Synthesis and rheological properties of water soluble ionic copolymers as modifier fluids at high temperature and saline media

Abstract

Polymer flooding depicts an interesting strategy to improve the enhanced oil recovery (EOR). This work aims with the synthesis of ionic thermo‐responsive copolymers able to be used as rheological modifiers for EOR under harsh conditions (250,000 ppm of NaCl at 150°C). Copolymers composed of different molar ratio of acrylamide, N‐isopropylacrylamide and 2‐acrylamide‐2‐methyl‐1‐propanesulfonic acid were prepared in aqueous media via free radical polymerization at 50°C using 4,4′‐azobis(‐4″‐cyanopentanoic) acid (ACPA) as initiator. Nuclear magnetic resonance analyses demonstrated the structure and molar composition of synthesized copolymers. Rheological measurements performed at different concentration from 1 to 8 wt% demonstrated an increase in the viscosity from 2000 to 600,000 mPa.s. Aqueous mixtures of polymer at 5 wt% and NaCl at different concentration (5, 10, 15, 20, and 25 wt%) was analyzed. Copolymer ([PAM]/[PNIPAM] = 50/50) displayed a phase separation at 15 wt% of NaCl. Solutions of polymer at 5 and 25 wt% of NaCl were heated at 150°C for 72 h. Results revealed both thermal stability and saline tolerance of copolymers [PAM]/[PNIPAM]/[PAMPS‐Na] = 25/25/50, 35/35/30, and 50/0/50 under harsh conditions with the absence of phase separation of the brine polymer solutions.