Abstract

This paper presents an experimental and theoretical study of bitumen/heavy oil mobilization by solvent, gases and surfactants under cold conditions. Experimental runs employing a high permeability channel were conducted in a rectangular model which allowed packing of a bottom water zone. Runs made with this model showed strong dependence on solvent slug size, thickness and permeability of the water zone. Small solvent slug sizes were not efficient for recovering the highly viscous oil. Most of the solvent was entrained in the Formation and failed to reach the production well. Stimulation of oil sands by the carbon dioxide and surfactant in combination with solvent did increase the incremental recovery of the bitumen and the injected solvent. Combination of gas and surfactant were nor effective in the absence of a solvent. A thin bottom water zone enhanced the injectivity and interwell communication. Although the thinner the water zone, the higher the recovery, very high injection pressures were required for very thin water zones.

A simulator for solvent leaching of oils sands was extended to include a number of additional effects. The efficiency of the teaching process was found to be dependent on the mass flow rate, slug size, location of injection and production points, relative thickness and permeability of the water zone. Simulation runs were compared with the experimental results and good matches were obtained. It was shown that a thin bottom water zone is helpful in obtaining initial injectivity, yet not detrimental to bitumen recovery. Bitumen-to-water zone ratio of about 5 gave optimal recoveries. From the concentration profiles it was observed that the bottom water served as a transport layer for the dissolved bitumen. The leaching process eventually (1.5 HCPV injected) became very inefficient, as signified by the sharp drop in the bitumen concentration in the effluent. The dissolved bitumen is transported by miscible displacement. As much as 85% of bitumen and 68% of solvent were recovered in such a solvent leaching process.

Introduction

Conventional oil recovery methods cannot be used directly in bitumen saturated oil sands because of the very low bitumen mobility. Thermal methods are often applied as a means to exploit such reservoirs, with limited success In some instances, use of additives may help mobilize the bitumen. Additives such as caustic, foam, polymers, surfactants, solvents, gases might increase mobility, reduce interfacial tension and residual oil. Aliterature survey reveals that weir use is usually associated with a thermal recovery scheme. Because of me high cost of these additives and the low oil price, a careful screening of these additives is imperative to make any project economically feasible.

Previous work concerning heavy oil/bitumen is relatively new and limited. Most of the work was done at the laboratory scale and has not been field-tested.

Previous Work

The use of solvents with steam or alone has been reported in the literature. Alikhan and Farouq Ali1,2 studied the effects of solvent slug size, steam slug, hot water, and injection rates on the recovery of heavy oil in a Linear core packed with glass beads.

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