Separation of Oil and Water Emulsions: Is Heating Good Enough?

Abstract

Abstract Surfactants and nanoparticles (NP) frequently act as stabilizers for oil and water emulsions. There is a need to investigate whether such NP stabilized emulsions (also known as Pickering emulsions) require different treatment for break-up, as compared to the well-known method to separate surfactant stabilized emulsions, i.e., heating. Thus, the main objectives of this work were to identify emulsions resistant to heating and develop a process able to accelerate the separation kinetics of such ultra-tight emulsions. Extensive experimental investigations on the stability of different types of oil and water emulsions under various temperature and brine salinity conditions were carried out using a state-of-the-art Portable Dispersion Characterization Rig (P-DCR). The batch separator was equipped with a high-resolution, surveillance camera to monitor emulsion separation kinetics. Commercial grade mineral oil and synthesized brines with various salinities were used as the test fluids. Silica nanoparticles of different wettability and surfactants with different HLB values were deployed as the stabilizing agents for the produced emulsions. It was found that the elevated temperature effects dominate the separation kinetics of the studied emulsions, as compared to any brine salinity effects, especially at higher temperatures, namely, 60°C and 80°C. Moreover, the effects of high temperatures and brine salinities on the separation kinetics were much more significant for the emulsions stabilized by surfactants than for NP stabilized emulsions. Perhaps more importantly, neither high temperature nor high brine salinity had any remarkable effects on the separation kinetics of the emulsions stabilized by hydrophobic NP. It was also shown that the hydrophobic NP dominate the stability mechanism for dual emulsifier fluid systems, such as emulsions stabilized by both hydrophobic NP (R974) and a surfactant of low HLB value (Span 80). A novel oil-water emulsion break-up process was developed to enhance the kinetics of the separation, irrespective of the underlying emulsion stability mechanisms, namely, surfactant, NP or both. The performance of this separation process was superior to heating, which is the conventional method applied to separate oil-field emulsions. Finally, it is envisioned that the newly developed process may be applied in the field as an in-line separation system for tight oil-field emulsions.