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Summary. This is one of three companion papers describing a micellar/polymer or chemical flood simulator and comparing its results to experimental data. Various physical-property models required by chemical flood simulators have been improved and others developed. The most significant development is the use of pseudophases to model phase behavior. The method allows representation of four pseudocomponents. This is made possible by assuming that alcohol is distributed among the other three pseudocomponents, thus forming three pseudophases that are assumed to be in thermodynamic equilibrium. Another improvement relates to the ion-exchange model. Cations are considered to exchange with both surfactant micelles and clays. The model assumes the exchange to be entirely a result of electrostatic association. A model for treating physical dispersion coefficients as a function of saturations has been physical dispersion coefficients as a function of saturations has been added. The model is based on experimental evidence and is purely empirical.

Introduction

Phase behavior of multicomponent mixtures is difficult to Phase behavior of multicomponent mixtures is difficult to represent geometrically, let alone describe mathematically. Geometric representations are limited by three-dimensional (3D) space. The maximum number of components that can possibly be represented is four, because this corresponds to three independent components. Micellar/polymer processes, however, often involve mixtures with more than four components. Geometric representations of such mixtures are possible only if pseudocomponents are defined so that the maximum number of pseudocomponents is four. This reduced form is acceptable if any mixture of the pure components can also be represented by a mixture of the pseudocomponents, Phase behavior of microemulsions has been represented on pseudoternaries by many authors. These pseudotenaries generally lump the pseudoternaries by many authors. These pseudotenaries generally lump the surfactant and alcohol as one pseudocomponent and assume that any phase of multiphase mixtures contains the same ratio of surfactant to alcohol so that these phases can be represented on the same diagram. This assumption, however, is not accurate for all the surfactant formulations use in oil recovery. Wickert et al . and Salter point out that choosing pseudocomponents arbitrarily can cause problems. Francis discusses problems that can arise when linear algebraic techniques are used to select pseudocom-ponents. Vinatieri and Flemings discuss a criterion for choosing pseudocom-ponents. Vinatieri and Flemings discuss a criterion for choosing pseudocomponents that is based on regression analysis. pseudocomponents that is based on regression analysis. In this paper, it is assumed that surfactant mixtures can be represented by four pseudocomponents: brine, alcohol, sulfonate, anoil. A theoretical basis that makes use of the pseudophase equilibrium idea is used to represent a mixture of these four pseudocomponents by a reduced system of three pseudocomponents. pseudocomponents by a reduced system of three pseudocomponents. These three pseudocomponents are brine plus alcohol, oil plus alcohol, and surfactant plus alcohol. In contrast to previous representations, the distribution of the alcohol is variable with total composition. so infinitely variable pseudotenaries are used rather than a single fixed pseudotenary. The effect of the alcohol and divalent ions on the optimal salinity is modeled by use of Hirasaki's relation.

The dependence of phase behavior on divalent ion concentration makes it important to model those concentrations in the free state and in association with clays and surfactant. A cation exchange model based on electric association is used, where the exchange of monovalent and divalent cations with both clays and micelles is considered.

Phase Behavior Model Phase Behavior Model The phase behavior is characterized by four pseudocomponents: surfactant, alcohol, oil, and brine. The model is based on the pseudophase equilibrium idea, which assumes that microemulsion phase can be pseudophase equilibrium idea, which assumes that microemulsion phase can be represented by three pseudophases. These are an oil-rich phase, a brine-rich phase, and a surfactant-rich phase. The model phase, a brine-rich phase, and a surfactant-rich phase. The model neglects any surfactant in the oil and brine phases and assumes that the oil and brine pseudophases are of the same composition as the excess-oil and excess-brine phases, respectively. This representation is depicted schematically in Fig. 1. The alcohol is considered to he distributed among the three pseudophases. Constant alcohol partition coefficients are used. The pseudophases are used as the partition coefficients are used. The pseudophases are used as the pseudocomponents for a pseudotenary representation to calculate pseudocomponents for a pseudotenary representation to calculate phase compositions and volume fractions. phase compositions and volume fractions. Consider an overall composition P(C1, C2, C3, C7), as shown in Fig. 2. From an alcohol material balance applied to the three pseudophases, we can write pseudophases, we can write (1)

With constant partition coefficients defined as

(2a)

(2b)

Eq. 1 can be expressed as

from which

(3)

Eqs. 2 and 3 can be used to calculate the composition of the pseudophases, which are represented by the apexes of the pseudophases, which are represented by the apexes of the pseudoternary slice in Fig. 2. pseudoternary slice in Fig. 2. SPERE

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