Influence of Wax Precipitation on the Impedance Spectroscopy of Waxy Oils

Impedance spectroscopy (IS) is a widely used nondestructive and high-throughput experimental technique for the characterization of electrical properties of materials. In the petroleum industry, IS is frequently employed to determine the electrical properties of asphaltenes and resins. The electrical properties of waxy crude oils, which correlate significantly with the flowability, however, have received little to no attention in the existing investigations. In this work, we inspected the influence of wax precipitation on IS of waxy crude oil for the first time. The investigation was carried out in a frequency range of 2 X 10(-1) to 2 X 10(4) Hz and a temperature range of 5-60 degrees C. It was discovered that the Nyquist diagram representing the electrical response of waxy oil evolves from one semicircle to two semicircles as wax molecules precipitate at temperatures below the wax appearance temperature. IS of waxy crude oil can be reproduced by an equivalent circuit model composed of two serially connected constant phase element-ideal resistance combinations (R-bulk vertical bar Q(bulk) - R-wax vertical bar Q(wax)). It was found that the resistor-like contribution from wax in the equivalent circuit model, R-wax, increases with the amount of precipitated wax, whereas the capacitor-like contribution in the equivalent circuit model, Q(wax), decreases with the amount of precipitated wax. Furthermore, the flow property of waxy oil, such as viscosity, can be related to the conductivity according to the fractional Walden rule. The entire viscosity-conductivity relationship can be divided into three regions, and each segment of the relationship can be fitted by the fractional Walden rule.