CRUDE-OIL EMULSIONS IN HIGH ELECTRIC-FIELDS AS STUDIED BY DIELECTRIC-SPECTROSCOPY - INFLUENCE OF INTERACTION BETWEEN COMMERCIAL AND INDIGENOUS SURFACTANTS

The behaviour of different types of water-in-oil emulsions in high ele ctric fields as investigated by means of time-domain dielectric spectr oscopy (TDS) is reported. The studied emulsions include true crude-oil -based ones as well as model systems stabilised by indigenous crude oi l fractions or, alternatively, by commercial nonionic surfactants. It is seen that the developed TDS equipment gives a good quantitative mea sure of the emulsion stability. The emulsion stability in crude oil sy stems can be modelled by the separated asphaltene fraction as far as c oalescence is considered. Although the resin fraction might be even mo re interfacially active than the asphaltenes, it cannot alone stabilis e the w/o emulsions. The importance of the interplay between the aspha ltenes and resins is clearly revealed. When commercial surfactants (et hoxylated nonyl phenols, NP-EO or monoalkyl sorbitan esters) are combi ned with the separated crude oil fractions, different levels of compat ibility are displayed. The addition of a tetraoxyethylene nonyl phenol ether (NP-4), for instance, completely destabilises the original emul sion, although a high level of interfacial activity is retained in the system.