Numerical Simulation and Experimental Verification of Oil Recovery by Macroemulsion Floods
Authors: Khambharatana F. , Thomas S. , Ali S.M. Farouq 
Published: December 2007

The importance and application of emulsions in the oil recovery has received considerable attention; for example, emulsion flooding which is a complex EOR process involving several mechanisms that occur at the same time during displacement. Therefore, to simulate oil recovery by emulsion flooding requires an understanding of the flow mechanics of emulsions in porous media. With this end in view, the present study was carried out to achieve a better mechanistic understanding of emulsion flow and its mathematical representation. Particularly, emulsion rheology and droplet capture for the system of comparable drop and pore sizes were investigated comprehensively. These mechanisms, namely emulsion rheology, droplet capture, and surfactant adsorption, were then represented mathematically and incorporated into a one-dimensional, three phase (oleic, aqueous, and emulsion) mathematical model which accounted for interactions of surfactant, oil, water, and the rock matrix.

The simulator was validated by comparing the simulation results with the results from linear core floods performed in the laboratory. The comparison was made using different physical property models and testing various mechanisms to determine which combination best followed the core flood observations and measurements. It was found that a multiphase non-Newtonian rheological model of an emulsion with interfacial tension-dependent relative permeabilities and time-dependent capture gave the best match of the experimental core floods. A sensitivity study of the injection pressure and cumulative oleic recovery was also carried out to determine the effect of the process variables on the model predictions.

Introduction

Since emulsions play an important role in many EOR processes, attempts have been made to simulate these processes with increasingly complex compositional simulators. These require a detailed understanding of the mechanisms involved during the displacement process. Therefore, there is a need to understand the physics controlling the flow of an emulsion in a porous medium. However, very little research has been carried out in the area of the flow mechanics of emulsions in porous media. Additionally, emulsion rheology and drop capture have been investigated separately for certain conditions. These conditions restrict the model to specific applications. This leads to the question of how emulsion transport occurs in a porous medium in the case where emulsion drop size and the pore size are comparable, which is often the case. Therefore, the present study investigates these subjects to achieve a better mechanistic understanding of emulsion flow and its mathematical representation. This will provide information that can be applied in any EOR process involving emulsion flow.

Experimental Work

Physical Mechanism Observations. A number of experimental core floods were conducted in this study to observe the physical mechanisms that occurred during stable emulsion flow in a porous medium. These are described in Ref. 1. The observations found from this study can be summarized as follows:Observations were made of the rheological behaviour of the caustic and surfactant emulsions for the system of comparable drop to pore size for both Berea sandstones and Ottawa sand packs. Rheological similarities were seen when the emulsions flowed in porous media and in a viscometer with slight differences probably due to an interaction between drops and pores.The above finding of the emulsion rheology was drawn from the comparison of the rheological behaviour of emulsion flow in a porous medium with the rheological behaviour of an injected emulsion as measured by a viscometer.