Flow behavior of waxy crude oils under electric field: Effect of their dielectric constants

At low temperatures, crude oils exhibit high viscosities, viscoelastic moduli, and yield stresses due to wax crystallization and network formation, making their transportation through pipelines challenging. We study six crude oils of varying origin, composition, and dielectric properties and show that electric field application can disrupt these wax networks and improve flowability. First, the effect of wax crystallization on the rheology of crude oils was studied. By comparing viscosity versus volume fraction of crystalized wax with Krieger–Dougherty equation, corrected volume fractions were estimated to account for the highly aspherical and aggregated nature of wax particles. The final viscosities and moduli of all crude oils were found to correlate with the effective volume fractions. Then, the electrorheological response of all crude oils was studied under shear and stationary conditions. The viscosities of all crude oils decreased exponentially with time during electric field application. Under static conditions, the storage moduli, yield stresses, and yield strains also decreased significantly with electric field application. These reductions in rheological parameters are explained through the compressive Maxwell stress acting on the wax particle, which vary inversely with (2εoil−εwax) (εoil and εwax being dielectric constants of the oil and solid phases, respectively). We correlate the rate constant of viscosity decrease and the reductions in storage modulus, yield stress, and yield strain with the dielectric properties. Overall, this study provides insights into the use of electric fields to enhance the flowability of waxy crude oils with varying dielectric properties and their potential use to address challenges related to flow assurance.