Solubilization parameter

Figure 13 shows the relation between the solubilization parameter and optimal salinity for three AOS surfactants under realistic conditions (50°C, brine for-... 

IFTs and solubilization parameters do not change abruptly around the optimal salinity as shown in Fig. 14. IFTs are less than 0.01 dyne/cm within a fairly wide range of salinities. 

The conclusion from the work by Baviere et al. [41] is that the main advantage of AOS is that it has optimum phase behavior (i.e., high solubilization parameters and low IFTs) from low to high temperatures across a range of salinities. 

It is widely recognized that the system IFT reaches a minimum in the middle phase microemulsion region. At the same time, the solubilization parameter (a), defined as mass of oil solubilized per unit mass of surfactant, is maximized in middle phase microemulsion systems (see Figure 1). This inverse relationship between the solubilization parameter (c)and IFT (y)has been defined by the Chun-Huh equation (Huh 1979, Sunwoo et. al. 1992, Abe et. al. 1987) ... 

Figure (3) shows the solubilization parameters as functions of water concentration for SDS/2- entanol ratios of 0.25 and 0.40 at 25 C. The solubilization parameters are defined as Vo/Vs and Vw/Vs, where Vo, Vs and Vw are the volumes of organic phase, surfactant and aqueous phase in the microemulsions. The parameters are related to the drop size and also interfacial torsions f7.23). The bicontinuous phase is located around the composition range corresponding to equal values of solubilization parameters. The solubilization parameters are dependent on the initial surfactant and/or cosurfactant concentration. Similar dependence has been observed in other systems as a function of salinity and pH (7.231. Conductivity measurements performed as a function of water content indicate an S-shaped curve as shown in Figure (4). This is typical of microemulsions showing transition from oil-continuous to bicontinuous to water-continuous microstructure with increasing water content. 

Micellar-polymer flooding and alkali-surfactant-polymer (ASP) flooding are discussed in terms of emulsion behavior and interfacial properties. Oil entrapment mechanisms are reviewed, followed by the role of capillary number in oil mobilization. Principles of micellar-polymer flooding such as phase behavior, solubilization parameter, salinity requirement diagrams, and process design are used to introduce the ASP process. The improvements in ""classicaV alkaline flooding that have resulted in the ASP process are discussed. The ASP process is then further examined by discussion of surfactant mixing rules, phase behavior, and dynamic interfacial tension. 

Salinity Requirement Diagrams. Maximum solubilization parameter occurs very close to the salinity at which maximum core-flood oil... 

Healy et al. (1976) found that a large number of anionic surfactant systems exhibited good correlations between interfacial tension and solubilization parameter. Healy and Reed (1977a, 1977b) proposed the following correlation by fitting experimental data, as schematically shown in Figure 7.27 ... 

Huh developed a theoretical relationship between the solubilization parameter and IFT for a middle-phase microemulsion (type III). His equations are... 

We start with the equations by Huh (1979) who developed a theoretical relationship between the solubilization parameter and IFT for a middle-phase microemulsion (type 111). His equations are shown as Eqs. 7.77 and 7.78. According to Eq. 7.96,... 

Puerto, M.C., Gale, W.W., 1977. Estimation of optimal salinity and solubilization parameters for alkylorthoxylene sulfonate mixtures. SPEJ 17 (3), 193-200. 

FIGURE 9.3 Interfacial tensions and solubilization parameters for microemulsions in a system containing a synthetic petroleum sulfonate, an alcohol cosurfactant, a mixture of refined oils, and NaCl brine. (From Reed, R.L. and Healy, R.N., in Improved Oil Recovery by Surfactant and Polymer Flooding, Shah, D.O. and Schechter, R.S., Eds., Academic Press, New York, 1977. With permission.)... 

The volume of the oil phase (in mL) solubilized per gram of surfactant used at the conditions where equations 8.10 or 8.11 are equal to zero ( optimum salinity ) is called the solubilization parameter at optimum formulation and symbolized by SP. The interfacial tension under these conditions, y, is inversely proportional to the SP, and y = K/(SP )2 (Chun, 1979). Consequently, to obtain the lowest interfacial tension (Chapter 5, Section IIIA), the value of SP should be maximized. 

Fig. 13 Effect of electrolyte concentration on Winsor microemulsion type (saliniu scan), w water o oil m microemulsion solubilization parameter volume of oil solubilized per mass of surfactant.

There are two bulk interfaces in middle phase microemulsions and one in lower or upper phase microemulsions. Thus, one or three values of interfacial tension (IFT) may be measured depending on system composition (1) ymo between microemulsion and excess oil phase, (2) between microemulsion and excess brine phase, and (3) >Vm between excess oil and brine phases. Phase volumes and consequently the volumes of oil (Vo) and brine () solubilized in the microemulsion depend on the variables that control the phase behavior. The solubilization parameters are defined as Vg/Vs and V JV, where Vs is the volume of the surfactant in the microemulsion phase. These parameters are easily determined from phase volume measurements if all the surfactant is assumed to be in the microemulsion phase. The magnitude of decreases as Vg/Vs increases, i.e., as more oil is solubilized. Similarly, the magnitude of decreases as Vg/Vs increases. The salinity at which the values of ymo and are equal is known as the optimal salinity based on IFT. Similarly, the intersection of Vg/Vs and V. /Vs defines the optimal salinity based on phase behavior. The optimal salinity concept is very important for enhanced oil recovery. 

FIGURE 4.25 Interfadal tensions and solubilization parameters for a system containing 2% of a petroleum sulfonate surfactant and 1% of a short-chain alcohol. is the interfacial... 

The first step in selecting an optimal micellar system for any field application is to define a complete one-phase microemulsion without any oil or water phase separation, whose viscosity is in the range of the equivalent viscosity of the oil-bank, and which can be prepared from a minimum amount of surfactant, corresponding to the smallest multiphase area in phase diagrams or to the highest solubilization parameters. Such a system involves a surfactant... 

The alcohol concentration in the middle phase is higher than the value calculated according to the solubilization parameters and the alcohol concentration in the excess phases. This implies that the alcohol is involved in the interfacial structures of the middle phase, and is further verified by studies involving changing the surfactant/alcohol ratio. 

In addition, it will be shown that a composition change in a given system may greatly change the phase compositions, namely that of the middle phase. So, to obtain information on interfacial and structural effects, it is necessary to compare different compositions under such conditions that the type of the system is always the same. Here we chose the S3nranetrical type III as the reference state which means that the middle phase exhibits a water-to-oil ratio (WORj ) equal to one. This kind of system, at least when sulfonates are used, corresponds from an interfacial and phase behavior point of view to the optimum conditions for the oil recovery process, i.e. lowest interfacial tension and high solubilization parameters for water and oil. 

Table 2 shows that there is a strong decrease in the alcohol concentration in all three phases and, at the same time, an increase in the middle phase volume—from 7 to 21 volume %—when the WOR is increased from 0.27 to 5.23. This result strikingly demonstrates an important effect of the alcohol. Decreasing the alcohol content increases the solubilization parameters and the multiphase zone becomes smaller. This trend has been reported by Salter (7). 

The formation of a compact state stabilized by hydrophobic interactions in the copolymers containing side chains of four or more methylene groups suggests the presence of intramolecular micelles. Solubilization measurements [9] were made with a lipophilic water insoluble dye, yellow OB, by the method of Ito et al. [4]. In Figure 4, the solubilization parameter, S, expressed as moles of dye solubilized per... 

Fig. 4. The dependence of the solubilization parameter on the degree of dissociation in pure water at 22 °C for ethyl- (O), butyl- (B-1 3, B-II , B-III C) and hexyl- (A) copolymers. Polymer concentrations 0.05 eq. except for hexyl-, 0.01 eq.

Figure 10. Solubilization parameters vs. temperature for a crude oil system. (Reproduced with permission from reference 50, copyright 1996 Elsevier.)...

In the previous relationship, the solubilization parameters SP refer to the Vo/Vs and Vw/l s ratios of the volume of oil and water solubilized in the microemulsion phase (the surfactant-rich phase) per volume of surfactant. If the surfactant is a solid, and as a more general definition, the solubilization parameters may be taken as Vo/nts and V ulfn, where ms is the mass of surfactant. The volumes can be deduced firom the measurement of the microemulsion-phase volume at equilibrium mid the amount of surfactant, oil, and water that were added to the system in the first place. It is helpful to note that in two- or three-phase systems, the excess phase(s) contain(s) at most the critical micelle concentration of the surfactant, which is, in general, a negligible amount in the mass balance. Thus, all the surfactants can be assumed to be in the microemulsion phase, and the excess phase can be assumed to be a pure component. 

A typical variation of the interfacial tension and solubility parameters is shown in Fig. 20 [63] 7mo and 7mw refer to the interfacial tensions between the microemulsion (water phase) and the excess oil, and between the microemulsion (oil phase) and the excess water, respectively. The solubilization parameters are also defined for two- and three-phase systems. In the last case, the two solubilization parameters can be measured at the same time, Vo and Vw being the amount of oil and the amount of water, respectively, that are solubilized into the middle-phase microemulsion. 

As seen in Fig. 20, the solubilization parameter curves cross over at exactly the same formulation (here salinity) where the interfacial tension curves do it, which is expected if the Hu relationship strictly applies. At this point, which is by definition the optimum formulation of the scan, the microemulsion is solubilizing the same amoimt of oil and water (as V = Vw) and its representative point on a SOW diagram is exactly at the same distance from the W and O vertices. As seen in Fig. 20, the solubilization increases from both sides when the formulation tends to the optimum one. The value of the solubilization parameter at optimum is generally referred to as SP (the maximum of the minimum of the Vq/Vs and Vw/Vs ratios that is attained at Vq/Vs = It is worth noting that SP ... 

Figure 20 Interfacial tensions and solubilization parameters for an anionic system containing alkyl ortho xylene sulfonate, tert-amyl alcohol, and an oil mixture. (From Ref. 63.)...

Table 5.8 Micellar solubilization parameters for steroids in n-alkylpolyoxyethylene surfactants at 25° C. From Barry and El Eini [145].

Table 6.18 Solubilization parameters for the steroids in polyoxyethylene (23) dodecyl ether (C12E23) and partition coefl cients between water and n-octanol, Pocunoi water and ether, at 25 TC (from [158])... 

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