Abstract

Co-injection of water and bitumen into sand packs have been conducted to study the flow of emulsion in porous media. It was found that the most important factor in the formation of emulsion is the wettability of the medium. An oil wet medium is more favorable for emulsification than a correspondent water wet one. When the wettability of the sand pack was not changed, the degree of emulsification is ependent on the flow rate of water, being higher at higher rates.

Considering that the initial state of the Clearwater ormation in Cold Lake is water wet, and that it may have changed over to oil wet state during the course of cyclic steam stimulation operation, the emulsification condition may be changed correspondingly. This change should have a strong impact on productivity as well. It is therefore very important to understand the effect of wettability on emulsification.

Introduction

Recently, Vittoratos1 identified that a production cycle in Imperial Oil Resources Limited (lORL)'s cyclic steam timulation (CSS) operation in Cold Lake can be classified into a number of stages, one of which being a single phase emulsion production. He also argued that it was formed insitu, nd flowed through the porous media to the well bore ased on the produced fluid samples it is a water-in-oil mulsion which has a higher viscosity than bitumen. The implication of this high viscosity is that it might reduce the rate of bitumen recovery. It is, therefore, important to study he flow of emulsion in porous media.

Bennion et al2 performed a number of co-injection experiments with bitumen taken from an unspecified field and produced water into preserved core samples from the same field. Their results indicated that emulsion was produced in the co-injection experiments. The water volume fractions in the produced emulsion were between 0.1 and 0.2 at different flowing fractions.

Considering that emulsion is a thermodynamically unstable entity, and that inside the undisturbed reservoir water and bitumen have geological time to phase separate, it is very likely that the initial state of the two are separated. The produced bitumen, however is always in the form of emulsion3. At some stage of movement of water and bitumen from their initial state to the well head, emulsification must have taken place. There are some believes that it could have taken place at the perforations. If, however, we accept Vittoratos1 argument that emulsions are actually formed in the reservoir, then emulsification must have occurred during flow of the separated phases into the well bore. It is under these assumptions that we designed co-injection experiments to study the factors causing emulsification.

Initially we were quite surprised that the measured volume fraction of water in the produced emulsion from these experiments was much lower than field observations. In fact for most of the experiments, the level of emulsification was so low that it was quite obvious that a single phase emulsion flow assumption as envisaged by Vittoratos, was definitely not applicable to describe the system.

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