Effect of salt and aging on aqueous surfactant formulations for tertiary oil recovery: A correlation of physical properties with microstructure using spin-labels

Physical properties and molecular packing in surfactant aggregates of the surfactant formulation 5% (w/w) TRS 10–410 (a petroleum sulfonate), 3% (w/w) isobutanol and desired quantities of sodium chloride in distilled water were studied using electron spin resonance (ESR) technique and pH, density, viscosity, screen factor, specific conductance, surface tension and free sodium ion measurements of fresh and aged solutions. The results suggested that both salt concentration and aging lead to changes in molecular packing of surfactant aggregates. At optimal salinity, the order parameter was a maximum. With increasing salt concentration, the correlation time increases initially and decreases at higher salt concentration. Various physical property data substantiate the observed microstructural changes. A detailed discussion is presented of the interrelations of these parameters operative in this complex surfactant formulation. Presently with the Whiteshell Nuclear Research Establishment, Atomic Energy of Canada Ltd., Pinawa, Manitoba, Canada ROE 1LO.