EFFECT OF ASPHALTENE DEPOSITION ON THE VAPEX PROCESS - A PRELIMINARY INVESTIGATION USING A HELE-SHAW CELL

Recovery using vapourized hydrocarbon solvents near their dew points, termed ''Vapex'' (vapour extraction), is emerging as a possible alternative to the inefficient thermal processes currently in use for the recovery of the huge reserves of heavy oil and bitumen. In this new process, solvent dilutes the highly viscous heavy oil and bitumen and aids the flow by reducing viscosity. Propane and ethane are considered to be the most suitable solvents for the process. However, a mixture of butane, propane and ethane can also be used, depending on the prevailing pressure in the reservoir. Oil is produced by gravity drainage to horizontal wells. One important advantage of this approach can be the in situ upgrading of heavy oil by deasphalting; this can make the produced crude comparable to lighter oils in quality. Moreover, elimination of the undesirable asphaltenes from the crude can solve several down stream problems. When sufficient solvent is employed to produce deasphalting, one important question is - ''Do the deposited asphaltenes plug the reservoir and affect the flow of diluted oil?'' An investigation, carried out in a Hele-Shaw cell using propane and several heavy crudes that concluded that asphaltene deposition does not prevent the flow of oil through the reservoir for the proposed production scheme, is described in the present paper. It has been observed that deasphalting takes place if the injected propane pressure is close to or higher than the vapour pressure of propane at the same temperature. The mechanism of the associated process is studied and described. In another set of experiments in the Hele-Shaw cell, the drainage profiles of heavy oil and bitumen (solvent bitumen interface) in the presence of propane were studied. These were used to estimate the hypothetical ''Vapex parameter'' that combines the effect of viscosity, diffusivity, density and solvent concentration along with reservoir parameters, formulated from the model developed by Butler and Mokrys(18). This parameter was used to scale the results for prediction of field flow rates. A comparison of this parameter for crudes of different reserves gives the relative rates of production from these reservoirs.