Effect of Dissolved Iron and Oxygen on Stability of Hydrolyzed Polyacrylamide Polymers

This paper describes an experimental study of the stability of a hydrolyzed polyacrylamide (HPAM) polymer and an HPAM-2-acrylamido-tertbutylsulfonic acid (ATBS) terpolymer in the presence of varying initial levels of dissolved oxygen (0 to 8,000 ppb), Fe2+ (0 to 220 ppm), and Fe3+ (0 to 172 ppm). A special method was developed to attain and confirm dissolved-oxygen levels. Stability studies were performed at 23 and 90 degrees C. For Fe2+ concentrations between 0 and 30 ppm, viscosity losses were insignificant after 1 week when the initial dissolved oxygen concentration was 200 ppb or less. Above this level, significant viscosity losses were seen, especially if iron was present. If the temperature is high, a greater need arises to strive for very low dissolved-oxygen content. For samples stored for 1 week at 90 degrees C with only 10-ppb initial dissolved oxygen, contact with steel caused HPAM-ATBS solution viscosity losses greater than 30%. In contrast at 23 degrees C, contact with steel caused no significant degradation when the dissolved O-2 concentration was 1,000 ppb or less. Several different methods are discussed to control oxidative degradation of polymers during field applications. We advocate physical means of excluding oxygen (e.g., stopping leaks, better design of fluid transfer, gas-blanketing, gas-stripping) rather than chemical means. Addition of Fe3+ to polymer solutions caused immediate crosslinking. Because crosslinked polymers were never observed during our studies with Fe2+, we conclude that free Fe3+ was not generated in sufficient quantities to form a visible gel.