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-2acrylamido-tertbutylsulfonic acid (ATBS) terpolymer in the presence of varying initial levels of dissolved oxygen (0 to 8,000 ppb), Fe2þ (0 to 220 ppm), and Fe3þ (0 to 172 ppm). A special method was developed to attain and confirm dissolved-oxygen levels. Stability studies were performed at 23 and 90 C. For Fe2þ 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 C with only 10-ppb initial dissolved oxygen, contact with steel caused HPAM-ATBS solution viscosity losses greater than 30%. In contrast at 23 C, contact with steel caused no significant degradation when the dissolved O2 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 Fe3þ to polymer solutions caused immediate crosslinking. Because crosslinked polymers were never observed during our studies with Fe2þ, we conclude that free Fe3þ was not generated in sufficient quantities to form a visible gel.