Equation of state modeling of phase behaviour of bitumen/co2/propane mixtures
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2009
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Abstract
Among the various methods for modelling the phase behaviour of crude oils, the equation of state (EoS) approach is the most commonly used. To employ an EoS, the critical properties, acentric factor, molecular weight, and binary interaction parameters of the constituent components are required to characterize the fluid. For conventional oils, techniques such as distillation can be used to generate a true boiling point (TBP) curve which can be cut into pseudo-components. However, with heavy oils, less than 50% of the oil cannot be distilled and some extrapolation methods are required to complete the TBP. The objective of this thesis is to test different extrapolation techniques against a relatively comprehensive data set. The data set included vapour-liquid (VL), liquid-liquid (LL), and vapour-liquid-liquid (VLL) phase boundaries for mixtures of propane, carbon dioxide and Athabasca bitumen. Some data on phase volumes and compositions were also collected. Asphaltene precipitation data were also available for n-heptane diluted Athabasca bitumen. Simulated distillation data for the maltenes were used to characterize the distillable fraction of the bitumen. The non-distillable fraction was characterized using two different methods: I. Model A: the distillation data for maltenes was linearly extrapolated to an assumed end point; 2. Model B: the linear extrapolation was stopped at the end of the maltene and the asphaltene TBP were determined based on a Gamma distribution of their assumed molar mass distribution and well-established property estimation correlations. Each characterization, including critical properties determined from correlations, was input into the Peng-Robinson EoS. The binary interaction parameters between the solvent and each bitumen pseudo-component were adjusted to fit experimental saturation pressure data using a regression program. The sensitivity of the model to the assumed TBP end point and assumed molar mass distribution was examined to determine the optimum characterization. The sensitivity to the number of pseudocomponents in the characterization was also assessed. Both models provided good fits of the saturation pressures at the L/VL and LL/VLL boundaries. Both models were able to provide a qualitatively accurate prediction of the extended phase diagrams of the binary mixtures of propane/bitumen and carbon dioxide/bitumen including L, LL, VLL, and VL regions. However, only Model B correctly predicted the LL and VLL regions of the ternary mixtures of propane, carbon dioxide, and bitumen. While both models could be tuned to match the onset of asphaltene precipitation from n-heptane diluted bitumen, they significantly underestimated the yield at high dilutions.
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Bibliography: p. 98-104
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Citation
Modaresghazani, J. (2009). Equation of state modeling of phase behaviour of bitumen/co2/propane mixtures (Master's thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca. doi:10.11575/PRISM/3146