Emulsification salinity

Study of Emulsification. The emulsions used for this experimental study were the oil-in-water type. Water external emulsions are easily injected, stable at the low salinities encountered in steamflooded reservoirs, and expected to produce more stable blockage at elevated temperatures (17). 

Although not included in this paper, a field experiment has been designed for the Kern River Unit located at the edge of the Kern River field, Kern County, California. The ideal emulsification properties of the crude oil have already been discussed in this paper. This field is an example of reservoir properties that should be considered ideal when selecting a reservoir for future testing of the process heterogeneous production zones, areas of low and high oil saturations, low salinity, low clay content, and crude oil that is easily emulsified. 

As in the previous study (4), the experiments involve brine-alcohol-petroleum sulfonate mixtures brought into contact with oil. In these systems, which are the type used for enhanced oil recovery, the initial mixtures are, depending on the salinity, either stable dispersions of lamellar liquid crystal and brine or a single liquid crystalline phase. The latter is formed at higher salinities than the former, in accordance with the general pattern of phase behavior in such systems described elsewhere ( 5). Indeed, one aspect of our work which differs from studies made by others of spontaneous emulsification in enhanced oil recovery processes (6-7) is emphasis on the need to understand the role of liquid crystals in the overall nonequilibrium process. Related studies of spontaneous emulsification in other systems are reviewed elsewhere... 

After describing the experimental technique in the next section, we report our observations of intermediate phase formation and spontaneous emulsification in three parts corresponding to three types of equilibrium phase behavior found when equal volumes of oil and the surfactant-alcohol-brine mixtures are equilibrated. The three types are well known (8-9) and, in order of increasing salinity, are a "lower" phase, oil-in-water microemulsion in equilibrium with excess oil, a "surfactant" or "middle" phase, probably of varying structure, in equilibrium with both excess oil and excess brine, and an "upper" phase, water-inoil microemulsion in equilibrium with excess brine. 

At approximately optimum salinity, spontaneous emulsification of brine drops in the oil phase began in both systems. This phenomenon resulted from local supersaturation of the oil phase, as explained in the discussion section below. The amount of emulsification tended to increase with increasing salinity. As a result, the cloud of emulsion drops began to obscure the interface between the microemulsion and oil, making interface position measurements difficult. These observations of spontaneous emulsification confirm the results of the earlier contacting experiments performed in the horizontal configuration ( 4). 

The transition from the three-phase to two-phase region in the PDM system was marked by a sudden increase of spontaneous emulsification in the oil phase. Because formation of an intermediate microemulsion ceased at this point, the emulsion drops remained near the brine interface rather than rapidly moving away to form a single-phase region above the brine. An example of this behavior is shown in Figure 15 for the 2.1 gm/dl-salinity PDM system. 

Calculated diffusion paths also successfully predicted the occurrence of spontaneous emulsification in the systems. Near optimum salinity where this phenomenon first appeared, brine drops spontaneously emulsified in the oil but were isolated from the bulk brine phase by a microemulsion. At high salinities, a more common type of spontaneous emulsification was seen with brine emulsifying in the oil directly above a brine layer. 

Figure 22. Expanded view of the oii corner showing the onset of spontaneous emulsification at optimum salinity.

In emulsification and entrainment, the crude oil is emulsified in situ owing to IFT reduction, and it is entrained by the flowing aqueous alkaline solution (Subkow, 1942). The conditions for this mechanism to occur are high pH, low acid number, low salinity, and OAV emulsion size < pore throat diameter. 

FIGURE 9.12 High-salinity diffusion path for contact of composition D with oil (O) indicating an intermediate brine phase (b) and spontaneous emulsification in the oil phase (s.e.). Ic and w/o denote the lamellar liquid crystalline phase and a water in oil microemulsion, respectively. S/A denotes the surfactant/alcohol mixture in this pseudoternary diagram. (From Raney, K.H. and Miller, C.A., AIChE J., 33, 1791, 1987. With permission.)... 

Complete information on phase behavior including tie-lines and on diffusion coefficients is rarely available for oil-water-surfactant systems. Nevertheless, Raney and Miller used plausible phase diagrams for an anionic surfactant-NaCl brine-hydrocarbon system as a function of salinity to calculate diffusion paths that exhibited intermediate phase formation and spontaneous emulsification in agreement with experimental observations made using the vertical cell technique. For example. Figure 9.12 shows a diffusion path for a surfactant-alcohol-brine mixture of composition D in contact with oil for a case when initial salinity is high. An intermediate brine phase is predicted as well as spontaneous emulsification in the oil phase, both of which were, in fact, observed. 

Mixtures containing 1 wt% of the pure nonionic surfactant C,2E5 in water were contacted with pure n-hexadecane and n-tetradecane at various temperatures between 25 and 60°C using the vertical cell technique. Similar experiments were performed with C,2E4 and n-hexadecane between about 15 and 40°C. In both cases the temperature ranged from well below to well above the phase inversion temperature (PIT) of the system, i.e., the temperature where hydrophilic and lipophilic properties of the surfactant are balanced and a middle phase microemulsion forms (analogous to the optimal salinity for ionic surfactants mentioned above). The different intermediate phases that were seen at different temperatures and the occurrence of spontaneous emulsification in some but not all of the experiments could be understood in terms of known aspects of the phase behavior, e.g., published phase diagrams for the C12E 5-water-n-tetradecane system, and diffusion path theory. That is, plausible diffusion paths could be found that showed the observed intermediate phases and/or spontaneous emulsification for each temperature. 

The methods of emulsion breaking (de-emulsification) are of importance in various areas of industry [39,61], especially in oil recovery in crude petroleum the content of highly saline water may be as high as 50 - 60%. Oil-soluble surfactants present in petroleum (asphaltenes, porphyrines, etc) and those introduced during tertiary recovery form highly developed adsorption layers at the water surface, and thus create structural-mechanical... 

FIGURE 6.24 (a) Diffusion path at optimal salinity in a model oil-surfactant-brine system, (b) Enlargement of an oil corner showing local supersaturation leading to spontaneous emulsification. Reprinted with permission from Raney and Miller (1985). Copyright (1985) American Chemical Society. 

The recovery of naturally acidic oils by alkaline flooding fits into the phase alteration category. The recovery mechanisms of these floods are varied since the surface active salts, which are formed by the in situ acid-base reaction, can adsorb onto the oil-water interface to promote emulsification or can absorb onto the rock surface to alter wettability. The exact recovery mechanism, recently reviewed by Johnson (3) depends on the pH and salinity of the aqueous phase, acidity of the organic phase and wettability of the rock surface (4,5). In this study an additional alkaline recovery mechanism is explored. This mechanism. Emulsification and Coalescence, depends on the valency of the electrolyte as well as the pH and salinity of the aqueous phase. The Emulsification and Coalescence mechanism for the recovery of acidic oils is similar to the Spontaneous Emulsification mechanism suggested by Schechter et al. (6) for the recovery of nonacidic oils with petroleum sulfonate solutions. 

Emulsification and entrainment The emulsification and entrainment mechanism was observed to occur during high pH flooding of low-acid number oils in low salinity environments. This mechanism is manifested by partial entrainment and partial entrapment of the emulsion phase. Complete entrainment of the emulsion... 

Run DY-15 shown in Figure 4, In this experiment, the flow rate decreased to zero just before breakthrough of the driving fluid (at about T = 0.6 PV in a nominal waterflood). Substantial differences in the upstream pressure of the flow apparatus (400 psi at T = 1.2 PV) and the differential pressure across the core (75 psi at T = 1.2 PV) indicate that most of the emulsification and entrapment occurred in the entrance region of the sandpack. This mechanism was repeatedly observed in high pH, non-saline floods of moderate acid number (> 2.0) oils. 

Emulsification and wettability alteration Increases in the recovery rate and the microscopic mobilization efficiency of residual oil were observed in high pH/high salinity and moderate pH/high salinity alkaline floods. These increases are due to the formation of W/0 emulsions in the presence of a univalent electrolyte. Bulk phase experiments of earlier section indicate that the salt concen-... 

The incremental production of acidic oil by moderate pH (buffered) /high salinity alkaline systems occurred by what is believed to be a complete wettability reversal mechanism. Complete wettability reversal is suggested by the magnitude of the measured contact angle, 170° but not by the wettability index of the porous media. The results of the secondary and tertiary buffered floods appear to confirm the experimental results of Cooke et al. (4) the work of these researchers is discussed in a later section. It will be shown that this mechanism is not a direct extension of the emulsification and partial wettability reversal mechanism. 

Aveyard et al. [24,66] have made a more extensive study of the effect of n-alkanes on the foam behavior of a solution of a different surfactant— an aqueous saline solution of AOT (3.8 mM in 0.03 M NaQ). This solution is turbid due to the presence of dispersed lamellar phase as shown in Figure 4.3. The study involved all n-alkanes from hexane to hexadecane together with squalane. Again foam was generated by cylinder shaking with 5 vol.% oil added without pre-emulsification. 

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