Considerations for the Evaluation and Selection of Friction Reducers: Iron Tolerance Assessment Using Residual Polyacrylamide Quantification with Case Study in the Powder River Basin

Abstract Polyacrylamide-based Friction Reducers (FRs) play a crucial role in enhancing hydraulic fracturing efficiency in unconventional reservoirs. Selecting an FR compatible with formation chemistry and operational conditions is essential, particularly as the reuse of high-total dissolved solids (TDS) produced and flowback waters become more common. One of the primary challenges in these high-TDS systems is the presence of ferric iron (Fe+3), which can complex with anionic polyacrylamide (PAM) and form insoluble residues that impair fracture conductivity and formation permeability, Traditional iron stress tests (ISTs) which rely on visual observation or solids mass, provide limited diagnostic value. This study introduces a refined Iron Stress Test (IST) that quantifies both residual PAM and total Fe3+ across solution and solid phases under formation-representative salinity and temperature conditions. The method applies spectrophotometric analysis to determine the distribution of free Fe3+, dissolved PAM, solid-phase iron oxides, and iron-PAM complexes, enabling complete iron mass balance and mechanistic interpretation. Complementary evaluations – including pH, ionic strength, friction flow loop testing – were conducted to correlate iron tolerance with hydraulic performance. Application of this methodology to eight commercial friction reducers (FRs) in synthetic brines (31,000 and 54,000 ppm TDS) representative of Powder River Basin formation waters identified FR-B and FR-C as top performers, retaining > 80% PAM and Fe+3 in solution with minimal precipitation (< 4ppm). The refined IST provides a consistent, quantitative framework for evaluating iron tolerance, revealing how formulation chemistry, salinity, and charge shielding influence polymer stability. By linking laboratory results to subsurface behavior, this approach offers predictive capability for FR performance in iron-rich high-salinity environments, supporting improved chemical selection, reduced formation damage, and enhanced production sustainability.