Breaking of Water-in-Crude-Oil Emulsions. 3. Influence of Salinity and Water−Oil Ratio on Demulsifier Action

The stability of water-in-diluted-crude-oil emulsions is found to depend upon the water-phase salinity and the water−oil ratio for different asphaltene and demulsifier concentrations. It is reported that the most stable emulsions are formed when one of the phase volumes largely exceeds the other and that the minimum stability is found at the formulation for which the emulsion inversion takes place. For asphaltene concentrations over 500 ppm, this occurs at a volumetric fraction between 0.3 and 0.7 and, in this range, the higher the water-phase content, the lower the required demulsifier concentration. It is also determined that there is an optimum value of the demulsifier concentration that promotes the fastest separation. At a fixed asphaltene concentration, an increase in salinity generally leads to a lower demulsifier requirement. Finally, at higher asphaltene concentrations, simultaneous increases in salinity and demulsifier concentration are required to attain an optimal rate of emulsion breaking.