The Effect of Temperature on Gelation Time for Polyacrylamide/Chromium (III) Systems

Gelled polymers are being applied to modify the movement of injected fluids in the vicinity of injection and production wells in secondary and enhanced oil-recovery projects. One approach to gelation is to form a bulk gel in situ by injecting a slug of a polyacrylamide polymer solution containing chromium(VI) followed by a polymer slug containing a reducing agent such as sodium bisulfite. Upon mixing, CR(VI) is reduced to Cr(III), and in the subsequent reaction a gel is formed. The gelation time controls the volume of fluid that can be injected in the treatment and thus is an important variable in the process. Gelation time is known to be a function of the concentration of the reactants (chromium ion, reducing agent, and polymer) as well as the polymer type, and some data relating these variables to gelation time have been reported. Another variable affecting the reaction rate is temperature, but no data relating gelation time and temperature have been published. The purposes of the work described in this paper were to obtain experimental data on the effect of temperature on gelation time for typical polyacrylamide/Cr(III) gel systems over the range of temperatures commonly encountered in reservoirs and to develop a methodmore » of correlating the data. Gelation times were measured for five different polymers, including polymers with various degrees of hydrolysis and polymers with nonionic, anionic, and cationic character. The temperature range was 25 to 80/sup 0/C. Polymer, metal ion, and redox system concentrations and salinity also were varied. It was determined that, for a given polymer-reducing agent system at a specified concentration, the gelation time decreases as temperature is increased. The data were correlated in a manner analogous to the Arrhenius method of correlating chemical reaction rate data.« less