Determination of Solubility Parameter of Methane in Heavy Oil
Date
2021-06-24
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Abstract
Asphaltenes are the least soluble fraction of crude oil and can phase separate from the oil due changes in pressure, temperature, or oil composition. Some examples where asphaltene precipitation occur in oilfield operations are: dilution of a heavy oil with an incompatible solvent (e.g. an n-alkane), depressurization of a light conventional oil during production, and gas injection into a light conventional oil reservoir. Methane is often a major component of the dissolved gases in a crude oil and has a significant negative impact in the oil’s ability to solubilize asphaltenes. The Modified Regular Solution (MRS) model has been previously used to model asphaltene precipitation from heavy oils and bitumen diluted with n-alkanes at different temperatures and pressures. The input parameters of the MRS model are the mole fractions, molar volumes, and solubility parameters of the bitumen (characterized into SARA fractions), and the n-alkane solvent. However, the MRS model is not yet able to predict asphaltene solubility in the presence of dissolved gases, such as methane, because the solubility parameter of the dissolved methane is unknown. To determine these parameters, asphaltene onsets and yields from mixtures of bitumen, n-pentane, and methane were measured at temperatures of 21 and 130°C and pressures of 10 and 60 MPa. The onsets (solvent content at which precipitation first occurred) were measured by titrating the bitumen with a mixture of methane and n-pentane in a High-Pressure Microscope. Asphaltene yields (mass of asphaltenes divided by mass of bitumen in feed) were measured in a blind cell apparatus for mixtures with the same methane content as the onset measurements. The methane solubility parameter was determined by fitting the MRS model to the measured asphaltene precipitation data. The fitted values ranged from 6.1 to 9.5 MPa0.5 depending on the temperature. A correlation for the methane solubility parameter was developed for use in the MRS model. The MRS model using the correlation matched the onsets and yields with average deviations of 1.1 wt% solvent and 8.1 wt%, respectively. The updated model now applies to in situ heavy oils that contain dissolved methane.
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Keywords
Asphaltene Precipitation, Bitumen, Phase Behavior, Solubility Parameter, Methane
Citation
Paniagua Fernández, D. (2021). Determination of Solubility Parameter of Methane in Heavy Oil (Master's thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca.