Mechanism of the vapor extraction process for heavy oil and bitumen

The vapor extraction process may be suitable for the recovery of huge resources available in the form of highly viscous heavy oil and bitumen. Vaporized hydrocarbon solvents are used to reduce the viscosity; the diluted oil drains by gravity. Low energy consumption, less environmental pollution, in situ upgrading, lower capital costs, etc., make the process superior to the currently used thermal processes. Experiments were carried out in a Hele-Shaw cell and in a scaled packed cell to evaluate the performance of this process and study the mechanism. The experimental results showed that in porous media, the process performs as much as an order of magnitude better than expected from typical calculation using molecular diffusivity alone. In porous media, the process takes place in a contact zone. In this zone, the high-viscosity oil contacts the solvent vapor in the fine capillaries that offer a higher interfacial area of contact. The process involves transient diffusion of solvent into the bitumen at the interface. As soon as the oil at the interface attains mobility due to viscosity reduction, it drains, exposing a new interface of bitumen having a very low concentration of solvent. Surface renewal, aided by capillary imbibition, yields a higher mass transfer rate that enhances the rate of extraction. (C) 1998 Elsevier Science B.V. All rights reserved.