Abstract:

To solve the problem that the high cost of microemulsion has limited the field application, in this work, the single-phase microemulsion was diluted to construct a diluted microemulsion system. The heavy oil from CF oilfield in Xinjiang was taken as the object to explore the synergistic mechanism of enhanced oil recovery by using a solvent n-tetradecane （n-C₁₄） and a surfactant （cationic CTAB, anionic SDS or nonionic OP-10）.A stable single-phase microemulsion formulation with the mass ratio of active substance to solvent of 8∶2 was determined by titration, and it was diluted to a surfactant mass fraction of 0.25% to form a diluted-microemulsion system. The performance characterization showed that the micelle size of the system was nanoscale, and the system was relatively stable. The mechanism research showed that: 1） Diluted-microemulsion could significantly reduce the oil-water interfacial tension and weaken the capillary force to drive the flow of residual oil; 2） Static experiments showed that the solvent was released into crude oil with the aid of surfactant, which reduced the viscosity of crude oil and promoted the formation of oil-in-water emulsion; 3） The surfactant could regulate the wettability of rock, reduce the adhesion of crude oil and improve the permeability of water phase. The mechanism of wettability change varied depending on the type of surfactant and the charge of rock surface: CTAB was able to desorb the acidic groups of crude oil from the surface of sandstone in an irreversible way by forming ion pairs, while SDS and OP-10 relied on another action mechanism. Among them, CTAB showed the best performance in wettability modification. Based on the synergistic mechanism above, the diluted microemulsion effectively improved the heavy oil recovery. This work might provide theoretical basis and technical support for the application of diluted microemulsion in heavy oil recovery.

Key words: diluted-microemulsion, heavy oil, enhanced oil recovery, solvent, surfactant