Performance of Associative Polymers in the Presence of Low Tension Surfactants at Different Temperatures and Variable Salinity Conditions

Summary Associative polymers (AP) have been shown to develop similar or greater resistance at very low concentrations during polymer transport in comparison to non-associative polymers. This makes AP an attractive option for improved oil recovery at a lower cost. However, their performance dependence on salinity, temperature, concentration, compatibility and interaction with low tension surfactants for improved oil recovery has not been thoroughly understood. The goal of the current work is to study the interaction of these polymers with different surfactant structures and compare their performance with traditional HPAM/AMPS polymers in mobilizing capillary trapped residual oil. We evaluated both HPAM and sulfonated-HPAM based associative polymers with different associative contents in the presence of sulfate and sulfonate surfactants at both moderate and high temperatures with crude oils of different viscosities at high pH and neutral pH conditions. We first tested the effect of the polymers on surfactant - crude oil phase behavior to study the static compatibility and oil solubilization ratios as a function of salinity. Once satisfactory surfactant-crude oil phase behavior results were obtained in the presence of polymer, the next step was injection of single phase surfactant polymer solutions in the absence of oil to observe baseline resistance factors during the propagation of surfactant-polymer slug in the surrogate rock. Finally, we evaluated the performance of these associative polymers during the displacement of residual oil. We compared the recovery performance of the associative polymers with conventional polymers in terms of remaining oil saturation, oil bank propagation and pressure gradients during the surfactant-polymer flooding process. Results indicate that associative polymers are generally compatible with traditional low tension surfactants as seen from the phase behavior experiments and corefloods. The associative polymers are aqueous stable at optimal salinity and show no plugging in single phase injectivity experiments in Bentheimer sandstone. The associative polymers show comparable oil recovery to conventional HPAM and sulfonated HPAMs at a lower polymer dosage and appear to be good alternatives for field application. Based on the laboratory results, we demonstrate that associative polymers can be used with low-tension surfactants for EOR at lower concentrations.