Applicability of CO2-Based Vapex Process to Recover Athabasca Bitumen

Abstract

Abstract Employing CO2 as the non-condensable gas in the Vapex process is an attractive option that could provide environmental benefits of CO2 sequestration along with improved Vapex performance. Mixtures of CO2 and a hydrocarbon such as propane allow the solvent to be tailored to different reservoir conditions. To test potential solvent mixtures, the phase behavior and physical properties and physical model experiments are required. We have previously reported on the phase behavior, viscosity and density of the CO2-propane-Athabasca Bitumen systems (Badamchizadeh et al., 2008a,b). These results confirmed the ability of carbon dioxide and propane mixtures to sufficiently reduce Athabasca bitumen viscosity and were used to design the solvent compositions utilized in the physical model tests reported here. The experimental approach used in these tests was to use a fixed composition of the CO2 and propane mixture as the Vapex solvent. The objective of this work was to evaluate the performance of this solvent in recovering the Athabasca bitumen. The experiments were carried out at room temperature in a physical model. 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. Introduction The growing demand for the energy along with limited conventional oil reserves in the world has stimulated the pursuit of other hydrocarbon resources such as heavy oil and bitumen. Heavy oil is distinguished from conventional oils by its high density (above 960 kg/m3) and high viscosity (typically above 12000 cp) (Farouq Ali 2000). The world total estimated original oil in place (OOIP) in heavy oil and bitumen forms is approximately 6 trillion bbl. Major parts of these resources are in Canada (~36%) and Venezuela (~27%). (Janish, A., 1981) Thermal methods have been successfully applied to a number of heavy oil reservoirs but are energy and water intensive. Among several alternate methods for heavy oil and bitumen recovery, solvent extraction of the heavy oil deposits has received considerable attention (Das, 1995; Jiang, 1997, Talbi and Maini, 2003, Okazawa, 2007). Butler and Mokrys (1989) conceived the "Vapor Extraction" (Vapex) method as a solvent analogue of the steam assisted gravity drainage (SAGD) process. The Vapex process usually involves two horizontal wells, with an injection well located directly above the production well. The vaporized solvents are injected through the injection well and a chamber of solvent vapour forms around the well, as shown in Figure 1. At the walls of the chamber, the solvent dissolves into a surface layer of the heavy oil and dramatically reduces its viscosity. The diluted oil layer becomes sufficiently mobile to drain down under the influence of gravity into the production well located near the bottom of the formation. It is then pumped out to the surface and the vapor chamber grows laterally as more oil is drained out of the reservoir.