Salinity, optimal

The temperature (or salinity) at which = o mt called the optimal temperature (or optimal salinity), because at that temperature (or salinity) the... 

Including a surfactant in the caustic formulation (surfactant-enhanced alkaline flooding) can increase optimal salinity of a saline alkaline formulation. This can reduce iaterfacial tension and increase oil recovery (255,257,258). Encouraging field test results have been reported (259). Both nonionic and anionic surfactants have been evaluated in this appHcation (260,261). 

The IFT trend with increasing disulfonate content is not surprising. Increasing the di.monosulfonate ratio increases both water solubility and optimal salinity of the AOS surfactant. The test solvent was aqueous 3% NaCl. As the di.monosulfonate ratio increases, the surfactant solution becomes increasingly underoptimal. 

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 thrust of surfactant flooding work has been to develop surfactants which provide low interfacial tensions in saline media, require less cosurfactant, are effective at low concentrations, and exhibit less adsorption. The optimal salinity concept and the... 

Both commercial grade and pure nonionic and anionic surfactants have been evaluated by phase inversion and optimal salinity screening procedures to establish relationships to their molecular structures. 

Optimal Salinities Because the EACN values ascribed to oil systems are usually derived from salinity scanning, it was considered appropriate to evaluate the salinity tolerance of ICI NP6, and to determine the EACN value for toluene so that a comparison could be made between the two experimental techniques employed in this study. Inspection of Table III reveals an EACN value for toluene of -10.3 which can be compared to the value of -16 determined from PIT data. Such large negative values... 

Optimal Salinities Phase inversions at optimal salinity were assessed routinely by salt titrations into systems maintained at constant temperature. For the Leonox IOS surfactant system, increasing levels of salinity were necessary to cause the emulsion state to phase invert as the alkane molecular weight increased (Figure 11). Ihe initial conductivity value at the condition where zero salt had been added may in part reflect the salt contamination naturally present within the supplied formulation. Ihe internal olefin sulphonate species again revealed a linear relationship between EACN and optimal salinity as did all ionic formulations under test (see Figures 12 and 13, plus Table III). Ihe estimation of EACN values for both toluene... 

TABLE III SUMMARY OF OPTIMAL SALINITY DATA AND APPROPRIATE DERIVED EQUIVALENTS... 

Figure 14. Optimal salinity variation for decane/cyclohexane blends...

In the absence of alcohol the salinity/alkane sensitivity will be dominated by the nature of the surfactant hydrophile. A linear response was observed between optimal salinity and alkane chain length for the ICI NP6 surfactant with a recorded coefficient of ds /d EACN = 17.Sgdm "3/1 EACN. This high salt tolerance was expected for nonionics and can reflect an... 

Optimal Salinities The phase inversion process may be considered to reflect the balanced nature of the adsorbed surfactant species at the oil/water interface. Simple geometric packing... 

If favourable crude oil inversion conditions are observed it is possible to calculate alkane equivalences based on either optimal salinity or PIT data. 

Commercial sulphonate formulations behave in a manner qualitatively similar to that expected from pure components during optimal salinity evaluation. 

Optimal salinity values directly influence the nature of the ionic groups, while temperature variations (PIT tests) strongly effect the oxyethylene linkages. 

The temperature (or salinity) at which optimal temperature (or optimal salinity), because at that temperature (or salinity) the oil—water interfacial tension is a minimum, which is optimum for oil recovery. For historical reasons, the optimal temperature is also known as the HLB (hydrophilic—lipophilic balance) temperature (42,43) or phase inversion temperature (PIT) (44). For most systems, all three tensions are very low for Tlc < T < Tuc, and the tensions of the middle-phase microemulsion with the other two phases can be in the range 10 5—10 7 N/m. These values are about three orders of magnitude smaller than the interfacial tensions produced by nonmicroemulsion surfactant solutions near the critical micelle concentration. Indeed, it is this huge reduction of interfacial tension which makes micellar-polymer EOR and its SEAR counterpart physically possible. 

Thus, given the optimal salinity for an unknown oil, it is possible to back-calculate the oil EACN. However, this is not helpful in designing the surfactant system in the first place. It is desirable to characterize the oil EACN using an alternate approach. One such approach uses alcohol partitioning as an indicator of an unknown oil EACN. The partition coefficient(ky) for low concentrations of alcohol between water and NAPL is dependent upon the NAPL EACN where kjj is defined as the concentration of the alcohol in the NAPL (mg/L) divided by the concentration of the alcohol in the water. The subscripts i and j refer to the NAPL and... 

In using microemulsions to enhance oil recovery from petroleum reservoirs (see Section 11.2.2) the concept of optimal salinity has evolved. By optimal salinity is meant the salinity for which O/W interfacial tension is lowest and oil recovery is... 

Figure 3.29 Illustrations of changes occurring in physical properties and other phenomena in the region of the optimal salinity for enhanced oil recovery using surfactant flooding. From Sharma [235]. Copyright 1991, Plenum Press.

Each of the components inhabits this or that zone of the sea depending on its dwelling and reproduction range and features the highest density under the conditions of its optimal salinity. 

Macroscopic Dlspersivity. a is of interest in many enhanced oil recovery displacements (sucn as development of miscibility or generation of optimal salinities) where local mixing controls the success of the displacement. V/e can also extract u from the randomly heterogeneous runs discussed above but our concTusions are much less precise because we have no theoretical model like Equation 1 for local mixing in two-dimensional flow. But we can compare to u under identical circumstances. 

The influence of sodium acetate on the phase equilibria of acrylamide microemulsions has been investigated (Holtzscherer, C. Candau, F. J. Colloid Interface Sci., in press). The interfacial tensions of the systems preequilibrated are reported versus the salt concentration in Figure 6. It can be seen that addition of sodium acetate induces a phase transition HI - H III which occurs for S = 1.2H. The intercept of the two curves which occurs in the Vinsor III domain defines an optimal salinity for the formation of bicontinuous microemulsions. 

Surfactant Mixing Rules. The petroleum soaps produced in alkaline flooding have an extremely low optimal salinity. For instance, most acidic crude oils will have optimal phase behavior at a sodium hydroxide concentration of approximately 0.05 wt% in distilled water. At that concentration (about pH 12) essentially all of the acidic components in the oil have reacted, and type HI phase behavior occurs. An increase in sodium hydroxide concentration increases the ionic strength and is equivalent to an increase in salinity because more petroleum soap is not produced. As salinity increases, the petroleum soaps become much less soluble in the aqueous phase than in the oil phase, and a shift to over-optimum or type H(+) behavior occurs. The water in most oil reservoirs contains significant quantities of dissolved solids, resulting in increased IFT. Interfacial tension is also increased because high concentrations of alkali are required to counter the effect of losses due to alkali-rock interactions. 

Interfacial tensions versus density differences between phases o, middle phase microemulsion, top phase o, middle phase microemulsion, bottom phase. The horizontal arrows indicate the common value y of the two interfacial tensions at the optimal salinity the vertical arrows indicate the density difference relative to the transition between three phase and two phase domains. The line represents the expected scaling law their slope is 4. 

The physicochemical aspects of micro- and macroemulsions have been discussed in relation to enhanced oil recovery processes. The interfacial parameters (e.g. interfacial tension, interfacial viscosity, interfacial charge, contact angle, etc.) responsible for enhanced oil recovery by chemical flooding are described. In oil/brine/surfactant/alcohol systems, a middle phase microemulsion in equilibrium with excess oil and brine forms in a narrow salinity range. The salinity at which equal volumes of brine and oil are solubilized in the middel phase microemulsion is termed as the optimal salinity. The optimal salinity of the system can be shifted to a desired value hy varying the concentration and structure of alcohol. 

---