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 bitume n. Vaporized hydrocarbon solvents are used to reduce the viscosity; th e diluted oil drains by gravity. Low energy consumption, less environm ental pollution, in situ upgrading, lower capital costs, etc., make th e process superior to the currently used thermal processes. Experiment s 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 ca lculation using molecular diffusivity alone. In porous media, the proc ess takes place in a contact zone. In this zone, the high-viscosity oi l contacts the solvent vapor in the fine capillaries that offer a high er interfacial area of contact. The process involves transient diffusi on 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 o f solvent. Surface renewal, aided by capillary imbibition, yields a hi gher mass transfer rate that enhances the rate of extraction. (C) 1998 Elsevier Science B.V. All rights reserved.