A thermodynamic polydisperse polymer model: Asphaltene flocculation, aggregation and deposition

It is well recognized that the existence of asphaltene in crude oil can add significantly to the petroleum field problems. This may result in asphaltene deposition inside the reservoir which is likely to affect the efficiency and cost of petroleum production. To prevent deposition inside the reservoir, in the well head, and inside the transmission line, it is necessary to be able to predict the onset and amount of deposition due to various factors. Development of a predictive model which describes the phase behavior of asphaltene is limited because of the complex nature of heavy organic substances such as asphaltene, resin, and other heavy components. In this dissertation the basic mechanisms of asphaltene deposition are described based on different microscopic theories. The statistical mechanical thermodynamic theory of heterogeneous polymer solution and kinetic theory of fractal aggregation are utilized for the case of mixtures consisting of miscible solvent and polydisperse asphaltene with a wide range of molecular weight. Application of the principles of thermodynamics of multicomponent mixtures and phase equilibria to the theory of polymer solutions and kinetic theory of fractal aggregation has enabled the development of a thermodynamic model where the phase behavior of asphaltene due to introduction of miscible solvents is predicted. The role of interaction between a polydisperse asphaltene and miscible solvent and its effect on the predictive capabilities of a model are discussed. This model is able to properly describe the growing mechanism of asphaltene aggregates, the growing size distributions of asphaltene, and the geometrical aspect of asphaltene aggregates. The model is also used for predictions of the phase behavior and deposition region of asphaltene in reservoir fluids composed of oil and miscible solvents at high pressures and various temperatures. The proposed model can provide a tool for controlling the asphaltene deposition in enhanced oil recovery processes.