Research On The Sedimentation Law Of Particles In Viscoelastic Fluids

In the oilfield due to the formation of sand,there will be sand particles in the wellbore movement,as polymer flooding in the oilfield more and more widely used,see more and more polymer oil wells,and the movement law of sand particles in polymer flooding oil wells and water flooded oil wells is not consistent,because the polymer solution has viscoelasticity,therefore,it is necessary to study the sedimentation law of particles in viscoelastic fluid.In this paper,a set of sedimentation experimental device for particles in a round tube is established,the sedimentation velocity and sedimentation trajectory of particles in viscoelastic fluids are measured,and the factors affecting the sedimentation law are analyzed.In this paper,a single-particle sedimentation experiment was carried out to measure the sedimentation velocity of smooth aluminum balls and steel balls of different diameters in polymer solutions of different concentrations,and an empirical formula for calculating stable sedimentation velocity was fitted according to the experimental results.The final sedimentation rate of particles is related to parameters such as particle size,particle and solution density,and solution viscosity.Because the polymer solution is a shear thinning fluid,its viscosity decreases with the increase of shear rate,that is,the viscosity of the solution changes with the sedimentation rate of particles.In order to determine the viscosity during the particle sedimentation process,this paper first solves the fluid velocity field around the particle through theoretical analysis,and obtains the relationship between the shear rate of the fluid and the particle sedimentation velocity.Combined with the rheological curve of the polymer solution,the viscosity of the fluid during particle sedimentation is finally obtained.Overshoot occurs when particles settle in a viscoelastic fluid,that is,particles accelerate and reach a higher velocity than the stable velocity as they settle,and then slow down to a stable velocity.Its overshoot velocity,that is,the maximum velocity of sedimentation,is not much different from the stable velocity of particles in Newtonian fluids under the same experimental conditions.Its overshoot,i.e.the ratio of overshoot velocity to stable velocity,is proportional to the Weissenberg Number of the solution.In this paper,the sedimentation experiments of parallel double particles were performed to measure the sedimentation trajectories of smooth aluminum balls and iron balls of different diameters in polymer solutions of different concentrations.The double particles settle in a low-concentration polymer solution,and as the relative spacing of particles(particle spacing/particle diameter)increases,the particles will gradually change from being close to each other and moving away from each other until they do not affect each other;The sedimentation law of double particles is similar to that of low-concentration solutions,but the relative spacing between particles when they are far away from each other is larger than that of low-concentration solutions.The double particles settle in a highly concentrated polymer solution,and as the relative spacing of the particles(particle spacing/particle diameter)increases,the particles gradually change from being close to each other to not affecting each other.According to the analysis of experimental results,it is found that when the particles are close to each other,the ratio of elastic number to relative spacing is greater than 1.When particles move away from each other,the ratio is less than 1.Finally,a chain particle sedimentation experiment was performed to measure the maximum number of particles that the particle chains of different particles maintained in the chain shape in different concentrations of polymer solutions.Its maximum particle number is proportional to the polymer solution concentration and inversely proportional to the particle density.The disconnection method of the particle chain is related to the Reynolds number,when the Reynolds number is low,the particle chain will be broken at the tail;When the Reynolds number is high,the particle chain breaks in the head.The results of this study have certain theoretical significance for the in-depth understanding of the motion law of particles in viscoelastic fluids.