Impact of water-rock interactions on indicators of hydraulic fracturing flowback fluids produced from the Jurassic shale of Qaidam Basin, NW China

Abstract Water-rock interactions occurring during fracturing and flowback in shale gas reservoirs may dominate some chemical and isotopic compositions of hydraulic fracturing flowback fluids (HFFF) by imparting characteristic compositions of the continental shale to the HFFF. In this paper, a simple conservative mixing model (SCMM) and a progressive conservative mixing model (PCMM) were developed to evaluate and understand the impacts of geochemical processes on forensic indicators (δ11B, 87Sr/86Sr, and Ba/Sr) of HFFF produced from the Dameigou Shale. Application of the paired sample T-test showed that the measured values of δ11B, 87Sr/86Sr, Ba, and Sr in HFFF produced from the Dameigou Shale were all significantly (p  1.45) in HFFF. Therefore, 87Sr/86Sr and Ba/Sr show potential as indicators of continental HFFF produced from carbonate-poor shales and provide a clear distinction from rapidly-circulating shallow groundwater mainly recharged by rainwater (87Sr/86Sr: 0.70903–0.70914 and Ba/Sr: