Study On The Structural Characteristics Of Electrically Treated Waxy Crude Oil

Waxy crude oil has poor fluidity and complicated rheological characteristic below its gelation temperature.Studies shown that direct current(DC)electric field technique can significantly reduce the viscosity of waxy crude oil below its wax appearance temperature,but the effect on structural characteristics of waxy crude oil is not clear and systematic.In the present study,based on electrorheological principles,the structural properties of waxy crude oil with different DC electric field strength and treatment temperature were investigated with the help of electric field device developed by our research group.Furthermore,the effect of DC electric field on the restart of crude oil pipelines was calculated.First of all,viscoelastic behaviors of waxy crude oil were studied by small amplitude oscillatory shear(SAOS)and creep-recovery experiments.The results showed that high-voltage electric field near the pour point can significantly weaken the elastic dominant position,reduce the storage modulus,shorten aging hours and decrease the structure strength.In addition,lower treatment temperature and higher intensity electric field can provide weaker gel structure strength of waxy crude oil.Secondly,yield behaviors of waxy crude oil with DC electric field were studied by stress linear loading experiments.It was found that at the same treatment temperature,yield stress decreased with the electric field strength increasing.The reduction of yield stress increased more especially under lower test temperature.While yield strain had no obvious change with electric treatment.Thirdly,thixotropic behaviors of waxy crude oil with DC electric field were studied by both stepwise-increase in shear rate and hysteresis loop experiments.Through experimental analysis with the elasto-viscoplastic thixotropic mode,it was seen that DC electric field can weaken the thixotropy of waxy crude oil,accelerate its structural breakdown,make the oil tend to be Newtonian fluid.Finally,with the help of numerical calculation methods,the effect of electric field treatment on the restart of waxy crude oil pipelines was studied.The results showed that high-voltage electric field can reduce the minimum restarting pressure required for crude oil pipelines and shorten the computed time for the outlet to start to flow.With the increase of electric field strength,the relevant changes were more obvious.In summary,DC electric field technique can significantly reduce the gel structure strength of waxy crude oil,and be beneficial to the restart of crude oil pipeline at low temperature.The present research work about DC electric field technology can lay a foundation for the application of oil transportation engineering.