Surfactant formulations for enhanced

During the past decade, it has been reported that many surfactant formulations for enhanced oil recovery generally form multiphase microemulsions (18-20). From these studies, it is evident... 

Solubllization. The effectiveness of surfactant formulations for enhanced oil recovery depends on the magnitude of solubilization. 

Phase Behavior. The surfactant formulations for enhanced oil recovery consist of surfactant, alcohol and brine with or without added oil. As the alcohol and surfactant are added to equal volumes of oil and brine, the surfactant partitioning between oil and brine phases depends on the relative solubilities of the surfactant in each phase. If most of the surfactant remains in the brine phase, the system becomes two phases, and the aqueous phase consists of micelles or oil-in-water microemulsions depending upon the amount of oil solubilized. If most of the surfactant remains in the oil phase, a two-phase system is formed with reversed micelles or the water-in-oil microemulsion in equilibrium with an aqueous phase. 

The phase behavior of surfactant formulations for enhanced oil recovery is also affected by the oil solubilization capacity of the mixed micelles of surfactant and alcohol. For low-surfactant systems, the surfactant concentration in oil phase changes considerably near the phase inversion point. The experimental value of partition coefficient is near unity at the phase inversion point (28). The phase inversion also occurs at the partition coefficient near unity in the high-surfactant concentration systems (31). Similar results were also reported by previous investigators (43) for pure alkyl benzene sulfonate systems. 

The effectiveness of surfactant formulations for enhanced oil recovery depends on the magnitude of solubilization. By injecting a chemical slug of complete miscibility with both oil and brine present in the reservoir, 100% recovery of oil should be possible. 

The phase behavior of surfactant formulations for enhanced oil recovery is also affected by the oil solubilization capacity of the mixed micelles of surfactant and alcohol. For low concentration surfactant systems, the surfactant concentration in the oil phase changes considerably near the phase inversion point. 

We have recently reported (6, 7) that those surfactant formulations which yield good oil recovery exhibit both low interfacial tensions and low interfacial viscosities. Our experiments have shown that surfactant formulations which ensure low interfacial viscosity will promote the coalescence of oil droplets and thereby decrease the emulsion stability, thus enhancing the formation of a continuous oil bank. It has been demonstrated that the requirements for emulsion stability are the presence of an interfacial film of high viscosity and a film of considerable thickness. We have observed that the surfactant concentration which minimizes the interfacial tension may not simultaneously minimize the interfacial viscosity. Hence, our results indicate both interfacial tension and interfacial rheology must be considered in selecting surfactant formulations for tertiary oil recovery. 

Optimizing the formulation of micellar surfactant solutions used for enhanced oil recovery consists of obtaining interfacial tensions as low as possible in multiphase systems, which can be achieved by mixing the injected solution with formation fluids. The solubilization of hydrocarbons by the micellar phases of such systems is linked directly to the interfacial efficiency of surfactants. Numerous research projects have shown that the amount of hydrocarbons solubilized by the surfactant is generally as great as the interfacial tension between the micellar phase and the hydrocarbons. The solubilization of crude oils depends strongly on their chemical composition [155]. 

Both nonionic and anionic surfactants have been evaluated in this application (488,489) including internal olefin sulfonates (487, 490), linear alkylxylene sulfonates (490), petroleum sulfonates (491), alcohol ethoxysulfates (487,489,492). Ethoxylated alcohols have been added to some anionic surfactant formulations to improve interfacial properties (486). The use of water thickening polymers, either xanthan or polyacrylamide to reduce injected fluid mobility mobility has been proposed for both alkaline flooding (493) and surfactant enhanced alkaline flooding (492). Crosslinked polymers have been used to increase volumetric sweep efficiency of surfactant - polymer - alkaline agent formulations (493). 

Lipid. Lipids or surfactants had been used widely in the delivery of pharmacologically active materials in the form of liposomes, emulsions, or micelles. Since the first description of their potential for exogenous gene transfer, much progress has been made in the development of improved cationic lipid structures and formulations with enhanced gene transfection activity. 

In this study, the effects of cosolvent (EtOH) addition on the solubilization and recovery of PCE by a nonionic surfactant (Tween 80) was evaluated using a combination of batch, column and 2-D box studies. Batch results demonstrated that the addition of 5% and 10% EtOH increased the solubilization capacity of Tween 80 from 0.69 g PCE/g surfactant to 1.09 g PCE/g surfactant. For a 4% Tween 80 solution, this translates into a solubility enhancement of more than 50%, from 26,900 mg/L to 42,300. mg/L. When the surfactant formulations were flushed through soil columns containing residual PCE, effluent concentration data clearly showed that PCE solubilization was rate-limited, regardless of the EtOH concentration. Using analytical solutions to the 1-D ADR equation, effective mass transfer coefficients (Ke) were obtained from the effluent concentration data for both steady-state (A e ) and no flow conditions The addition of EtOH had... 

In order to vary interfacial tension over more than four orders of magnitude, several fluid systems were chosen that ranged from high tension surfactant-free formulations to middle phase microemulsions that were at optimal conditions for enhanced oil recovery and had ultralow tensions with the excess brine and oil. Table I lists the specific components used along with their corresponding physical properties. In each case a red water-soluble food coloring dye was added before equilibration to enhance the contrast between phases during microscopy. 

Surfactants are widely used for a variety of reasons, including surface wetting agents, detergents, emulsifiers, lubricants, gasoline additives, and enhanced oil-recovery agents. The type of surfactants selected for a particular application often depends on the chemical and physical properties required and on economics or other considerations such as environmental concerns. To meet these requirements, a typical surfactant formulation may contain blends of a variety of commercial products, which could include ionic and nonionic ethoxylated surfactants, alkylsulfonates, and alkylaryl-sulfonates, and petroleum sulfonates. 

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