Asphaltene particles in crude oil tend to deposit upon changes in chemical composition, thermodynamic parameters such as pressure and temperature, or injection of gasses during enhanced oil recovery, leading to serious operational issues as well as economic costs. This thesis investigates asphaltene particle deposition in a horizontal pipeline, focusing on developing a novel model to simulate asphaltene particle behaviour using the population balance model over an extended pipe length. While the population balance model has been traditionally applied to account for aggregation and breakage, this research introduces a new population balance model that incorporates both deposition and aggregation processes taking place simultaneously, which has never been explored in the literature. Unlike aggregation and breakage, the deposition kernel is undeveloped. In this research, the deposition kernel and size-dependent functions were obtained from the Discrete Phase Model (DPM) within ANSYS Fluent. The turbulent fluid flow in the pipe was simulated using computational fluid dynamics (CFD), whereas particles and their related process of transport and deposition were tracked and simulated using DPM. The simulations were conducted in an industrial-size 10-meter horizontal pipe under turbulent flow conditions. The required meshing and mesh sensitivity analysis were performed to optimise the accuracy of the simulation results. The horizontal pipe was sectioned in the axial direction to capture the deposition profile in the flow direction (z-axis) under different flow velocities. Data obtained from the computational fluid dynamics simulation were used to derive model coefficients of the deposition kernel in the PBM deposition term. which were then employed in solving two population balance equations: one for the steady-state fluid-particle deposition and aggregation, and another for the transient particle deposition on the pipe wall. The computational fluid dynamics simulation using the discrete phase model showed that asphaltene deposition increases with increasing particle diameter and particle concentration. However, the deposition decreases with increasing fluid velocity. DPM results showed that increasing velocity from 0.1 m s-1 to 1 m s-1 led to a 7% decrease in deposition flux on the inner surface of the pipe. Furthermore, increasing fluid velocity beyond 5 m s-1 had a negligible effect on asphaltene deposition. Deposition decreased by 52% when fluid velocity was increased to 10 m s-1 relative to 0.1 m s-1. Even though asphaltene deposition was decreased by more than half, fluid velocity increased by a 100-fold. All DPM results of deposition trends were in agreement with the literature data. The deposition rate constants obtained from DPM were moderately accurate but varied by position along the pipe. The model showed model fit R2 as high as 0.67 in some locations, whereas it performed poorly at other locations. Nevertheless, this model was used in the PBM model in a pipe of 500 m in length. The initial particle size ranged from 0.1 micron up to 32 microns; however, the particle size distribution reached a size of 516 microns due to aggregation of smaller particles after PBM modelling. The model developed was successful in predicting asphaltene deposition in the extended pipe length. The steady and unsteady population models showed promising results in their ability to predict both aggregation and deposition. Additionally, the model also provided insights into the dynamics of deposit build-up and the total thickness of deposits along the axial direction over time. The steady-state population balance model showed that asphaltene particle number density in the system decreases rapidly in the first section of the pipe, indicating a deposition process taking place and dominating over aggregation. This is confirmed by the third moment of the particle population. PBM findings showed that deposition dominated the first 100 m of the pipe; however, deposition slowed after that, and the flow was dominated by the aggregation process. This is proved by the increase in 4-3-moment (average size) after 100 m, which is an indication of the growth in size by the aggregation of smaller particles. This trend was observed for all velocities. The mean size reached after 100 s of the simulation was greater at lower velocities compared to high velocities. The unsteady-state population model demonstrates the accumulation of particles on the wall over time. The results showed that the deposition primarily takes place at the beginning section of the pipe, which then slows down. Furthermore, the rate of deposition was greater at lower velocities compared to relatively low deposition rates at higher velocities. For instance, at 1 m s-1 the deposition takes place gradually over time, reaching 8 mm thickness after 100 s. The same trend was observed with other velocities, e.g., with 5 m s-1 and 10 m s-1, the accumulation is approximately 5 mm after 100 s with slightly higher at velocity 5 m s-1. The results show that the total thickness reached after approximately 17 minutes is 8 cm for 1 m s-1 velocity. Whereas the maximum thickness reached with velocities 5 and 10 m s-1 were 5 cm with slightly lower at velocity 10 m s-1.
| Date of Award | 19 Sept 2025 |
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| Original language | English |
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| Supervisor | Lande Liu (Main Supervisor) & Slava Stetsyuk (Co-Supervisor) |
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