Thermosensitive water soluble polymers: A solution to high temperature and high salinity reservoirs

Partially hydrolyzed polyacrylamide (HPAM) is one of the most widely reported polymers for chemical enhanced recovery (EOR) since most of the previous work deals with low-temperature and low-salinity reservoirs. As most of the remaining oil is in the deeper and hotter reservoirs, application of HPAM is limited because it is not suitable for high-temperature and high-salinity (HTHS) conditions. HPAM suffer a huge viscosity loss due to charge shielding effect and hydrolysis of the amide group. In presence of divalent cations, hydrolyzed product may also precipitate. In this work, we propose a novel thermo-sensitive water soluble polymer for HTHS conditions. Due to the presence of thermo-sensitive monomer, as the temperature exceeds lower critical solution temperature (LCST), the formation of physical network takes place. This formation of physical network results in the viscosity enhancement. The rheological behavior of the polymer was investigated using Discovery Hybrid Rheometer (DHR-3) at different polymer concentrations, temperatures, and in presence of different ions. Two different regions were observed in the viscosity-temperature plot. At lower temperatures (T< LCST), thermo-thinning behavior was observed i.e. viscosity decreased with temperature. At higher temperatures (T> LCST), the thermo-thickening behavior was observed i.e. the viscosity increased with temperature. This thermo-thickening also depends on the salinity of the solution. By increasing the salinity of the solution, the LCST shifted at low temperatures. In deionized water, no thermo-thickening was observed and only thermo-thinning behavior was noted. Such type of viscosity behavior is highly desirable for EOR operation as low viscosity at low temperatures ease the pumping operation. As the liquid move down the reservoir, the solution viscosity increases due to the formation of network structure.