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Summary In this paper, we compare numerical simulations made with our previously reported simulator with both our own and literature experiments. The most significant improvement concerns the phase behavior model used in the simulator. The new model approximately represents the phase behavior of pseudoquaternary mixtures containing surfactant, cosurfactant, oil, and brine. The different effects of sodium and calcium cations in the mixtures are accounted for with a new cation exchange model allowing for exchange with both clays and micelles. A tertiary oilflood experiment is reported that includes a more complete analysis of phase compositions and properties than generally available previously. Produced samples were analyzed for surfactant, alcohol, sodium, calcium, polymer, tritium, water, carbon-14-tagged decane, and decane. These analyses and pressure drop were compared with simulated behavior. Supporting physical property data were used as much as possible to estimate simulator property data were used as much as possible to estimate simulator input parameters rather than adjusting or "history matching" the results. Agreement with the most important features of the experiment was good. This agreement and good agreement with an experiment from the literature lead us to conclude that a significant improvement over previous efforts has been achieved. Especially noteworthy is our previous efforts has been achieved. Especially noteworthy is our capability to account for the chromatographic separation of surfactant and alcohol. Introduction We have had a program for several years to investigate systematically the phenomena needed for compositional simulation of the micellar/polymer process. Several comparisons of laboratory coreflood experiments with micellar/polymer or chemical flood simulators have been reported. Although significant progress has been made, these efforts have been limited by the lack of complete experimental data for even one system and by the incompleteness or inaccuracy of numerous physical property models used in the simulators. Although significant uncertainties remain in some aspects, especially regarding three-phase relative permeability and dispersion, Which continue to be investigated, permeability and dispersion, Which continue to be investigated, the treatment of several other phenomena has been significantly improved, resulting in much better agreement with oil recovery experiments. In this paper, we emphasize the application of the two most important improvements: the phase behavior and cation exchange of sodium and calcium with micelles. One of our most recent and complete oil recovery experiments is briefly reported here. Camilleri and Lin have reported more details and other experiments, and more comparisons with our simulator can be found in these and Refs. 4 and 17. We also compare our simulations with an experiment of Gupta, one of the most completely reported experiments in the literature, which has been previously analyzed and serves as a good illustration of the separation of alcohol and sulfonate in the core. Alcohols are often used as cosolvents or cosurfactants in surfactant formulations to improve the phase behavior. They can prevent or minimize gels, emulsions, liquid crystals, precipitation, prevent or minimize gels, emulsions, liquid crystals, precipitation, and polymer/surfactant interaction. They can also decrease surfactant retention, alter the optimum salinity, and increase the size of the active region. The integrity of surfactant slugs containing alcohol used for oil recovery therefore depends on the relative transport of the surfactant and alcohol. An obvious but difficult objective is to design the chemical flood so that the surfactant and alcohol will transport without separation. This is promoted by close association of alcohol and surfactant and by situations that minimize selective partitioning and adsorption. Both our theoretical understanding of these partitioning and adsorption. Both our theoretical understanding of these phenomena and our capability to simulate them have been limited phenomena and our capability to simulate them have been limited in the past. For this reason a more generalized phase behavior model was developed based on the pseudophase theory, which assumes principally that the compositions of brine and oil in the principally that the compositions of brine and oil in the microemulsion phase are identical to those of the excess brine and excess oil, respectively. In particular, the alcohol content is the same for a given pseudophase, although different for brine, oil, and membrane pseudophases. The last refers to the surfactant or interfacial region.

A thermodynamic model is presented for modeling the partitioning of amphiphilic species between the different partitioning of amphiphilic species between the different phases of systems typically used for chemical flooding. phases of systems typically used for chemical flooding. The model, an extension of the pseudophase model by Biais et al. that can analyze only a four-component system, can work with five-component systems, including two partitioning amphiphilic species (e.g., two alcohols or one alcohol and a partitioning cosurfactant species). The self-association of alcohol in the organic phases, which results in a variable alcohol partition coefficient, is considered. Experiments to determine thermodynamic constants (which are entered into the model) are described for four-component systems, including one alcohol. The salinity dependence of these parameters is also studied. Brine/decane/isobutanol/TRS 10–410 as well as brine/nonane/ isopropanol/TRS 10–80 systems are considered. Some computations of pseudophase compositions for the five-component model and for various overall compositions are included. This partitioning model has been included in the chemical-flooding simulator developed at the U. of Texas; the results of this model have been presented in another paper. The model used for the presented in another paper. The model used for the binodal surface that is required to calculate phase compositions from pseudophase compositions is presented in this paper, as well as comparisons with experimental data for both four- and five-component systems. Reservoir simulation results are presented in Ref. 3. Introduction The possibility of reaching very low interfacial tensions (IFT) during the displacement of oil by surfactant solutions has been the subject of intense interest for some time. Because the decrease in IFT can be as much as several orders of magnitude, almost all the contacted oil can be mobilized by this process. However, the recovery rate has proved to be very sensitive to many parameters, and the process has to be designed carefully to achieve a good oil recovery. It is commonly recognized that the phase behavior is one of the most critical features for the phase behavior is one of the most critical features for the design of chemical oil-recovery processes. Many investigators have studied phase behavior of systems with various combinations of brine, oil, surfactants, and cosurfactants. Winsor introduced a very convenient classification of phase behavior for such systems. Type I is a lower-phase microemulsion (surfactant-rich phase) in equilibrium with an oleic phase; Type II is an phase) in equilibrium with an oleic phase; Type II is an upper-phase microemulsion in equilibrium with an aqueous phase, and Type III corresponds to a middle-phase microemulsion in equilibrium with both aqueous lower phase and oleic upper phase. The number of phases and their composition determined IFT's, viscosity, relative permeabilities and other hydrodynamic parameters on permeabilities and other hydrodynamic parameters on which the efficiency of the process is directly dependent. Components present in the reservoir during chemical flooding include water, electrolytes, oil, polymer, and the amphiphilic species surfactant and cosurfactant. From the viewpoint of chemical thermodynamics, the number of chemical species is very large if we consider every species of which oil, surfactant, and cosurfactant are made. Fortunately, some of these species behave collectively, so they can be considered a single pseudocomponent in the phase behavior description, thereby pseudocomponent in the phase behavior description, thereby making the study more tractable. For example, Vinatieri and Fleming considered brine a good pseudocomponent, which means that the ratio of salt to water is about the same in each phase. McQuigg et al.'s experiments yield similar conclusions. Even crude oil has been shown to be a good pseudocomponent with a fairly acceptable accuracy. Dealing with amphiphilic species is far more difficult. In some laboratory studies, surfactant can be a chemically pure component, but for field applications it is usually a complex blend, such as petroleum sulfonates. In the case of petroleum sulfonates, different monosulfonated or polysulfonated species are present with varied carbon polysulfonated species are present with varied carbon tails. Commercial nonionic surfactants, which generally are ethoxylated alcohols, show a broad distribution of ethylene oxide number (EON). In both cases, investigators have shown that these commercially available surfactants do not behave collectively but in some situations partition selectively between the phases. The cosurfactant generally is an alcohol or an ethoxylated alcohol. Although many research programs currently are devoted to the design of alcohol-free systems to avoid some of the drawbacks induced by its presence (lower solubilization parameters, higher IFT's), most of the commonly used systems include alcohol or even a blend of alcohols with different carbon chain lengths and/or branching. SPEJ P. 693

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. 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. 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. pseudoternary slice in Fig. SPERE P. 433

In order to test the effectiveness of complexing agents for in-depth cross-linking and mobility control in polymer and waterfloods, we investigated the transport of aluminum citrate solutions in sandstone and limestone cores. The study was prompted by experimental observations indicating that crosslinking attempts cause plugging of the inlet end of core sections unless special precautions were observed. The plugging was caused by poor transport of the aluminum citrate solutions, which, in turn, was caused by precipitation of aluminum hydroxide in limestone cores, and of both aluminum and ferric hydroxide in sandstone cores. The formation of these precipitates, and the poor transport of the aluminum citrate solution was confirmed experimentally and modeled quantitatively by a geochemical flow simulator. We then used the flow simulator to design injected solutions that would avoid precipitation, generally by raising the injected pH and by using a larger citrate to aluminum ratio. By using these solutions the precipitation could be avoided, and the aluminum citrate could be transported in an unretarded fashion. Polymer cross-linking treatments using solutions designed to eliminate precipitation generally showed more uniform mobility reduction, and an absence of the plugging observed in the first set of flow experiments.