The dielectric properties and the composition of fourteen light to heavy crude oils have been analyzed. Frequency domain spectroscopy (FDS) has been used in order to determine their dielectric response in the frequency range 0.01 to 1000 Hz. For all the crude oils, over the whole frequency range under study, dielectric loss, ϵ″, shows a linear dependence of frequency indicating a pure direct current (DC) conductivity. As temperature is gradually increased, the dielectric loss, ϵ″, increases as well, showing a strong temperature dependence. The storage modulus, ϵ′, shows an explicit behaviour at low frequency that could be due to adsorption of oil components onto the electrodes. We tried to correlate some physical and chemical properties (density, viscosity, SARA, TAN, water content) of the studied crude oils with their conductivity measured at various temperatures. No correlation was found and different hypothesis are suggested by the authors to explain this phenomenon.

Dielectric properties and viscosities of two different crude oils (labelled E and N) and solutions of them diluted in toluene or heptane were measured by frequency domain spectroscopy and rheology, respectively. Crude oils E and N diluted with toluene show a linear trend when plotting conductivity as a function of 1/viscosity. The crude oils diluted with the same amount of heptane show a lower conductivity than those in toluene. These results indicate that the conductivity of crude oil solutions is governed by the aggregation state of the asphaltenes more than their quantity in the crude, since asphaltenes are known to be in a more aggregated state in heptane than in toluene. In order to vary the viscosity while keeping the asphaltene concentration and solvation status constant, conductivity measurements of both crude oils diluted with solutions of polystyrene in toluene were performed. For the results obtained for the polystyrene modified systems, the proportionality between conductivity and 1/viscosity is not valid for low viscosities.

The dielectric properties of asphaltenes precipitated from four different crude oils have been Studied ill the frequency range of 0.01-1000 Hz by frequency domain spectroscopy (FDS). The asphaltenes were dissolved in toluene, and the dielectric response of the solutions was measured at different concentrations. To determine the precipitation point, titrations of the toluene solutions with heptane were performed and monitored by near-infrared spectroscopy. The dielectric properties of the asphaltenes were then also examined close to and well above the precipitation point,