Determination of Solubility Parameter of Carbon Dioxide in Heavy Oil
Date
2020-05-06
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Abstract
Asphaltene precipitation and the subsequent deposition of asphaltenes can damage the reservoir and foul surface equipment and pipelines. Hence, there is a need to predict at what composition, temperature and pressure asphaltenes will precipitate from crude oils. The Modified Regular Solution (MRS) approach has been used to model asphaltene precipitation in heavy oils diluted with solvents. This model has not yet been rigorously applied to asphaltene precipitation from depressurized live oils (oils with dissolved gases) partly because the solubility parameters of the dissolved gases are required, but not known. The objective of this study is to determine the solubility parameter of dissolved carbon dioxide (CO2). Live oils were prepared from Western Canadian bitumen and CO2 and the bitumen and live oil phase behavior was measured from 20 to 130°C and pressures from 0.1 to 60 MPa. The densities were measured in a vibrating tube density meter. The onsets of asphaltene precipitation from the oils diluted with n-pentane were measured visually using a high pressure microscope (HPM). Asphaltene yields of the oils mixed with n-pentane were measured in a blind cell apparatus. The solubility parameter of dissolved CO2 was determined by fitting the MRS model to the asphaltene onsets and yields from the live oils. The model was fitted by adjusting the dissolved gas solubility parameters; all of the other model inputs were known. As the CO2 content in the live oil increased, the amount of n-pentane required to initiate precipitation decreased and the yield increased; that is, the asphaltenes became less soluble confirming that CO2 is a poor solvent for asphaltenes. When CO2 was present, precipitation occurred in two stages: low yields up to 12 wt% n-pentane above the initial onset followed by a dramatic increase in yield at higher dilutions. The model could not represent both stages and a correlation for the carbon dioxide solubility parameter was developed based only on the second stage yields. Discrepancies in the model are attributed to the use of a one-dimensional solubility parameter that accounts for dispersion force interactions not for polar or hydrogen bonding interactions which can be significant for CO2.
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Keywords
Asphaltene precipitation, Phase Behavior Modeling, Thermodynamic Modeling, Carbon Dioxide, Heavy oil, Solubility Parameter, Regular Solution Model
Citation
Ferreira Cala, J. N. (2020). Determination of Solubility Parameter of Carbon Dioxide in Heavy Oil (Master's thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca.