Use of CO2 in Vapex, Experimental and Modeling Study
Creators: name: Badamchi Zadeh, Amin
Publisher: name: Graduate Studies
Year: 2013
Subjects: subject: Engineering--Chemical
subject: Engineering--Petroleum
subject: Vapex
subject: Phase Behaviour
subject: Heavy Oil
subject: Viscosity
subject: mass diffusion

description: Employing CO2 as the non-condensable gas in the Vapex process is an attractive option. The high solubility and viscosity reduction potential of CO2 could provide improvement to Vapex performance. Mixtures of CO2 and a hydrocarbon such as propane allow the solvent to be tailored to different reservoir conditions. To select the optimum solvent mixtures, data on the phase behavior and physical properties of the oil-solvent system are required. The saturation pressure and solubility of propane in Athabasca bitumen as well as the liquid phase densities and viscosities, were measured at temperatures from 10 to 50°C. The solubility of pure carbon dioxide in Athabasca bitumen was measured and compared with the literature data. Two liquid phases were observed at carbon dioxide contents above approximately 12 wt%. A correlation based on Henry’s law was found to fit the saturation pressures at carbon dioxide contents below 12 wt%. The saturation pressure and solubility of carbon dioxide and propane in Athabasca bitumen, as well as the liquid phase densities and viscosities, were measured for three ternary mixtures at temperatures from 10 to 25°C. Two liquid phases (carbon dioxide rich and bitumen rich) were observed at 13 wt% carbon dioxide and 19 wt% propane. Only liquid and vapour-liquid regions were observed for the other two mixtures:13.5 wt% propane and 11.0 wt% carbon dioxide; 24.0 wt% propane and 6.2 wt% carbon dioxide. Vapex physical model experiments were conducted using a fixed composition of the CO2 and propane binary mixture as the solvent. The objective of this work was to evaluate the performance of this solvent in recovering Athabasca bitumen. In-line measurements of the density and viscosity of the produced oil were used to gain further insight into the mechanisms involved in the process. An improved mathematical model was developed to predict the oil recovery performance of Vapex process. The compositional dependence of diffusion coefficient causes a strong non-linearity in the moving boundary diffusion equation of the Vapex mathematical model. Pseudo-concentration and pseudo-time terms were defined to resolve this non-linearity. The concentration profile ahead of solvent-bitumen interface was obtained analytically using the HIM “Heat Integral Method”. This results in a new correlation for the “average flow fraction of the heavy oil” in the flowing mixture, and drainage rate of heavy oil. The new correlation for drainage rate of heavy oil has the same square-root relationship to most of the key reservoir parameters as the previous theories except that its relationship to kinematic viscosity is altered by the concentration dependence of the diffusion coefficient. The new mathematical model was tested against our Vapex experimental results at a pseudo steady state condition to back calculate the solvent apparent mass diffusion coefficient at the vapor chamber interface and its power law functionality to solvent concentration.