Surfactants partitioning

The surfactant partition coefficient in natural sediments determined in laboratory experiments ranges from 1.9 to 2100 L kg-1 for non-ionic, 780 to 2900 L kg-1 for anionic (LAS) and 3800 to 2.5 X 105Lkg 1 for cationic surfactants (see Table 5.4.4). The partition coefficients of cationic surfactants are one or two orders of magnitude higher than for... 

Figure 4 shows phenanthrene and naphthalene sorption isotherms to kaolinite covered with varying levels of sorbed surfactant these levels of surfactant coverage correspond to the different regions existing in the surfactant sorption isotherms discussed earlier (Fig. 1). The linearity of each isotherm was evaluated using Freundlich and linear sorption models. It is apparent from Fig. 4 and Table 4 that HOC partitioning to kaolinite with and without adsorbed surfactants results in linear or near-linear isotherms. As the amount of surfactant adsorbed on the kaolinite surface increased, the sorption of phenanthrene and naphthalene to the solid phase also increased. However, upon normalizing by the amount of sorbed surfactant present, the sorbed surfactant partition coefficient (Kss) decreased with increasing sorbed surfactant amounts (Table 4).

Figure 5. HOC distribution (KD) and sorbed surfactant partition (tf ) coefficients. Kaolinite concentration was 100 g/L, Individual Kss values filled circles) were determined from the KD values using eq 2 and the micellar partition and kaolinite sorption (/fWJT) constants below. Isotherm Ku values open circles) are from Table 4 (linear values), (a) = 1635 M 1. KmitT = 0.002 L/g. (b) = 280 M 1. = 0.0003 L/g. (c) Kmic = 51507 M 1. Kmin -...

Partitioning in the Presence of Surfactant. Partitioning experiments in the presence of Tween 80 were carried out in a manner identical to that discussed above except that 0.1% (w/v) of the surfactant was thoroughly mixed with the water phase before partitioning. Octanol/water partitioning studies carried out with only 0.1% Tween 80 (and no TFMS compound) present initially indicated that at equilibrium, the surfactant partitions approximately 60/40 in favor of the octanol phase. 

Increasing the aqueous phase salinity appeared to increase foam sensitivity to the presence of a hydrocarbon phase. This behavior may be due to increased surfactant partitioning into the oil phase. This can be quantified by determining the ratio of foam volume in the presence of decane to that in the absence of an added hydrocarbon (Table II. Figure 3). With few exceptions, this ratio decreased with increasing aqueous phase salinity. The values of this ratio for AEGS surfactants declined less with increasing aqueous phase salinity than for other surfactants. 

A particularly interesting part of the pilot involved the treating of produced emulsions. Over the life of the pilot, 93% of the injected surfactant was produced at the production wells, and this situation led to serious emulsion problems. Heating the emulsion to a specific, but unreported, temperature caused the surfactant to partition completely into the aqueous phase and leave the crude oil with very low levels of surfactant and brine. The resulting oil was suitable for pipeline transportation. The critical separation temperature had to be controlled to within 1 0. At higher temperatures, surfactant partitioned into the oil, and at lower temperatures, significant quantities of oil remained solubilized in the brine. Recovered surfactant was equivalent to the injected surfactant in terms of phase behavior, and had the potential for reuse. 

Figure 9 shows that tryptophan can be solubilized with the addition of AOT, octanol, and water. At lower pressures, the surfactant partitions mostly into the liquid phase, and tryptophan is only sparingly soluble. At pressures above 140 bar, the liquid phase disappears as the AOT, octanol, and water form micelles in the fluid phase. The micelles cause the solubility of tryptophan to increase dramatically. The solubility becomes well above 0.1 wt.%, which is quite sufficient for practical applications. At pressures above 200 bar in the solid-fluid region, solubilities vary little with pressure, which is consistent with the relatively constant polarities shown in Figure 7 for similar values of Wq. This ability to adjust solubilities of ionic species at modest temperatures and pressures opens up the possibility of interesting new practical applications. 

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. 

Larson (1979) showed that if the phase-volume effects of semimiscible flooding are to be relied on to recover oil (no chemical reduction in So,) without requiring large quantities of chemical, then high-Kc (surfactant partition coefficient), type II(-i-) phase behavior is to be preferred over type II(-) phase... 

Hirasaki (1981) explained why the negative salinity gradient works from the point of phase velocity. He stated that an overoptimum salinity ahead of the surfactant bank is desirable because surfactant that mixes with the high-sahnity water will partition into the oleic phase, and because the phase velocity (fa/S) of the oleic phase is less than unity, the surfactant will be retarded. An underoptimum salinity is not desirable ahead of the surfactant bank because the surfactant partitions into the aqueous phase, which has a phase velocity greater than unity. However, an underoptimum salinity is desirable in the drive to propagate the surfactant. Thus, a system with overoptimum salinity ahead of the surfactant bank and underoptimum salinity in the drive will tend to accumulate the surfactant in the three-phase region where the lowest interfacial tensions generally occur. 

The molecular weight of the surfactant YPS-3A used in this test was 430. The IFT with oil was 0.052 mN/m at 7000 mg/L salinity. During this injection period, no response was observed from the producers. The reason is probably that the IFT was so high the oil films on oil-wet rock surfaces could not be displaced. Another reason for the noneffectiveness is that YPS-3A was so lipophilic that most of the injected surfactant partitioned in the oil phase. Because the producer 930 was converted from an injector, low residual oil saturation existed around the well. Thus, no oil was produced during the pilot test period. 

Chan, K.S., Shah, D.O., 1979. The effect of surfactant partitioning on the phase behavior and phase inversion of the middle phase microemulsions. Paper SPE 7869 presented at the SPE International Symposium on Oilfield and Geothermal Chemistry, Houston, 22-24 January. 

The effect of surfactants on the interfacial tension between water and supercritical fluids is a key property for describing emulsions and microemulsions (8), as shown in Figure 2. The v axis may be any formulation variable that influences surfactant partitioning between the phases such as the pressure or temperature. A minimum in y is observed at the phase inversion point, where the system is balanced with respect to the partitioning of the surfactant... 

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 ]. 

Shell (48) used a simple foam model (49) for their Bishop Fee pilot. The foam generation rate was matched by using an effective surfactant partition coefficient that took into account surfactant losses and foam generation inefficiencies. The value of this coefficient was selected so that the numerical surfactant propagation rate was equal to the actual growth rate. Foam was considered to exist in grid blocks where steam was present and the surfactant concentration was at least 0.1 wt%. The foam mobility was assumed to be the gas-phase relative permeability divided by the steam viscosity and the MRF. The MRF increased with increasing surfactant concentration. The predicted incremental oil production [5.5% of the... 

In two-phase systems, however, where surfactant and water can partition between a fluid and a liquid phase, significant pressure effects occur. These effects were studied for AOT in ethane and propane by means of the absorption probe pyridine N-oxide and a fluorescence probe, ANS (8-anilino-l-naphthalenesulfonic acid) [20]. The UV absorbance of pyridine A-oxide is related to the interior polarity of reverse micelles, whereas the fluorescence behavior of ANS is an indicator of the freedom of motion of water molecules within reverse micelle water pools. In contrast to the blue-shift behavior of pyridine N-oxide, the emission maximum of ANS increases ( red shift ) as polarity and water motion around the molecule increase. At low pressures the interior polarity, degree of water motion, and absorbance intensity are all low for AOT reverse micelles in the fluid phase because only small amounts of surfactant and water are in solution. As pressure increases, polarity, intensity, and water motion all increase rapidly as large amounts of surfactant and water partition to the fluid phase. The data indicate that the surfactant partitions ahead of the water thus there is a constant increase in size and fluidity of the reverse micelle water pools up to the one-phase point. An example of such behavior is shown in Fig. 4 for AOT in propane with a total fVo of 40. The change in the ANS emission maximum suggests a continuous increase in water mobility, which is due to increasing fVo in the propane phase, up to the one-phase point at 200 bar. 

Figure 6 Effect of salinity on interfacial tension and surfactant partitioning in 0.2% TRS 10-80-brine-octane system.

The phase-inversion temperature (PIT) is the temperature at which the continuous and dispersed phases of an emulsion system are inverted (e.g. an o/w emulsion becomes a w/o emulsion, and vice versa). This phenomenon, introduced by Shinoda (16), occurs for emulsion systems containing non ionic surfactants, and can be a valuable tool for predicting the emulsion behaviour of such systems. The phase inversion occurs when the temperature is raised to a point where the interaction between water and the nonionic surfactant molecules decreases and the surfactant partitioning in water decreases. Hence, surfactant molecules... 

In general, their work indicates that the surfactant partition coefficient between the oil phase and the excess brine phase is unity at the optimal parameter value. Their work indicates that there is a strong similarity between the interfacial tension behavior of low concentration systems and those of high concentration systems. Bansal and Shah (104) also showed that the salt tolerance of surfactant systems can be extended to rather high salt concentrations by mixing ethoxylated sulfonates with the usual petroleum sulfonate materials. An optimal salinity as high as 32% sodium chloride was observed in one of the mixed systems which was also characterized by very low oil-water interfacial tensions. 

The influence of alcohols on phase behavior is known as mainly effective inside phases (1-3), for instance, by changing the optimal salinity for a given oil-surfactant system (4-6) or the surfactant partitioning between the oil and brine (7-9). Therefore, it becomes convenient to look at the problem in two separate steps ... 

The effect of alcohol on surfactant mass transfer from bulk solution to the oil/dilute micellar solution interface was studied Various interfacial properties of the surfactant solutions and their ability for displacing oil were determined. For the surfactant-oil-brine systems studied, the interfacial tension (IFT) and surfactant partition coefficient did not change when isobutanol was added to the following systems 0.1% TRS 10-410 in 1.5% NaCl vs. n-dodecane and 0.05% TRS 10-80 in 1.0% NaCl vs. n-octane. On the other hand, the interfacial viscosity, oil drop flattening time (i.e. the time required for an oil droplet to flatten out after being deposited on the underside of a polished quartz plate submerged in the micellar solution) and oil displacement efficiency were influenced markedly by the addition of alcohol. 

In general, the surfactant formulations used for enhanced oil recovery contain a short chain alcohol. The addition of alcohol can influence the viscosity, IFT and birefringent structures of micellar solutions as well as coalescence rate of oil ganglia. The present paper reports the effect of addition of isobutanol to a dilute petroleum sulfonate (< 0.1% cone) solution on IFT, surface shear viscosity, surfactant partitioning, the rate of change of IFT (or flattening time) of oil drops in surfactant solutions and oil displacement efficiency. The two surfactant systems chosen for this study indeed exhibited ultralow IFT under appropriate conditions of salinity, surfactant concentration and oil chain length (11,15,19). 

The study revealed that the addition of isobutanol to dilute TRS 10-80 or TRS 10-410 petroleum sulfonate solutions did not influence significantly IFT, or surfactant partitioning but decreased interfacial viscosity and markedly reduced flattening time of oil drops and increased oil displacement efficiency, presumably by promoting coalescence of oil ganglia in porous media. 

The effect of salinity on oil displacement efficiency revealed that for the alcohol containing formulations, the nonequilibrated system was more efficient for oil recovery as compared to the equilibrated system at and above optimal salinity. It is proposed that not only the equilibrium values of the parameters such as interfacial tension and interfacial viscosity are important but the dynamic process of surfactant partitioning is also important... 

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