| Description |
Asphaltenes are one of the component fractions in crude oil and can destabilize due to a change of pressure, temperature, or composition. Destabilized asphaltenes can precipitate and deposit, causing numerous problems and challenges during oil production and processing such as plugging, fouling, and emulsion stability. Thermodynamic models were previously developed to investigate and predict the phase behavior of asphaltenes using experimental data that assumed the destabilized asphaltenes reach their equilibrium state immediately after changing system conditions. However, asphaltene precipitation has previously been shown to be a slow aggregation process suggesting that the previous thermodynamic models might be inaccurate and misrepresent the behavior of asphaltenes. Reversibility is a requirement for the application of equilibrium thermodynamics to predict the phase behavior of mixtures. In this work, asphaltene precipitation was found to be a reversible process, and the cause of the partial reversibility conclusion in previous work was discovered to be a neglected slow aggregation process. This finding reinforces the importance of a slow aggregation process as it shows that considering the kinetics can significantly alter the conclusions. The aggregation rates of asphaltenes have also previously been investigated and found that the aggregation rates of asphaltenes depend on thermodynamic driving forces. This study shows that asphaltene aggregation and deposition highly correlate with thermodynamic driving forces, but the deposit growth was governed by diffusion limitations. This investigation reveals that thermodynamic properties can directly investigate the asphaltene behavior, and the diffusion limitation finding can lead to developing a new and more accurate deposition model. In addition, for the first time, the presence of inorganic solids was observed to increase the rate of asphaltene precipitation. A model was developed to quantify the rate of asphaltene precipitation under different process conditions. This investigation leads to a clearer understanding of the complex asphaltene aggregation process that occurs in real and heterogeneous systems. The usages of inorganic solids as nucleation sites to remove unstable asphaltenes and decrease the asphaltene problems during the production are potentially possible. The findings from this dissertation emphasize the essentials of precipitation kinetics and provide ideas to decreases the asphaltene problems and understanding the behavior of asphaltenes using the thermodynamic properties. |
