Effect of residual oxygen in combined co2 flooding and sequestration process
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AbstractCarbon dioxide flooding is a well-established enhanced oil recovery process. The cost of a combined CO2 miscible flood/sequestration process depends on the purity of injected CO2 stream. Oxygen contaminant is of particular interest as it can modify the native oil properties through low temperature oxidation reactions; promote corrosion in the piping. This study investigated the influence of various levels of oxygen as an impurity in CO2 on the selected light oil. Effects of oxygen concentration in the feed gas reaction temperature, pressure, time and the presence of core matrix and brine on compositional changes and rheological properties in the partially oxidized oil have been investigated. It was found that the asphaltenes and coke yields of the reacted oil were higher than the original oil's values following the injection of pure CO2 or CO2/O2 gas mixtures. Asphaltenes plus coke yields increased with increasing temperature when oxygen was present. The presence of core promoted the production of asphaltenes but retarded the formation of coke. It showed that asphaltenes plus coke contents increased smoothly with increasing oxygen concentration in the feed gas. With enough reaction time, the sum of coke and asphaltenes would flatten out when the oxygen concentration was above 5 mol%. Viscosities and densities of the modified oil were higher than those of the original oil. Phase behavior observations and swelling experiments for different concentrations of CO2/O2 mixtures injected into the light oil were conducted to investigate the complex phase phenomenon that occurred during the carbon dioxide flooding process. Multi-phase equilibrium calculations were conducted to predict the component distribution. The effect of oxygen/carbon dioxide gas mixtures on Athabasca bitumen was studied in this thesis. The results showed influence of the gas mixtures on compositional changes and rheological properties of the Athabasca bitumen. A kinetic model for describing low temperature oxidation reactions was developed. It explained the mutual conversion between the maltenes and asphaltenes, and the oil compositional changes as a function of the reaction time. Development of this kinetic model provided a better understanding of the reaction mechanism when an oxygen containing gas was injected into a reservoir.
Bibliography: p. 258-268