Syntheses and properties of associative acrylamide copolymers containing short hydrophobic chains used in a friction reducer for slick-water fracturing

Two allyldimethylalkyl quaternary ammonium salt (AQAS) monomers, N,N-dimethylallylphenylpropylammonium bromide (AQAS1) and N,N-dimethylallylnonylammonium bromide (AQAS2), were synthesized and used to prepare modified polyacrylamide materials. Two new drag reducers were synthesized from acrylamide (AM), sodium acrylate (NaAA) and a cationic modified monomer (AQAS1 or AQAS2) via aqueous solution polymerization, and the copolymers were named P(AM/NaAA/AQAS1) and P(AM/NaAA/AQAS2), respectively. The structures of the drag reduction agents were confirmed by IR and ¹H NMR spectroscopies. The molecular weight (M_w) of P(AM/NaAA/AQAS1) was 1.79 × 10⁶ g/mol. When the copolymer concentration was 1000 mg/L and the flow rate was 45 L/min, in fresh water the highest drag reduction rate was 75.8%, in 10,000 mg/L NaCl solution the drag reduction rate decreased to 72.9%. The molecular weight of P(AM/NaAA/AQAS2) was 3.17 × 10⁶ g/mol. When the copolymer concentration was 500 mg/L and the flow rate was 45 L/min, the drag reduction rate reached 75.2%, and in 10,000 mg/L NaCl solution the drag reduction rate was 73.3%, decreased by approximately 1.9%. The drag reduction rate for partially hydrolyzed polyacrylamide (HPAM) was also investigated, and the results showed that the drag reduction rates for 500 and 1000 mg/L HPAM solutions were merely 43.2% and 49.0% in brine, respectively. Compared with HPAM, both of the above copolymers presented better drag reduction capacities.