We tested the applicability of a multiple stable isotope approach to distinguish different water sources in an area of accelerating shale gas development. Water samples were collected from fresh surface waters, coal mine discharges and co-produced water from a Marcellus well in Pennysylvania. Preliminary data shows that O and H isotopic composition of water (δ¹⁸O_H2O and δD_H2O), C isotope composition dissolved inorganic carbon (δ¹³C_DIC), and S and O isotope composition of dissolved sulfate (δ³⁴S_SO4 and δ¹⁸O_SO4) of different end-members are very distinct. The isotopic variations most likely originate due to the variations in water-rock interactions, recharge sources, recharge pathways, and age of the waters. These distinctions may be used to fingerprint different water sources in this area.