Thermothickening and Salinity Tolerant Hydrophobically Modified Polyacrylamides for Polymer Flooding

Partially hydrolyzed polyacrylamide (HPAM) is by far the most used synthetic polymer in enhanced oil recovery (EOR) projects. Shortcomings of HPAM include a highly molecular weight ( M w ) dependent viscosity yield and decreasing viscosifying ability with increasing salinity and temperature. For an economically viable project, this limits its use to reservoirs with low to moderate salinities and temperatures. In that respect, hydrophobically modified polyacrylamides (HMPAM) has been suggested as an alternative for applications at higher salinities and temperatures. While studies have compared the performance of modified versus unmodified commercial EOR polymers at different salinities and temperatures, and the structure–property relationship of monodisperse, low M w HMPAM, published data on the simultaneous effect of polymer hydrophobicity, salinity, and temperature for commercial EOR polymers are limited. This study thus presents a comprehensive series of experiments to investigate the effect of polymer hydrophobicity on viscosifying ability as a function of salinity and temperature. The main findings of these experiments are that the balance between salinity effects and thermal behavior shifts the order of viscosifying ability so that the polymer with the best viscosifying abilities at low temperatures and salinities is outperformed at conditions of high salinity and temperature. This highlights the importance of structure–activity studies at relevant reservoir conditions prior to selection of a solution for field application.