Crude oil caustic systems

Figure 2. Spontaneous emulsification in Long Beach crude oil-caustic system (a) initiation of fingering action and formation of water in oil droplets (h) termination of fingering action and formation of water in oil droplets (c) threads of oil droplets (d) formation of very thin strings and appearance of oil droplets in aqueous phase and (e) appearance of buds of oil at the oil-aqueous interface...

Figure 5. Kinetics of coalescence for nonequilihrated sample of Long Beach crude oil-caustic system...

The interfacial tension for the crude oil-caustic system was measured by the spinning drop technique. The instrument used is similar in design to the one reported by Schechter and Wade (2). 

Figure 7. Kinetics of coalescence for equilibrated samples of Huntington Beach crude oil-caustic systems...

The very low interfacial tensions reported for many crude oil-caustic systems should permit substantial reduction of residual oil saturation by the mobilization of trapped oil. We have discussed earlier that crude oil-caustic tension is low initially where reactants meet at a fresh interface but the interfacial tension increases as reaction products diffuse into the bulk phases. The technique of determining micellar aggregate size distributions could be used to study the diffusion of the reaction products into the aqueous phase. 

Caustic Waterflooding. In caustic waterflooding, the interfacial rheologic properties of a model crude oil-water system were studied in the presence of sodium hydroxide. The interfacial viscosity, the non-Newtonian flow behavior, and the activation energy of viscous flow were determined as a function of shear rate, alkali concentration, and aging time. The interfacial viscosity drastically... 

This paper presents observations on the difference in behavior of emulsification processes which can occur during surfactant and caustic flooding in enhanced recovery of petroleum. Cinephotomicrographic observations on emulsion characteristics generated at the California crude oil-alkaline solution interface as well as in the Illinois crude oil-petroleum sulfonate system are reported. The interdroplet coalescence behavior of oil-water emulsion systems appear to be quite different in enhanced oil recovery processes employing various alkaline agents as opposed to surfactant/polymer systems. 

In this paper we report first the spontaneous emulsification mechanisms in the petroleum sulfonate and caustic systems. This is followed by the kinetics of coalescence in alkaline systems for both the Thums Long Beach (heavy) crude oil and the Huntington Beach (less viscous) crude oil. Measurements of interfacial viscosity, interfacial tension, interfacial charge and micellar aggregate distributions are presented. Interrelationships between these properties and coalescence rates have been established. 

Figure 5 shows the kinetics of coalescence for the caustic (0.05M NaOH, 1.0% NaCl), Thums Long Beach (heavy) crude oil system, with and without the co-surfactant n-hexanol (0.5%). This data shows that the mean droplet volume (which is proportional to 1/number of droplets) increases with time. The addition of hexanol alters the kinetics of interdroplet coalescence to a level that the emulsion almost totally coalesces within ten days. 

A series of experiments were conducted to determine the emulsion stability in caustic systems. Figures 6 and 7 show data for the kinetics of coalescence and hence emulsion stability for the crude oil from Huntington Beach (Lower Main Zone), California (oil gravity of 23°API and oil acid number of 0.65). Figure 6 shows data for a nonequilibrated system and for a very low concentration of NaOH (0.003%) and 1% NaCl. This emulsion is unstable. Figure 7 shows data for two different concentrations of... 

Figure 8 shows the values of electrophoretic mobility and interfacial tension as a function of the NaOH concentration for the Long Beach crude oil which has been equilibrated with the alkaline solution. This figure shows that the electrophoretic mobility increases and then decreases with increasing caustic concentration. It should be noted that the maximum in electrophoretic mobility appears to correspond to a minimum in interfacial tension. This finding is consistent with our recent results for surfactant systems (6) and those of Shah and Walker (21). 

The interfacial tension values reported for the caustic system in Figure 8 are comparable to the values reported recently in reference (22). Our experiments which have been conducted at a room temperature of about 25°C show that 0.1 to 0.4 weight percent concentrations of NaOH and 1.00 weight percent NaCl can lower the interfacial tension between the aqueous solution and the crude oil substantially below a value of 0.01 dynes/cm or that required for emulsification. We have previously discussed the stability of these emulsions (Fig. 5). In the experiments run on fired Berea cores, it was reported that a concentration of 0.1% NaOH and 1% NaCl in the caustic crude oil system resulted in a drastic reduction in residual oil saturation. The details of these tests are given in reference (22). 

Figure 13 exhibits both interfacial tension and electrophoretic mobility for the Huntington Beach Field crude oil against sodium orthosilicate containing no sodium chloride. The interfacial tension values are observed to be higher for the non-equilibrated sample in this case than for the caustic system reported in Figure 12. The minimum interfacial tension of 0.01 dynes/cm occurs at about 0.2% sodium silicate as opposed to a value of less than 0.002 dyne/cm at about 0.06% NaOH. It is interesting to note, however, that the maximum electrophoretic mobility is the same for the two systems. Once again, it should be noted that a maximum in electrophoretic mobility does not correspond to a minimum in interfacial tension for those samples which contained no sodium chloride.

Figure 16. Natural crude oil surfactant micellar aggregate size distributions for Long Beach crude/caustic system. The aqueous phase containing 0.05M NaOFI without hexanol (0) and with 0.50% hexanol ( ).

Preliminary results on the kinetics of coalescence of both the Long Beach and the Huntington Beach crude oil droplets in caustic systems have been presented. 

Previous work (1) in core floods with the system, Huntington Beach Crude vs. 0.5% Na SiO plus 0.75% NaCl, showed channeling of the crude oil during the injection of the caustic slug (Figure 6). The channeling phenomena along with the fact that emulsions were not observed until after 95% of the recovered oil was produced, could have lead to lower oil recovery efficiencies. To... 

In a petroleum sulfonate/isobutanol/dodecane/brine system, there are two regions of ultralow interfacial tension (IFT), one at low surfactant concentrations (0.1-0.2%) and the other at higher surfactant concentrations (4 to 10%). In the low concentration range, the oil/brine/surfactant/alcohol system is a two-phase system, whereas at high surfactant concentrations, it becomes a three-phase system in which a middle phase microemulsion is in equilibrium with excess brine and oil. For low surfactant concentration systems, we have shown that the ultralow IFT minimum corresponds to the onset of micellization and partition coefficient of surfactant near unity. This correlation was observed for the effect of surfactant concentration, salt concentration and oil chain length on the interfacial tension. The minimum in interfacial tension corresponds to a maximum electrophoretic mobility of oil droplets. This correlation was also observed for the effect of caustic on several crude oils. 

Figure 6 shows the effect of surfactant concentration on interfacial tension and electrophoretic mobility of oil droplets (14). It is evident that the minimum in interfacial tension corresponds to a maximum in electrophoretic mobility and hence in zeta potential at the oil/brine interface. Similar to the electrocapillary effect observed in mercury/water systems, we believe that the high surface charge density at the oil/brine interface also contributes to lowering of the interfacial tension. This correlation was also observed for the effect of caustic concentration on the interfacial tension of several crude oils (Figure 7). Here also, the minimum interfacial tension and the maximum electrophoretic mobility occurred in the same range of caustic concentration (17). Similar correlation for the effect of salt concentration on the interfacial tension and electrophoretic mobility of a crude oil was also observed (18). Thus, we believe that surface charge density at the oil/brine interface is an important component of the ultralow interfacial tension.

The crude oil system used for our work was the LMZ (Lower Main Zone) S-47 variety from Huntington Beach, California. This crude oil has an acid number of 0.65 mg KOH/gm sample which makes it particularly amenable to caustic flooding techniques. The bulk viscosity measured at room temperature was 108 cp. The API gravity for this crude oil is 23.5°. The standard caustic aqueous phase was 0.15% (wt) sodium orthosilicate plus 0.75% (wt) sodium chloride in double distilled water. At this concentration, the aqueous phase has a pH of 11.7. 

In conclusion, we have observed the individual and combined effects that the heavy, naturally occurring asphaltic components have upon the interfacial activity and structure of an acidic crude oil-aqueous alkaline system. The subsequent film formation that these components exhibit when contacted with a caustic phase suggests the presence of a stabilizing barrier that may impede coalescence of viscous emulsions formed in situ during flooding processes. 

To minimize aqueous chloride corrosion in the overhead system of crude towers, it is best to keep the salt content of the crude oil charge as low as possible, about 4 ppm. Another way to reduce overhead corrosion would be to inject sodium hydroxide into the crude oil, downstream of the desalter. Up to 10 ppm caustic soda can usually be tolerated. 

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