Measurement and Modeling of Pentane-Diluted Bitumen Phase Behaviour
Abstract
The phase behavior of mixtures of bitumens and n-alkanes is a key factor in the design and optimization of solvent-assisted heavy oil recovery processes and solvent deasphalting processes. However, data and comprehensive models are lacking for these mixtures. Crude oil phase behavior is typically modeled using cubic equations of state (CEoS). While CEoS have successfully fit saturation pressures and asphaltene onset points for bitumen-solvent systems using simple quadratic mixing rules; they do not accurately predict asphaltene precipitation yields. This thesis focuses on data collection and CEoS modeling with asymmetric mixing rules for mixtures of bitumen and n-pentane.
Phase behavior data were collected for n-pentane diluted bitumen up to 14 MPa and 280°C. Saturation pressures were measured using both a PVT cell and a blind cell apparatus. The composition at which asphaltenes precipitate was measured using a high pressure microscope apparatus and was extrapolated from asphaltene yield data. A new experimental procedure was developed to measure the phase compositions of both the light phase and the asphaltene rich heavy phase at high temperature where two liquid phases are observed. A blind cell apparatus was designed to measure asphaltene yields for multiple samples simultaneously. Binary and ternary phase diagrams were generated from the data.
The Advanced Peng Robinson (APR) CEoS with several sets of asymmetric and compositionally dependent mixing rules was evaluated using the aforementioned dataset. The use of asymmetric mixing rules significantly improved the match to asphaltene yield data; however, the yields were still under-predicted at high solvent contents and the tuning parameters that gave the best match for asphaltene yield data were not predictive or easily correlated for other solvents. The use of compositionally dependent solvent/asphaltene binary interaction parameters allowed the model to fit asphaltene yield data over the entire composition range. A set of interaction parameters was recommended that fits both asphaltene yield and saturation pressure data. While successful at fitting the data, this approach is not practical for many simulation applications and the overall conclusion is that CEoS are not well suited for the full range of bitumen-solvent phase behavior.
Description
Keywords
Engineering--Chemical, Engineering--Petroleum
Citation
Johnston, K. (2017). Measurement and Modeling of Pentane-Diluted Bitumen Phase Behaviour (Doctoral thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca. doi:10.11575/PRISM/26844