Effect of Asphaltene Deposition On the Vapex Process: A Preliminary Investigation Using a Hele-Shaw Cell
Authors: Das S.K. , Butler R.M. 
Published: March 2010

Recovery using vaporized 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 mast 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 downstream problems.

When sufficient solvent is employed to produce deasphalting, one important question is - "Do the deposited asphalteoes 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 vapor 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 arid 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.

Introduction

With the decline of conventional oil reserves, a major thrust of oil industries throughout the world is on the exploitation of heavy oil and bitumen reserves. The amount of this crude oil reserve is twice as much as that of the conventional oil reserves(1). The estimated OOIP of heavy oil in Canada is 400 billion m3 (2), which is twice that of the total conventional oil reserves of all Gulf countries. Alberta in particular is very rich in heavy oil and tar sand deposits, the total estimated reserve being 1.6 trillion barrels buried at a depth of 0-800 m, although only 5% of this reserve is recoverable by open pit mining from shallow reservoirs(3).

FIGURE 1: Effect of solvent concentration and temperature on bitumen viscosity. (Available in full paper)

In most cases, conventional recovery techniques cannot be implemented in the heavy oil and bitumen reservoirs due to the very high viscosity of the oil.