Effect of the Fluid–Shale Interaction on Salinity: Implications for High-Salinity Flowback Water during Hydraulic Fracturing in Shales

Abstract

Hydraulic fracturing has been widely implemented to enhance hydrocarbon production from shale reservoirs. However, one of the main challenges during hydraulic fracturing is to understand what factor(s) triggers high salinity of flowback water, which sometimes can be up to 300,000 mg/L. While several mechanisms have been proposed to explain the controlling factor behind the high salinity of flowback water, there has been little discussion about the effect of fluid-shale interactions (e.g., mineral dissolution and surface complexation) on the high salinity, and far too attention has been paid to quantify the contribution of fluid-shale interactions. We thus conducted spontaneous imbibition experiments using deionised water and outcrops from Marcellus, Barnett and Eagle Ford shale plays with minor in-situ precipitated salts. We also monitored the pH, electrical conductivity and ion concentrations (Cl-, K+, Ca2+, NO3-, F-, Br- and NH+) of the surrounding water during spontaneous imbibition process in consecut...