Study On The Mechanism Of Magnetic Field Effect On Flowability Of Waxy Crude Oil

Magnetic treatment technology,a typical physical viscosity reduction method,has been widely employed in oilfields in recent decades.It is meaningful to systematically study the relationship between viscosity of waxy crude oil and magnetic treatment conditions for the application of magnetic treatment technology on gathering and transportation pipelines.This study profoundly studies the viscosity and microscopic characteristics of waxy crude oil under magnetic treatment by combining molecular dynamics simulation and magnetic treatment experiment.This study attempts to reveal the mechanism of magnetic viscosity reduction effects,which will help to build theoretical foundation for the application of magnetic treatment technology on gathering and transportation pipelines in oilfields.A static magnetic apparatus is designed.The magnetic intensity is able to be continuously adjusted through controlling the distance between magnets.Three typical waxy crude oils are employed to conduct magnetic treatment experiment.The relationship between viscosity reduction and magnetic treatment condition,composition of waxy crude oil and testing conditions are researched.The wax crystals and asphalt particles are observed through microscopic observation.The average diameters and size distributions of wax and asphalt particles are calculated and discussed.The sizes of asphalt particles reduce at magnetic treatment temperature and wax crystals increase at testing temperature under magnetic treatment,which is considered as the main reason for magnetic viscosity reduction effect.The grey relational theory is employed to analyze the grey correlation between viscosity reduction and magnetic treatment conditions,composition of waxy crude oil and testing conditions.The grey correlation degrees are sequentially ordered.The primary and secondary order of those influence factors on viscosity reduction are determined.A dynamic magnetic treatment experiment loop is designed.A magnetic treatment device assembled with permanent magnet is designed and installed on the loop.Orthogonal tests are conducted to explore the influence degree of magnetic treatment time,magnetic treatment temperature,magnetic intensity and velocity on viscosity reduction.The optimum treatment condition is determined.The viscosity reduction decreases with the increase of crude oil velocity.The changing trends of viscosity reduction with magnetic treatment condition are consistent with static magnetic experiment results.For profoundly researching the influence of magnetic field on wax and asphalt,determining the reason for magnetic viscosity reduction effect,Molecular Dynamics simulations are conducted to study the viscosity of waxy crude oil and mobility of molecules under magnetic treatment.The waxy crude oil model is constructed,consisting of alkanes,aromatic alkanes,wax and asphalt.The Optimized Potential for Liquid Simulations-All Atom(OPLS-AA)force field is employed to describe the interactions among atoms.The reasonability of OPLS-AA force field and waxy crude oil model is verified by comparison between simulated and theoretical density,simulated and theoretical viscosity,simulated and experimental viscosity.It is also proved that the Einstein method is suitable for viscosity calculation of waxy crude oil.The magnetic field is applied by adding Lorenz force on each charged atom during molecular dynamics simulation basing on electromagnetic theory.The molecular dynamics simulation results prove the magnetic viscosity reduction effects at molecular scale.The radial distribution function of wax and configuration of asphalt are analyzed.It is found that the wax molecules aggregate and asphalt clusters disperse under magnetic treatment,which are consistent with the microscope observation results in static magnetic experiment.The diffusion coefficient of nonane,cycloheptane,toluene and wax are also discussed in the presence and absence of magnetic field.Results show that the steric hindrance effects on molecules decrease,diffusion coefficients and mobility increase,free path of molecules extend,leading to the decrease of viscosity of waxy crude oil.