The effect of synthetic surfactants on the interfacial behaviour of crude oil alkali polymer systems

The effect of synthetic surfactants on the interfacial properties of an alkali/polymer/crude oil system was examined. This system consisted of David Lloydminster crude oil, sodium carbonate (a buffered alkali), either of two synthetic surfactants with high salt tolerance (Neodol 25-3S, an anionic surfactant, or Triton X-100, a nonionic surfactant) and a partially hydrolyzed polyacrylamide (Allied Colloids Alcoflood 1175L). The partitioning of the synthetic surfactant Neodol 25-38 into David Lloydminster crude oil is greatly enhanced by sodium carbonate, Increasing the oil volume fraction in the presence of sodium carbonate enhances the amount of partitioning, the effect of the surfactant depending on the sodium carbonate concentration. Low (0.1 mass%), intermediate (0.2 mass%) and high (0.5-5 mass%) sodium carbonate concentration regions were examined. A linear relationship was observed between interfacial tension (IFT) and t(-1/2), where t is interfacial age, both before and after the minimum IFT was reached. This suggests that the dynamic IFT process is diffusion controlled. With decreasing IFT (before the minimum), the slope of IFT versus t(-1/2) varies linearly with the low-shear Newtonian viscosity of the polymer solutions. This suggests that the rate controlling step of the diffusion process occurs in the aqueous phase. Diffusion was inversely proportional to the square of the low-shear Newtonian viscosity, mu(n)(2), indicating a stronger effect of viscosity on diffusion than predicted by the Stokes-Einstein equation. With increasing IFT (after the minimum), the slope of IFT versus t(-1/2) does not vary linearly with the low-shear Newtonian viscosity of the polymer solutions, suggesting that the rate limiting diffusion process occurs in the oil phase.