Friction reducers are essential additives used to economically achieve the high pumping rates required for slickwater fracturing. Decreased friction reducer performance in high-TDS brines has been a major challenge for reusing produced water in hydraulic fracturing. Little work has been done to identify the specific parameters that affect polymeric friction reduction. This research uses friction flow loop experiments to characterize the performance of partially hydrolyzed polyacrylamide friction reducers in conditions relevant to the oil field. Polymer concentration and degree of hydrolysis effects on friction reduction are evaluated in the ranges of 0.25-2 gpt and 0-30%, respectively. The decrease in friction reducer performance is measured in brines up to 120,000 mg/L TDS with varying multivalent cation concentrations. The friction reducer interactions with Na+, Ca2+, Mg2+, Fe3+, and Al 3+ ions are individually assessed. The results are compared to experiments with a commercial friction reducer, and used to propose an empirical model to predict friction reducer performance based on water composition.