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Fossil Fuels
An Experimental and Modeling Study on Interactions of Cold Lake Bitumen with CO2, C3, and C4 at High Temperatures Sara Eghbali, and Hassan Dehghanpour Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.8b04444 • Publication Date (Web): 14 Mar 2019 Downloaded from http://pubs.acs.org on March 26, 2019
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Energy & Fuels
An Experimental and Modeling Study on Interactions of Cold Lake Bitumen with CO2, C3, and C4 at High Temperatures Sara Eghbali , Hassan Dehghanpour Department of Civil & Environmental Engineering, University of Alberta, Alberta T6G 2W2, Canada
Abstract Co-injecting solvents like CO2 and light hydrocarbons with steam into bitumen reservoirs can improve the efficiency of SAGD (Steam Assisted Gravity Drainage) process by reducing Steam Oil Ratio (SOR). The effects of these solvents on bitumen recovery enhancement depends on reservoir properties and operating conditions. To investigate the effects of solvents on bitumen viscosity in a Solvent Aided Process (SAP), phase behavior and viscosity of CO2-, C3-, and C4bitumen systems were measured and modelled at high temperatures. Using the calibrated PengRobinson Equation of State (PR-EOS), the solubilities of solvents in Clearwater bitumen sample from Cold Lake region were predicted. A high pressure-high temperature (HPHT) equipment using an electromagnetic-based viscometer was customized to measure the liquid viscosity of CO2-, C3-, and C4-bitumen mixtures. The measured viscosity data were used to calibrate a nonlinear viscosity model. This model was then used to predict liquid phase viscosity as a function of solvent solubility and temperature. The effects of solvent dissolution on bitumen viscosity were investigated using PR-EOS and the calibrated viscosity model. The results show that dissolving CO2, C3, C4 in bitumen decreases its viscosity. This viscosity decrease is lowest and highest in the case of CO2 and C4 dissolution, respectively. The effect of solvent dissolution on viscosity reduction is more pronounced at lower temperatures. EOS predictions and viscosity measurements indicate that increasing solvent (i.e., CO2, C3 and C4) concentration above a certain threshold has limited effect on reducing bitumen viscosity. At threshold solvent concentrations, bitumen viscosity can be reduced by 1.7, 5.6 and 15.2 times by CO2, C3 and C4, respectively at 120°C. Solubility and viscosity data show that C4 has the potential to be used in hot solvent recovery methods in shallow and deep oil sand reservoirs. C3 may be a more effective solvent in deeper reservoirs during hot solvent and solvent aided processes. The modified viscosity model showed better performance compared with Lobe and Shu correlations and logarithmic mixing rule. This model improves on existing correlations for predicting liquid viscosity of light solvent-bitumen mixtures by requiring less input data and does not require density data. Also, this model is simply applicable in thermal reservoir simulators. The experimental solubility and viscosity data from this study can be used to optimize the recovery from solvent-based and solvent aided processes.
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1. Introduction Studying solvent-bitumen interactions is of great interest as the industry seeks to improve hydrocarbon recovery from oil-sand resources using steam- and solvent-based recovery processes. Solvent Aided Process (SAP) is a steam-based recovery process proposed to improve SAGD efficiency and reduce associated emissions by reducing Steam Oil Ratio (SOR).
1.1. Solvent Aided Process In SAP, energy efficiency can be enhanced by adding solvent to the injected steam to reduce viscosity by a combination of heat and mass transfer effects [1]. Simulation and experimental studies using a wide range of solvents (including pure hydrocarbons from C5 to C8) show higher oil production rates in SAP compared with those in conventional SAGD process [3-7]. An experimental study based on microfluidics approach [8] showed that co-injecting diluents with steam enhance SAGD recovery factor up to 14%. Light solvents such as CO2, C3, and C4 may also be efficient for reducing heavy oil viscosity and improving oil recovery [1; 9-15]. An experimental pore-scale study showed bitumen dilution and production by hot C3 and C4 in a condensing front [16]. The dilution of bitumen with solvent drastically reduces bitumen viscosity during SAP [17]. Therefore, it is necessary to measure viscosity of the diluted bitumen and obtain a viscosity model based on experimental data under SAP conditions.
1.2. Liquid-Phase Viscosity Measurements Viscosity of bitumen diluted with light hydrocarbon solvents has been measured and reported in literature. Table A-1 summarizes the viscosity experiments for mixtures of light solvents and heavy oil/bitumen available in the literature. Similarly, the pressure and temperature effects on bitumen viscosity saturated with N2, CO, CO2, C1, C2, C3, and C4 have been previously studied [18-22]. Badamchi-Zadeh et al. [14] measured the viscosity of Athabasca bitumen saturated with C3 between T=10°C and T=50°C. Freitag et al. [23] measured the viscosity of a C3-Lloydminster oil system at T
