Emulsification of Water Into Bitumen In Co-injection Experiments
Authors: Chen T. , Yuan J.Y. , Serres A.J. , Rancier D.G. 
Published: March 2010

Co-injection of water and bitumen into sand packs has been conducted to study the flow of emulsions in porous media. It was found that the most important factor in the formation of emulsions is the wettability of the medium. An oil wet medium is more favourable for emulsification than a corresponding water wet one. When the wettability of the sand pack is not changed, the degree of emulsification increases as the flow rate of water increases.

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

Introduction

Recently, Vittoratos(1) identified that a production cycle in Imperial Oil Resources Limited (IORL)'s cyclic steam stimulation (CSS) operation in Cold Lake can be classified into a number of stages, one of which is production of a single phase emulsion. He also argued that it was formed in situ, and flowed through the porous media to the well bore. Based on the produced fluid samples it is a water-in-oil emulsion 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 the flow of emulsions in porous media.

Bennion et al.(2) 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 an emulsion is a thermodynamically unstable entity, and that, inside the undisturbed reservoir, water and bitumen have had geological time to phase separate, it is very likely that initially the two phases are separated. The produced bitumen, however, is always in the form of emulsion(3). At some stage of movement of water and bitumen from their initial state to the well head, emulsification must take place. It is possible that it could take place at the perforations. If, however, we accept Vittoratos'(1) argument that emulsions are actually formed in the reservoir, then emulsification must occurr 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 this system. Later, it became apparent that the wettability of the sand pack was the most important factor in causing emulsification to occur.