Rheological Properties of Thermoviscosifying Polymers in High-temperature and High-salinity Environments

Thermo-viscosifying polymers (TVPs) are a novel class of materials developed for enhanced oil recovery (EOR) applications in high-temperature and high-salinity (HTHS) oil reservoirs. The rheological properties of the TVP-fluorocarbon surfactant and its interactions with different salts were studied. The effects of surfactant concentration, polymer concentration, salinity, and different inorganic salts on the rheological properties of the TVP and the surfactant-polymer (SP) system were evaluated. Critical association temperature (T-cass) was found to be a function of the TVP concentration and salinity. At low salinity, only thermo-thinning behaviour was observed in the entire temperature range. At high salinity, thermo-thinning was obtained in the low temperature range (<T-cass) followed by thermo-thickening at high temperatures (>T-cass)(.) The interfacial tension between crude oil and the TVP solution was reduced by 3 orders of magnitude with a combination of a fluorocarbon surfactant and a co-surfactant. About a 22 % increase in oil recovery was obtained using the TVP and the SP injection. The TVP showed much better performance and promising results in HTHS conditions compared with commercially available partially hydrolyzed polyacrylamide (HPAM). In HTHS conditions, HPAM suffers a large viscosity loss due to thermo-thinning and charge screening. On the other hand, the high viscosity of the TVP due to thermo-thickening increases oil recovery in HTHS conditions. The thermo-thickening tendency is enhanced by high temperature and high salinity, which makes it more promising for EOR.