Preparation and properties of a hydrophobically associating friction reducer for fracturing in low-permeability gas reservoirs.

Fracturing operations in low-permeability gas reservoirs impose stringent requirements on the temperature, salt, and shear resistance of friction reducers. Although hydrophobic group structures critically determine these properties, the underlying mechanisms remain poorly understood. This study designed and synthesized two cationic hydrophobic monomers: a rigid monomer containing a benzene ring (AQB) and a flexible monomer featuring a branched alkyl chain (AQL). Through aqueous free-radical polymerization, these were copolymerized with acrylamide and sodium acrylate to prepare rigid (PB) and flexible (PL) hydrophobically associating friction reducers. The polymer structures were characterized using infrared spectroscopy, followed by a systematic comparison of their solubility, rheological behavior, friction reduction efficiency, and salt tolerance. The results indicate that the critical association concentration of PB is 1800 mg/L, lower than that of PL (2500 mg/L), suggesting that the rigid benzene ring facilitates the formation of an intermolecular association network. Rheological evaluations reveal that PB exhibits a viscosity retention rate of 71% at 90 °C and 88% after continuous shearing for 3600 s, both outperforming those of PL (58% and 79%, respectively). Scanning electron microscopy observations confirm that PB constructs a more compact and dense three-dimensional network. Furthermore, performance assessments demonstrate that 1000 mg/L of PB achieves friction reduction rates of 76.2% in fresh water, 71.8% in 20,000 mg/L NaCl brine, and 62.1% in 5000 mg/L CaCl