A Study of Polymer/Surfactant Interactions for Micellar/Polymer Flooding Applications

Static measurements of the phase volumes of mixtures of surfactant, polymer, alcohol, water, n-octane, sodium chloride, and in some cases polymer additives were made. A limited number of viscosity, phase concentration, and IFT measurements were also made. The purpose was to systematically determine the affect of various polymers on the phase behavior of various surfactant formula-tions. Measurements with and without oil (n-octane) were made across a range of salinity appropriate to the particular surfactant at temperatures between 24 and 75° C. The polymers used were xanthan gum, hydrolyzed polyacrylamide, polyacrylamide, hydroxyethylcellulose, and polyethyleneoxide of three different molecular weights. The surfactants used were Exxon's C 12 MEAOXS, Witco's TRS 10-80, Stepan's Petrostep 465, Alcolac's Siponate DS-10, GAF's Igepal C0-530 and C0-610, and Witco's ethoxylated alcohol TDA-100. The alcohols were isobutyl, secondary butyl, isopentanol, and isopropanol. The oil free (i.e. no added oil) solutions showed a characteristic phase seperation into an aqueous surfactant rich phase and an aqueous polymer rich phase, at some sufficiently high salinity (NaCl concentration), which we call the CEC. The CEC was found to be a characteristic 6f a given surfactant/alcohol combination, which shifts with the solubility of the surfactant, qualitatively the ., same way as the optimal salinity does. But the CEC was found to be independent of the polymer type, polymer concentration (between the 100 and 1000 ppm limits investigated), and surfactant concentration. The CEC increases with temperature for the anionic surfactants and decreases with temperature for the nonionic surfactants. When oil was added to the above mixtures an entirely different pattern of phase behavior was observed. The particular formulations form the typical sequence of lower phase microemulsion and excess oil; middle phase microemulsion, excess oil, and excess brine; and upper phase microemulsions and excess brine; as salinity increases. The sequence with polymer was precisely the same over most of the salinity range but deviated over a limited range of salinity: the three phase region simply shifts a small distance to the left on the salinity scale. Also, and probably more significantly, some of the "aqueous" phases in the critical region of the shift (which is also just above oil-free CEC salinity) were found to be gel-like in nature. These apparently occur under conditions such that the polymer concentration in the excess brine of the three phase systems becomes very high, due to the fact that almost all the polymer is always in the brine phase, even when the brine phase is very small. Thus an overall 1000 ppm of polymer can easily be concentrated to 10000 ppm or more. One of the most remarkable aspects of the phase behavior of the surfactant/polymer systems is that the same patterns are observed for all combinations of anionic and nonionic surfactants and polymers. Also, little difference was observed in the IFT values with and without polymer. The three phase systems still exhibited ultra-low IFT values. Obviously, significant differences did occur in the brine viscosities when polymer was added. The polymer free mixtures were themselves quite viscous, however; and the viscosity of the oil free surfactant rich phases (above the CEC) were significantly higher when in equilibrium with a polymer rich aqueous phase, even though apparently containing almost no polymer. The polymer rich phases had normal viscosities as judged by the same polymer in the same brine at the expected concentration assuming all of the polymer was in the polymer rich phase. The affect of polymer on the systems with oil was to increase the viscosity of the water rich phase only, with little effect on the microemulsion phase unless it was the water rich phase.