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 electric fields as investigated by means of time-domain dielectric spectroscopy (TDS) is reported. The studied emulsions include true crude-oil-based ones as well as model systems stabilised by indigenous crude oil fractions or, alternatively, by commercial nonionic surfactants. It is seen that the developed TDS equipment gives a good quantitative measure of the emulsion stability. The emulsion stability in crude oil systems can be modelled by the separated asphaltene fraction as far as coalescence is considered. Although the resin fraction might be even more interfacially active than the asphaltenes, it cannot alone stabilise the w/o emulsions. The importance of the interplay between the asphaltenes and resins is clearly revealed. When commercial surfactants (ethoxylated nonyl phenols, NP-EO or monoalkyl sorbitan esters) are combined with the separated crude oil fractions, different levels of compatibility are displayed. The addition of a tetraoxyethylene nonyl phenol ether (NP-4), for instance, completely destabilises the original emulsion, although a high level of interfacial activity is retained in the system.