Abstract

This paper deals with the displacement of oil under tertiary conditions, by micellar solutions derived from the same phase diagram but having a different oil and water content.

The phase diagram is a Winsor's type I system-microemulsions along the binodal curve are in equilibrium with nearly pure excess oil. A very thorough investigation of the phase behavior was made and some of the properties were measured, such as specific gravities, viscosities, interfacial tensions and alcohol distribution.

Floods were performed at reservoir rates by using micellar slugs having different sizes and compositions. Several aspects of displacement flow behavior were studied by extensive analysis of the core effluents and local residual oil saturation and sulfonate retention measurements.

The interpretation of the results is approached from the angle of phase behavior and the petrophysical properties of the rock. The conditions of oil removal properties of the rock. The conditions of oil removal and entrapment are investigated in the transition zones where sulfonate concentration changes take place. The great extent of these zones excludes piston-like displacement as a schematic representation of the process. In other respects, the oil bank characteristics are not in agreement with the values calculated from relative permeability curves and fluid mobilities. permeability curves and fluid mobilities

Introduction

It is now well established that, in field application of micellar solutions where, from economical considerations, injected volumes are much lower than the pore volume to be swept, micellar polymer flooding is, for the main part, an immiscible process. This clearly appears with aqueous solutions of surfactants, but can also be applied to microemulsions, though the process is, at the time, a temporarily and locally process is, at the time, a temporarily and locally miscible displacement.

The main consequence of this analysis based on theoretical and experimental considerations is that, from the different mechanisms which control the displacement of oil, the one which acts on viscous and capillary forces, plays an important role in the release of oil. This idea is enclosed in the dimensionless concept of capillary number, representing the viscous capillary forces ratio, many expressions of which have been proposed in the literature.

Many authors apply themselves to search for low interfacial tension systems and specify the relations between variables and properties in order to determine the optimization rules of micellar solutions. Similar behavior has been found for dilute aqueous solutions of surfactants and microemulsions and these studies revealed that an optimal value exists for each parameter, salinity, alcohol molecular weight or temperature for which the interfacial tension or (and) the concentration of the amphiphile compounds are minimal.

No other valuable approach consists in studying how an oil-water-surfactant and alcohol system separates after the thermodynamic equilibrium is attained. A classification in four types is deduced from the phase behavior: a system containing a microemulsion in equilibrium with oil, a microemulsion-water system, an intermediate system made of a microemulsion with water and oil in excess, and finally a one phase system corresponding to a complete solubilization of oil and water. These trends lead to three theoretical phase diagrams called Winsor's type I, II and III, according to the nature of the phases in the polyphasic zone. The type of diagram is affected by changing the salinity, the temperature, the oil composition, the cosurfactant molecular weight or the surfactant hydrophile-lipophile balance. From these experimental observations, many investigators introduced the concept of solubility parameter and demonstrated the correlation between interfacial properties, solubilization effects and phase behavior. These correlations are very useful for defining a methodology for the optimization of micellar systems in fundamental research as well as in field applications.

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