Surfactant molecules are tested as water-in-crude emulsion breakers to attain the quickest separation rate in the so-called “proportional regime”. A concept of demulsifier performance is proposed on the basis of the required demulsifier concentration to offset the effect of a given amount of asphaltenes. The experimental evidence allows one to rank the tested products and relate their performance to their hydrophilicity and molecular weight. Some evidence indicates that the presence of acids in the crude makes it easier to break emulsions and suggests that so-called “extended surfactants” can significantly shorten the demulsifying process.

Hydrophilic surfactant molecules with the proper formulation are able to break W/O emulsions stabilized by asphaltenes and other lipophilic amphiphiles as found in the effluent of petroleum wells. The demulsifier performance is here tested according to two critera. The first one, as in previous research, is the minimum dose of demulsifier used to attain the minimum stability at the so-called optimum formulation in a simplified bottle test. The second criterion is the value of this minimum stability at optimum formulation that has a direct relation with the separation time. Our findings show that in a family of ethoxylated surfactants, the best demulsifier is a hydrophilic one, though not too much. When the demulsifier is a mixture of two surfactants, it usually exhibits an intermediate behavior between the components. However, the mixture sometimes appears to be better than any of the components alone with some synergistic effect that improves the performance.

The performance of several extended surfactants as water-in-crude oil emulsion breakers was evaluated using two criteria: (1) the demulsifier dose required (C D*) to attain the minimum stability at the so-called optimum formulation, and (2) the corresponding low minimum stability value. These surfactants were found to behave in the same way as typical commercial demulsifiers do; i.e., they require a lower dose C D* when their hydrophilicity is slightly greater. The reported data for a dozen different extended surfactants indicate how the two performance indices are altered by changing the structure characteristics, such as the propylene oxide number, the ethylene oxide number, and the ionic polar group (carboxylate, sulfate, phosphate). The best performance as a demulsifier seems to depend on the proper combination of these structures to attain a well-fitting compromise.

Stable water-in-oil emulsions with water volume fraction ranging from 10 to 70 vol % have been developed with mineral oil 70T, Span 80, sodium di-2-ethylhexylsulfosuccinate (AOT), and water. The mean size of the water droplets ranges from 2 to 3 μm. Tests conducted show that all emulsions are stable against coalescence for at least 1 week at 2 °C and room temperature. Furthermore, it was observed that the viscosity of the emulsion increases with increasing water volume fraction, with shear thinning behavior observed above certain water volume fraction emulsions (30 vol % at room temperature and 20 vol % at 1 °C). Viscosity tests performed at different times after emulsion preparation confirm that the emulsions are stable for 1 week. Differential scanning calorimetry performed on the emulsions shows that, for low water volume fraction emulsions (<50 vol %), the emulsions are stable upon ice and hydrate formation. Micromechanical force (MMF) measurements show that the presence of the surfactant mixture has little to no effect on the cohesion force between cyclopentane hydrate particles, although a change in the morphology of the particle was observed when the surfactant mixture was added into the system. High-pressure autoclave experiments conducted on the model emulsion resulted in a loose hydrate slurry when the surfactant mixture was present in the system. Tests performed in this study show that the proposed model emulsion is stable, having similar characteristics to those observed in crude oil emulsions, and may be suitable for other hydrate studies.