Rate Dependence Of Micellar Emulsion Displacement And Anomalies Due To X-Ray Shadowgraphy Analysis
Authors: Soremi A. , Bennion D.W. 
Published: March 2010

Abstract
A study was undertaken to determine why there is a wide variation in reported breakthrough sweep efficiencies for miscible displacement, especially when X-ray shadow graphy is used for the detection of breakthrough in 1/4 five-spot models. This anomaly was found to be due to the difficulty of observing breakthrough when scattering of X-rays occurs. Breakthrough was detected at about the same time as it was with the conventional Talra-ctive index method, after modifications were made in the hybrid computed programs and the X-ray signals were passed through an electronic filter to video analysis. The breakthrough sweep efficiencies obtained by this method were compared to generally accepted values and found to be in good agreement. Size was not found to be a factor in this anomaly.
In view of the non-Newtonian behaviour of micellar emulsions, the influence of displacement rate on breakthrough sweep efficiency 'was also studied. However, the pressure limitations of the sandstone samples used prevented the use of high injection rates or highly viscous micellar emulsions.

Introduction
THERE HAVE BEEN SEVERAL INVESTIGATIONS into the influence of mobility ratio on areal sweep efficiency at breakthrough in miscible displacement. A paper by Haberman(1) summarizes the results of most of these investigations. The analytic means used for monitoring fluid flow varied from X-ray shadowgraphy(2,3) to colour photography(l) and potentiometry(4). The potentiometric and X-ray shadowgraphy results show a large deviation from other results, especially at very favourable mobility ratios where there is no instability or ‘fingering’ at the front to make measurements of swept area difficult. The explanation offered by Haberman is that the anomaly might be due to the method or means of measuring sweep efficiency. Despite this anomaly, the X-ray shadowgraphy is widely used because it has an advantage over all others in being able to monitor flood fronts through opaque porous media.
In has already been established that micellar emulsions are non-Newtonian(5). For locally and completely miscible fluids such as those used by Durrani(6) injection rate has no appreciable influence. This same conclusion was reached by Healy et al. (7) for low-viscosity micro-emulsions as long as slug breakdown does not occur.
The objectives of this study were to investigate the reasons for excessive deviations in breakthrough sweep obtained by X-ray shadowgraphy and to correct the problem. Also, a study of the variation of breakthrough sweep of micellar emulsion with rate was carried out.

Experimental Procedure and Technique

Emulsion Flooding

Equipment and Procedures
A schematic diagram of the equipment is shown in Figure 1. For this experiment, the foam-generating equipment was not used. The sandstones were saturated with the oil phase by creating a vacuum in the model with a vacuum pump. Oil phase of the desired viscosity and! or density was obtained by mixing the appropriate proportion of the refined oils (Soltrol 130, Protol and Kaydol) with n-butyl iodide, a radio-opaque fluid. Micellar emulsions with compositions as listed in Table 1 were placed in polyethylene bags which separated the hydraulic oil from the emulsion inside the hydraulic accumulator.