The geochemistry of hydraulic fracturing fluids

The inorganic geochemistry of hydraulic fracturing fluids is reviewed with new insights on the role of entrapped formation waters in unconventional shale gas and tight sand formations on the quality of flowback and produced waters that are extracted with hydrocarbons. The rapid increase of the salinity of flowback fluids during production, combined with geochemical and isotopic changes, indicate mixing of the highly saline formation water with the injected water. The salinity increase suggests that the volume of the injected water that is returned to the surface with the flowback water is much smaller than previous estimates, and thus the majority of the injected water is retained within the shale formations. The high salinity of the flowback and produced water is associated with high concentrations of halides, ammonium, metals, metalloids, and radium nuclides that pose environmental and human health risks upon the release of the hydraulic fracturing fluids to the environment. (C) 2017 The Authors. Published by Elsevier