Research On Stability Of Electrical Treatment Of Waxy Crude Oil

The precipitation of wax at room temperature leads to the deterioration of crude oil fluidity,which brings difficulties to the pipeline transportation of waxy crude oil.Electric field treatment of crude oil can significantly reduce its viscosity,yield stress and improve its fluidity,providing a new method for ensuring the safe operation of oil pipelines.However,in pipeline transportation,crude oil will undergo low-speed shear of pipe flow,high-speed shear of pump and heating of heat station,so it is very important to study the effect of shear and heating process on electric field modification of crude oil.However,there are few studies on the stability of the modification effect of electric field treatment,which only stays at the level of static modification effect changing with time.In view of the crude oil treated by electric field,the change rule of the modification effect(viscosity reduction,yield reduction stress)with time under static and low-speed shear conditions is studied in this paper.In static state,the effect of electric field treatment of crude oil decreases gradually with time,but it can still maintain a certain effect within 15 hours.Compared with static state,the modification effect under low-speed shear condition can maintain a longer time,and in pipe.In the flow shear range,the longer the shear rate is,the longer the modification effect will last.Through the measurement of impedance spectra of crude oil,it is found that wax crystals of crude oil are polarized after electric field treatment,and the polarization effect observed decreases with the decrease of modification effect.Through the microscopic observation of wax crystals,it is found that wax crystals accumulate and become larger after electric field treatment,and with the decrease of modification effect,wax crystals gradually return to their pre-treatment state.This indicates that the polarization and aggregation of wax crystals under electric field are closely related to the decrease of crude oil viscosity and structural strength.The research on the stability of electric field modification effect of crude oil under high-speed shearing conditions shows that the viscosity reduction effect of crude oil treated by electric field will be further strengthened after high-speed shearing(the viscosity reduction rate will be increased by more than 10 percentage points),and the viscosity reduction effect is closely related to energy dissipation during high-speed shearing process: shearing energy consumption under different shearing time and shearing rate conditions in the experimental range.The larger the energy dissipation,the higher the viscosity reduction rate.when the shear energy dissipation is the same,the viscosity reduction rate is the same.Based on this discovery,the correlation between the viscosity of modified crude oil and energy dissipation during shearing process was fitted.The experiments on the stability of the modified effect of electric field modified crude oil after heating and cooling showed that the modified effect(viscosity reduction and yield reduction stress)of electric field modified crude oil decreased after heating,and the higher the heating temperature,the greater the degree of decline;when the heating temperature was higher than the wax dissolving point,the modified effect basically disappeared;at the same time,the decrease of the modified effect was only related to heating temperature,and has nothing to do with heating times and heating rate.The number of times and the rate of temperature rise are independent.Through the microscopic observation of wax crystals,it was found that the wax crystals which became larger after electric field treatment gradually decreased and recovered to their original size with the increase of heating temperature.It was speculated that the original size of wax crystals which became larger after electric field treatment melted after heating and then precipitated after cooling,thus the modification effect decreased.The higher the heating temperature,the more the wax crystals melted after modification,the more the modification effect decreases.