Diffusivity of Light Hydrocarbon Gases in Bitumen
Abstract
Most of the world’s heavy oil and bitumen reserves are too viscous to be produced without heating or dilution. Thermal recovery methods, which decrease the oil viscosity through heating, are widely applied in Western Canada using steam as a source of heat. Recovery processes using solvent addition to reduce viscosity are of current industrial interest because these processes have the potential to reduce water and energy requirements and could be applied to reservoirs unsuitable for thermal methods. In many solvent based processes, the solvent are gaseous hydrocarbons, and the rate of oil production is partly dependent on diffusive mass transfer of the solvent into the oil. The objective of this thesis is both to collect data and to provide a mathematical model for the diffusion of light hydrocarbons into bitumen.
There is little available diffusivity data at temperatures above room temperature. To supplement the available literature data, diffusivities and solubilities of light hydrocarbon gases in a Western Canadian bitumen were measured from 40 to 90oC and pressures from 300 to 2300 kPa, using a pressure decay method. The gas solubility is a key input into the diffusion model and additional solubility data were collected using constant composition expansion. The solubility data were fit with a modified Henry’s Law expression, which was incorporated into the diffusion model.
Existing correlations for solvent diffusivity in heavy oil have a limited range of application and do not account for the compositional dependence of the diffusivity in a physically meaningful manner. In this study, a one dimensional model of the diffusion process based on Fick’s Law was developed and fit to the pressure decay data. This model accounted for the swelling of the mixture caused by both mass transfer and the decreasing density of the solvent-oil mixture. The model also accounted for the change in viscosity with mass transfer and could be applied with any diffusivity correlation. A constant and several concentration dependant diffusivity models were assessed. The most suitable concentration dependant model was determined to be a power law relationship between the diffusivity and the viscosity of the mixture. Correlations were developed to predict both the concentration dependant and constant diffusivities with average errors of 23 and 12%, respectively, over the full range of conditions investigated.
Description
Keywords
Engineering--Chemical, Engineering--Petroleum
Citation
Richardson, W. D. (2017). Diffusivity of Light Hydrocarbon Gases in Bitumen (Doctoral thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca. doi:10.11575/PRISM/25712