Effect of Pour Point Depressants on the Impedance Spectroscopy of Waxy Crude Oil

Treatment with pour point depressant (PPD) can significantly improve the cold flowability of waxy crude oil, enabling the safe and efficient transportation of waxy crude oils through pipelines. It has been observed that the electrical properties of waxy oil, such as the dielectric constant, ζ-potential, etc., change upon PPD treatment. In a previous study, we reported that wax precipitation results in a significant change of impedance spectroscopy (IS) of a waxy oil, i.e., a second semicircle appears in the Nyquist diagram and becomes increasingly bigger with increasing amount of precipitated wax. In this study, we found that the addition of PPD may significantly reduce the second semicircle, and the more effective the PPD is, the more reduced the second semicircle will be. Equivalent circuit models suggest that the impedance characteristics of the liquid phase of wax-in-oil suspension change little with PPD addition, but the capacitance of wax particles increases and the resistance of wax particles decreases significantly. A positive correlation between the viscosity reduction and the reduction of resistance of wax particles caused by PPD is discovered. After PPD treatment, the polar functional groups in PPD molecules potentially induce charge on wax particles as they precipitate, causing the relationship between the viscosity and conductivity to approach the fractional Walden rule. This work explains the reason for the improvement of flowability upon PPD addition from a perspective of IS, which provides some new proofs to understanding the functional mechanism of PPD.