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Numerical Simulation of Sand Retention Mechanisms
- Author / Creator
- Seyedehfatemeh Razavi
The primary motivation of this research is to investigate the conditions and parameters that influence the formation, stabilization, destruction and reformation of the multi-particle sand arching (bridging) that occurs at the opening of the sand filters to support sand retention. In particular, this research will examine the performance of the multi-particle arch under transient fluid flow conditions.
The computational fluid dynamic (CFD) - discrete element method (DEM) model is applied to predict multi-particle arch formation, stabilization, breakage and reformation under steady and transient flow conditions of the well-bore. By using coupled CFD-DEM (CFD to model the fluid flow, and DEM to model the particle flow), the physics involved in the multi-particle arching phenomenon is studied and industry-relevant problems are investigated. The coarse grid unresolved and the smoothed unresolved (refined grid unresolved) coupling approaches implemented in STAR-CCM+ (SIEMENS PLM) are used to transfer data between the fluid and solid phases and calculate the forces. The filter slots under investigation have different geometries: straight, keystone, wire-wrapped screen (WWS) and seamed slot and the particles are considered with different shapes and different aspect ratios and size distributions. The flow regime is laminar in all simulations conducted.
The CFD-DEM model is validated from the perspectives of particle-fluid, particle-particle and particle-wall interactions. Verification of the CFD-DEM model is conducted by mesh sensitivity analysis to investigate the coupling resolution between the CFD and DEM.
Various simulations of the sand retention mechanisms with the slurry flow and unstable/stable packed-bed cases, under steady and transient flow conditions, at the opening of filters are conducted.
Surface deposition, size exclusion and sequential arching of particles are observed as retention mechanisms with the slurry flow, whereas multi-particle arching is observed in packed beds only. The importance of the gravity force and interaction forces on retention mechanisms are confirmed at the micro-scale in comparison with the drag force, lift force, cohesive force, buoyancy force and virtual mass force. Multi-particle arching occurs after several particles flow through the opening. The ratio of the particle size to the sand screen opening is an important factor in arch formation.
At the micro-scale, multi-particle arching is controlled mainly by particle interactions, particle concentration, and particle-domain interactions. The results confirm that bridge formation and stability are controlled by particle shape, relative slot size-to-particle size, and interaction forces between particles forming the bridge. The results also show that two forces are critical to forming the multi-particle arch: gravity force and interaction forces between the particles and particle-domain at the micro-scale. The results show that multi-particle arching is the result of particle interaction and surface deposition at the slot entrance.
Particle size distribution supports the multi-particle arch and the arch stays stable for a longer time than the case with the uniform-size distribution of particles. Particle shape affects the arch stability with non-spherical particles with sharp corners resulting in a more stable arch, as long as the aspect ratio of particles is not too large.
A stable packed bed supports stabilization of the multi-particle arch. Instabilities caused by transient flow changes, such as flow interruptions, can result in arch breakage and increased sand production. A curved surface at the slot entrance, such as the modelled simplified seamed slot shape, can result in lower arch stability and more sand production.
- Graduation date
- Fall 2021
- Type of Item
- Doctor of Philosophy
- 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.