DYNAMIC INTERFACIAL-TENSION OF CRUDE-OIL ALKALI SURFACTANT SYSTEMS

An experimental study was conducted to examine the dynamic interfacial tension in crude oil/alkali/surfactant systems over a wide range of parameters. The system examined contained David Lloydminster crude oil, sodium carbonate (a buffered alkali) and one of two synthetic surfactants with high salt tolerance (Neodol 25-3S or Triton X-100). Crude oil/alkali systems showed a minimum interfacial tension (IFT) of 0.02 mN m-1 at an optimum alkali concentration of 0.2 mass%. The effect of the synthetic surfactant depended on the alkali concentration: at alkali concentrations of less than 0.2 mass%, the synthetic surfactant generally yielded minimum IFT values greater than 0.2 mN m-1, except at very low surfactant concentrations (about 0.001 mass%) where IFT values as low as 0.02 mN m-1 were obtained; at an alkali concentration of 0.2 mass%, the addition of synthetic surfactant raised the minimum IFT; and at alkali concentrations greater than 0.2 mass%, the addition of synthetic surfactant produced minimum IFT values of 0.02 mN m-1 at surfactant concentrations that varied from 0.001 to 0.5 mass%. It was also found that the dynamic IFT behaviour of crude oil/alkali/surfactant systems having the same ionic strength was quite similar. In these systems, some of the sodium carbonate was replaced with sodium chloride to produce an aqueous phase of the same ionic strength and nearly the same pH. The time required to reach the minimum IFT was found to be a function of the alkali/surfactant mass ratio. The minimum time required to reach an IFT minimum was 2 min at alkali/surfactant mass ratios of 0.1-10. At higher ratios, the time required to reach minimum IFT increased. The results obtained from the present study showed that the addition of a synthetic surfactant with high salt tolerance to crude oil/alkali systems did not always lower the IFT, and consequently care should be taken when formulating such systems for enhanced recovery purposes.