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EXPERIMENTAL INVESTIGATION OF THE SETTLING VELOCITY OF SPHERICAL PARTICLES IN VISCOELASTIC FLUIDS
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- Author / Creator
- Arnipally, Sumanth Kumar
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Knowledge of settling behavior of particles in various types of fluids is indispensable to design and optimize numerous industrial operations such as cuttings transport in oil and gas well drilling, proppant transport in hydraulic fracturing operations, and so on. Most of the models developed so far were to predict settling velocity of particles in either Newtonian or purely viscous non-Newtonian shear thinning fluids where there were no considerations of the fluid elasticity effect. Therefore, these models are not suitable for settling velocity prediction when the process involves fluids of viscoelastic nature such as drilling and hydraulic fracturing fluids. The main objective of this study is, therefore, set to determine how the fluid shear viscosity and the elasticity would influence the particle settling velocity and even more so to answer the question of which one of these two rheological properties is more dominant in controlling the particle settling velocity when viscoelastic drilling fluids are used. The settling velocities of the spherical particles (diameters: 1.18, 1.5, 2 and 3mm) in partially hydrolyzed polyacrylamide (HPAM) polymer fluids were measured by using Particle Image Shadowgraph (PIS) technique. Two sets of test fluids were formulated by mixing three different grades of HPAM (molecular weights of 500,000; 8,000,000; and 20,000,000) at polymer concentrations 0.09%, 0.05% and 0.03% wt. The shear viscosity and elasticity characteristics of test fluids were determined by performing shear viscosity and frequency sweep oscillatory measurements, respectively. The first set of fluids had almost identical shear viscosity characteristics while showing significantly different elastic properties. The second set of fluids had similar elastic properties but different shear viscosity characteristics. Experimental results showed that: (i) When the fluids having similar shear viscosity profile were used, the settling velocity of spherical particles decreased significantly with the increasing fluid elasticity. Comparison of the experimental results against the values calculated from the model developed for predicting the settling velocity of spherical particles in power law (visco-inelastic) fluids have shown that the settling velocity values can be 14 to 50 times over-estimated if the effect of the elasticity is not considered; (ii) At constant elasticity, the settling velocity of spherical particles also decreased significantly when the fluid shear viscosity was increased; (iii) The spherical particles settling velocity increased pronouncedly as their diameter increased from 1.18mm to 3mm. But the magnitude of the increase in settling velocity with the increasing particle diameter is less for the samples having higher elasticity and similar shear viscosity characteristics. A follow up experimental study has been conducted to understand the reasons behind why the settling velocity of the particles decrease with the increasing fluid elasticity. In this case, the main objectives were: (i) to investigate the fluid flow field behind the settling particle by using particle image velocity (PIV) technique; (ii) to understand the changes caused by the elasticity of the fluid on the flow field past the settling particle; (iii) more specifically, to determine how the fluid velocity profile and the resultant drag forces acting on the settling particle change with the increasing fluid elasticity. Two sets of viscoelastic fluids were formulated by mixing three different grades of partially hydrolyzed polyacrylamide (MW of 500,000; 8,000,000; and 20,000,000) at polymer concentrations of 0.09%wt and 0.1%wt. The viscoelastic fluids were formulated in such a way that they had almost identical shear viscosity but significantly different elastic properties. The fluid flow field (i.e. near particle velocity profile) behind the settling particle was determined by using the PIV technique. The results of the PIV measurements demonstrated that negative wake was present in viscoelastic fluids. However, the stagnation point (the point at which fluid velocity becomes zero and above that the fluid starts moving in the opposite direction to the particle movement) was closer to the particle settling in the higher elasticity fluid than that in the lower elasticity fluid. The velocity of the fluid in the recirculation region was higher for the flow of the fluid with higher elasticity. Therefore, the presence of stronger negative wake having fast moving fluid in reverse direction nearer to the settling particle could possibly create higher drag forces (acting in the direction against the particle movement), which would affect the settling velocity of the particle.
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- Graduation date
- Fall 2017
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- Type of Item
- Thesis
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- Degree
- Master of Science
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- License
- This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.