Geochemical and isotope analysis of produced water from the Utica/Point Pleasant Shale, Appalachian Basin

Abstract

While development of the Utica/Point Pleasant Shale (UPP) is extensive in Ohio (U.S.) and increasing in Pennsylvania and West Virginia, few studies report the chemistry of produced waters from UPP wells. These data have important implications for developing best management practices for handling and waste disposal, or identifying the fluid in the event of accidental spill events. Here, we evaluated the elemental and isotope chemistry of UPP produced waters from 26 wells throughout Ohio, Pennsylvania, and West Virginia to determine any unique fluid chemistries that could be used for forensic studies. Compared to the Marcellus, UPP produced waters contain higher activities of total radium (²²⁶Ra + ²²⁸Ra) and higher ²²⁸Ra/²²⁶Ra ratios. As with the Marcellus Shale, elemental ratios (Sr/Ca) and isotope ratios (⁸⁷Sr/⁸⁶Sr) can distinguish UPP produced waters from many conventional oil and gas formations. Sr/Ca and ⁸⁷Sr/⁸⁶Sr ratios can fingerprint small fractions (∼0.1%) of UPP produced water in freshwater. However, because Marcellus and UPP produced waters display similar major elemental chemistry (i.e., Na, Ca, and Cl) and overlapping ratios of Sr/Ca and ⁸⁷Sr/⁸⁶Sr, ²²⁸Ra/²²⁶Ra ratios may be the best tracer to distinguish these waters.