Summary
In this study, an oil-in-water nanoemulsion for the effective removal of an oil-based drilling fluid has been developed by means of the phase-inversion concentration method. The influence of four factors on the droplet size and removal efficiency were tested, including the mass ratio of mixed surfactants (Rm), the surfactant/oil ratio (SOR), the mass concentration of cosurfactant (cco), and the salinity of the saline solution (cs). Considering the application environment of displacement spacers, the long-term stability and temperature resistance were investigated. The results showed that Rm and SOR had an obvious influence on the removal efficiency and droplet size of nanoemulsions. Because of the synergy effect of the surfactants, the nanoemulsion possesses remarkable storage stability and temperature resistance. Moreover, the removal mechanisms of the nanoemulsion were analyzed by the dynamic interfacial tension (IFT), dynamic wetting angle, and solubilization tests. The results indicated that the nanoemulsion could spread rapidly and thoroughly on the oil-wetting surfaces, and the nanoemulsion can contain more oil while the system is still stable, which is beneficial for the removal of an oil-based drilling fluid.
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