| dc.description.abstract | The study of the asphaltene precipitation problem during CO2 Enhanced Oil Recovery (EOR) under different reservoir conditions is addressed in this thesis. The general objective of this investigation is to effectively predict asphaltene precipitation using a thermodynamic model. More specific objectives are (a) measuring, comparing, and modeling the saturation points for crude oil and gas injection systems, (b) measuring asphaltene content and asphaltene onset pressures (AOP), (c) analyzing asphaltene-oil-CO2 phase behavior and reversibility mechanisms, (d) determining asphaltene precipitation weight, and (e) tuning an equation of state (EOS) and a solid model to predict the experimental data using WinProp (CMG, 2011).The experimental determination of the total asphaltene content in the oil sample is performed following the laboratory standard, ASTM D-3279. Afterward, an advanced fully visual Pressure-Volume-Temperature (PVT) instrument and a Solid Detection System (SDS) are utilized to perform all the saturation pressure and AOP measurements in this work. These two pieces of equipment include a high-resolution camera through which the developed phase behaviors and asphaltenes particle characterization are observed at different pressure and temperature conditions.From the experimental results, the saturation pressures for all the CO2-oil mixtures increase directly with CO2 concentrations and temperature. The upper asphaltene onset pressures (UAOP) increase with CO2 concentrations in the system and decrease with temperature increments. In contrast, the lower asphaltene onset pressure (LAOP) increases with CO2 concentrations and temperature increments in all cases. For 25 mole% of CO2 at 60, 90, and 120 °C, the reversibility of the asphaltene precipitation process is corroborated. However, irreversible asphaltene precipitation processes are found for 35, and 45 mole% of CO2 injected at 25 °C. The maximum quantity and most significant size of asphaltene precipitation particles are found at bubble point for all cases. Asphaltenes particles do not have a specific shape, and their colors vary from brown to black. The reversible asphaltene mechanisms developed four different phase behaviors during the isothermal depressurization. In contrast, the irreversible asphaltene mechanisms developed only three phase behaviors.The crude oil sample characterization and modeling calculus are performed using commercial software, WinProp, from Computer Modelling Group Ltd. (CMG). The model reproduced the experimental saturation pressure measurements by tuning the Peng-Robinson EOS. A solid model is used as a thermodynamic equation. The purpose is to predict asphaltene precipitation under different CO2 mole% injections for isotherms at 25°C, 60°C, 90°C, and 120°C. This thermodynamic model calculates fugacity of the liquid phase from the tuned Peng-Robing EOS to predict the asphaltene precipitation wt%. Then it is adjusted manually for different solid molar volume parameters. The experimental asphaltene precipitation wt% was successfully modeled for various CO2 mole% injections for isothermal conditions. A new correlation of the molar volume in function of temperature and CO2 molar concentrations was developed. The developed correlation successfully predicts the solid molar volume required to match the experimental asphaltene precipitation wt% with an absolute average relative deviation (AARD) of 0.75%. | |
