Summary The rheological behavior of microemulsion systems was systematically investigated with mixtures of oil, brine, surfactant, cosolvent, and in some cases polymer to determine their effects. A microemulsion-rheology model was developed and used to interpret the experimental results. The optimal microemulsion/oil-viscosity ratio without cosolvent was roughly 5:6, but it can be reduced to a more favorable ratio of approximately 2 by adding cosolvent. Even though the amount of cosolvent needed is case dependent, a clear trend of microemulsion-viscosity reduction with increasing cosolvent concentration was observed. Limited evidence suggests that large hydrolyzed polyacrylamide (HPAM) molecules with a narrow molecular-weight (MW) distribution have negligible partitioning to Type II and Type III microemulsions.

We made measurements of microemulsion rheology with mixtures of oil, brine, surfactant, co-solvent, and in some cases polymer to systematically investigate the effects of salinity, co-solvents and polymers. A microemulsion rheology model was developed and used to interpret the experimental results. We show that the optimum microemulsion-to-oil viscosity ratio is roughly 5 to 6 without co-solvent, but it can be reduced to a more favorable ratio of ~2 by adding co-solvent. Even though the amount of co-solvent needed is case dependent, a clear trend of microemulsion viscosity reduction with increasing co-solvent concentration was observed. Limited evidence suggests that large hydrolyzed polyacrylamide molecules with a narrow molecular weight distribution have negligible partitioning to type II and III microemulsions.