Optimal Surfactant Formulation

The Optimal Surfactant Formulation model can be considered as an extension of the PIT concept for complex surfactant mixtures. In 1973, the oil embargo caused a considerable amount of research aimed at enhanced oil recovery. Among the proposed methods were low-tension surfactant flooding processes, in which a surfactant solution was injected into the oil reservoir to produce a low interfacial tension between the crude oil and water, in order to reduce the capillary pressure resistance. The researchers were aiming at an optimal surfactant formulation , at which the interfacial tension has a minimum, i.e. at the balanced surfactant composition. The systems studied represented very complex mixtures, containing polydisperse surfactants, alcohols, salts, hydrocarbons, and water. Elaborate em- 

Here S is the NaCl concentration in wt%, ACN, or Alkane Carbon Number, is a characteristic parameter of the oil phase, A7 is the temperature deviation from a certain reference (25 C), f(A) is a function of the alcohol type and concentration, and K, o, and Ut are empirical parameters characterizing the surfactant. A similar empirical equation was proposed for nonionic surfactants -  

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Oil contaminants can range in both viscosity and molecular weight. The purpose of this work was to find optimal surfactant formulations to extract low viscosity ( ( 100 cp), high molecular weight (hydrophobic) oils. In surfactant formulation it is common to define the oil molecular weight (hydrophobicity) by virtue of its equivalent alkane carbon number (EACN) aka, how many carbons would there be in an alkane oil of equivalent behavior. Thus, since some crude oils behave similarly to hexane, and since hexane has an alkane carbon number of 6, these crude oils also have an... 

Bettahar, M., Schafer, G., and Baviere, M. (1999), An Optimized Surfactant Formulation for the Remediation of Diesel Oil Polluted Sandy Aquifers, Environmental Science and Technology, 33, 1269-1273... 

The Kabalnov-Weimerstrom theory provides a qualitative explanation for the oriented wedge trend in macroemulsion stability, i.e. it explains the PIT and Optimal Surfactant Formulation behavior of macroemulsions, as well as the multilamellar stabilization. For a quantitative comparison, the data for only one system is currently available.A detailed comparison will be made below. 

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]. 

It was observed that the formulations consisting of ethoxylated sulfonates and petroleum sulfonates are relatively insensitive to divalent cations. The results show that a minimum in coalescence rate, interfacial tension, surfactant loss, apparent viscosity and a maximum in oil recovery are observed at the optimal salinity of the system. The flattening rate of an oil drop in a surfactant formulation increases strikingly in the presence of alcohol. It appears that the addition of alcohol promotes the mass transfer of surfactant from the aqueous phase to the interface. The addition of alcohol also promotes the coalescence of oil drops, presumably due to a decrease in the interfacial viscosity. Some novel concepts such as surfactant-polymer incompatibility, injection of an oil bank and demulsification to promote oil recovery have been discussed for surfactant flooding processes. 

Salinity Tolerance. As the petroleum reservoir salinity can be very high, the surfactant formulations should be designed for high salt tolerance. The widely used petroleum sulfonates for enhanced oil recovery exhibit relatively low salt tolerance in the range 2-2.5% NaCl concentration, and even smaller for the optimal salinity. The presence of divalent cations in the brine decreases the optimal salinity of surfactant formulations (44). 

Since optimal salinity leads to a favorable condition for maximum oil recovery, one would like to design methods to adjust the optimal salinity of a given surfactant formulation (45.46). Figure 10 shows the optimal salinity of a mixed surfactant formulation consisting of a petroleum sulfonate and an ethoxylated sulfonate. It is evident that the optimal salinity of the formulation increases with increasing concentration of ethoxylated sulfonate, the optimal salinity increases from 1% to 24% NaCl brine. Moreover, it is interesting to note that these formulations, when equilibrated with... 

The flow through porous media behavior of various macroemulsions was studied by measuring the pressure drop across a porous medium (Figure 13). It is obvious that a minimum in pressure drop occurs near the optimal salinity of the surfactant formulation. One can conclude that the interfacial tension is an important parameter which influences the pressure drop across porous media (53). 

Salinity Salinity plays at least two important roles, namely it maintains the integrity of the reservoir and it balances the physicochemical environment so that surfactant formulation stays close to optimal. Thus, ultra-low interfacial tension and oil solubilisation are very sensitive to salinity. Mixing of the surfactant slug with connate water may alter the surfactant formulation mainly due to dilution and to the incorporation of new electrolytes to the formula. Adsorption and desorption of electrolytes, particularly divalent cations, onto or from solid materials such as clay, will also change the salinity of the aqueous phases to some extent and may cause surfactant precipitation, which is however not always an adverse effect [151]. In order to attenuate the undesirable salinity effects on formulation, surfactants able to tolerate salinity changes [109], high salinity [150] and the presence of divalent ions [112] maybe used. 

Alcohol composition Just as electrolytes do, alcohols help to balance the physicochemical environment in order to keep the surfactant formulation close to optimal, according to the so -called/(A) or ( A) effects discussed in Chapter 3. Besides, even so some surfactant formulations do not contain alcohols, they are often added into microemulsion systems as co-solvents (particularly in those containing anionic surfactants) to improve the solubility of the main surfactants and prevent the formation of highly viscous meso-phases [114] such as liquid crystals, which are additionally known to stabilise the emulsions that may be formed. Alcohols can also change the surfactant partition coefficients which has a great effect on the oil recovery efficacy [ 110,111 ]. 

Table 1. Optimal salinity of surfactant formulation containing TRS 10-410, EOR-200 and Isobutyl Alcohol. 

Bansal, V.K. and Shah, D.O., The Effect of Ethoxylated Sulfonates on Salt Tolerance and Optimal Salinity of Surfactant Formulations for Tertiary Oil Recovery.,... 

The salinity of poljmier solution can influence four major parameters of surfactant-pol)mi r flooding process, namely, interfacial tension, mobility control, surfactant loss and phase behavior. When polymer solution of various salinities are equilibrated with surfactant solution in oil, the formation of lower, middle and upper phase microemulsion has been observed (1) similar to the effect of increasing connate water salinity (2,3). In general, there is an optimal salinity (2) which produces minimum interfacial tension and maximal oil recovery (1,4). On the basis of interfacial tension alone, the salinity of polymer solution should then be designed at or near the optimal salinity of the preceding surfactant formulation. 

The mechanism of the above results which has been described in detail elsewhere (1) is summarized as follows. When the salinity of pol3nner solution is at the optimal salinity of the preceding surfactant formulation, middle phase microemulsion is produced in situ, which has ultra-low interfacial tension with resident brine, residual oil and polymer solution. This ultra-low interfacial tension together with adequate mobility control will allow the displacement of the surfactant slug in a piston-like manner. Consequently, favorable oil recovery can be obtained over a wide range... 

It should be mentioned that the necessary conditions for the validity of the above stated conclusions are that (1) the optimal salinity of the surfactant formulation remains approximately constant upon dilution, (2) there is a sharp minimum of IFT occurring at the optimal salinity, (3) mobility control is adequately... 

Tertiary oil recovery in Berea cores by soluble oils was studied. Hexadecane instead of dodecane was used in this study. Two connate water salinities were used. One was 2.1% NaCl (the optimal salinity of the surfactant formulation) and the other was 3% NaCl + 1% CaCl2 The results are shown in Table 2. For both connate water salinities, maximal oil recovery was obtained when the salinity of polymer solution was 2.1% NaCl. Surfactant... 

When the salinity of pol)nner solution was at the optimal salinity of the preceding surfactant formulation, oil recovery in sand packs was favorable over a wide range of connate water salinities for both aqueous and oleic surfactant formulations. Oil recovery drastically decreased when the salinity of polymer solution was shifted from the optimal salinity even when the connate water was at the optimal salinity. These results indicate that the processes occurring at the surfactant slug-polymer solution mixing zone dominate the oil recovery efficiency. 

For oil displacement in Berea cores especially in the presence of 1% CaCl2 in connate water, surfactant loss was quite significant and the oil recovery was greatly reduced. Maximal oil recovery was obtained when the salinity of polymer solution was at or slightly below the optimal salinity of surfactant formulation,... 

HSAS, with its surface activity and solubility, is weight effective and can be used by the formulator to deliver superior cleaning performance versus traditional surfactants. HSAS can also be used to optimize surfactant level in laundry detergent products. P G partnered with Shell to develop HSAS. 

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