Alkaline interfacial tension

Figure 5. Comparison of alkaline interfacial tension reduction vs, pH of Illinois crude, 0.25% Petrostep 450, 1.5% N l. (Reproduced, with permission, from Ref. 17. Copyright 1980, Society of Petroleum Engineers of AIME.)...

In buffered surfactant-enhanced alkaline flooding, it was found that the minimum in interfacial tension and the region of spontaneous emulsification correspond to a particular pH range, so by buffering the aqueous pH against changes in alkali concentration, a low interfacial tension can be maintained when the amount of alkali decreases because of acids, rock consumption, and dispersion [1826]. 

The dynamic interfacial tension behavior of reacting acidic oil-alkaline solutions has been studied for both an artificially acidified synthetic oil and a real crude oil at various concentrations [131,132] with either a drop volume tensiometer or a spinning drop tensiometer. 

S. D. Ball, V. Homof, and G. H. Neale. Transient interfacial tension behavior between acidic oils and alkaline solutions. Chem Eng Com-mun, 147 145-156, May 1996. 

C. I. Chiwetelu, V. Homof, G. H. Neale, and A. E. George. Use of mixed surfactants to improve the transient interfacial tension behaviour of heavy oil/alkaline systems. Can J Chem Eng, 72(3) 534-540, June 1994. 

Effect of pH. Interfacial tensions between heavy crude oils and alkaline solutions were measured at temperatures up to 180°C by Mehdizadeh and Handy T341. They observed that tensions increased with an increase in temperature. However, recovery efficiencies obtained at high temperatures were comparable to those obtained at lower temperatures, apparently because the ease of emulsification at high temperatures counteracted the increase in tens i on. 

Effect of Ca2. In many reservoirs the connate waters ontain substantial quantities of divalent ions (mostly Ca . In alkaline flooding applications at low temperatures, the presence of divalent ions leads to a drastic increase in tensions r35,36]. Kumar et al. f371 also found that Ca and Mg ions are detrimental to the interfacial tensions of sulfonate surfactant systems. Detailed studies at elevated temperatures appear to be non-existent. 

Chan, M. Yen, T.F. Role of Sodium Chloride in the Lowering of Interfacial Tension Between Crude Oil and Alkaline Aqueous Solution, Fuel, 1981, 60, 552. 

In acid solution as far as Ph = 5 the interfacial tension is constant but with increasing alkalinity it falls. In the case of fatty acids the tension becomes vanishingly small when the Ph exceeds 8 and the acid dissolves in the alkali in the form of micelles (see Ch. ix). 

For the buffer solution Ph = 5 6 the variation of interfacial tension with the strength does not exceed the experimental error, but in the more alkaline solution we must conclude that either sodium ions or phosphate ions (or both) are positively adsorbed according to the equation... 

Alkali compounds are used in the Surtek process to reduce the interfacial tension between the oil phase and the aqueous phase. In addition, an alkaline agent neutralizes rock and clay surfaces and reduces the amount of exchangeable calcium and magnesium ions from the soil surface. Both of these functions reduce surfactant and polymer adsorption into the soil matrix. 

Octadecanol was recrystallized from hexane after fractionation by vacuum distillation, and its purity was checked by gas-liquid chromatography. Dodecylammonium chloride was recrystallized from a mixture of ethanol and water, and its purity was confirmed by the fact that it had no minimum near the critical micelle concentration on the surface tension vs concentration curve. Hexane was distilled after passing through an activated alumina column. Water was distilled from alkaline permanganate solution of distilled water after refluxing for one day. The purity of hexane and water was confirmed by the value of the interfacial tension between them. 

Interfacial properties. The effect of the aqueous phase on interfacial tensions of irradiated TBP-diluent/nitric acid systems was measured (142). For neutral and acidic aqueous phase, the interfacial tension was similar for fresh and irradiated systems, but in contact with 0.6 mol L 1 NaOH solution, which is representative of alkaline treatment, a decrease of interfacial tension was observed. 

Some authors have studied the effects of treatment with solid sorbents. Activated alumina was found to be very effective for secondary cleanup after alkaline scrubbing to remove compounds responsible for the decrease of interfacial tension and the complexing of plutonium. The drying of the solvent improves the capacity of activated alumina (102, 150, 151). 

Several generic kinds of results are pertinent to the properties of dispersions. The surfactant solutions formulated to stabilize microemulsions, and some kinds of macroemulsions, can exhibit marked dynamic interfacial tension behaviour. Figure 3.14 shows an example in which a series of commerical surfactant additions are made to a system containing crude oil and a base. Under alkaline conditions the interfacial tension is already dynamic due to the saponification of natural surfac-... 

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. 

Alkaline flooding is an old concept, first patented by Atkinson (48) in 1927. Hydroxide ion in an alkaline solution reacts with acidic components present in some crude oils to produce petroleum soaps, which are generally sodium salts of carboxylic acids. These petroleum soaps are capable of adsorbing at the oil-water interface and lowering interfacial tension. Crude oils suitable... 

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. 

In 1931 Peters (54) made what he describes as the first measurements of the strength of ionization at an interface. He measured the interfacial tension of long-chain acids and amines at the interface between benzene and water, the latter containing various buffering salts. The change, he found, of the interfacial tension due to appreciable ionization, in the case of the carboxyl head occurs at about 3.0 pH units on the alkaline side, and in the case of the amine some 4.0 pH units to the acid side of the point at which the corresponding water-soluble acid and base would commence to ionize in aqueous solution. ... 

A fundamental chemical process is surfactant flooding in which the key mechanism is to reduce interfacial tension (IFT) between oil and the displacing fluid. The mechanism, because of the reduced IFT, is associated with the increased capillary number, which is a dimensionless ratio of viscous-to-local capillary forces. Experimental data show that as the capillary number increases, the residual oil saturation decreases (Lake, 1989). Therefore, as IFT is reduced through the addition of surfactants, the ultimate oil recovery is increased. In alkaline flooding, the surfactant required to reduce IFT is generated in situ by the chemical reaction between injected alkali and naphthenic acids in the... 

Capillary number can be increased by increasing velocity or by lowering interfacial tension by snrfactant or alkaline flooding. From Table 7.8, it seems that there is no distinct difference in the magnitnde of critical capillary nnmber based on these different approaches. However, we should note that for most of the tests in Table 7.8 the capillary nnmber was increased by increasing flow velocity. 

Alkalis react with naphthenic acid in crude oil to generate soap. The soap, an in situ generated surfactant, reduces the interfacial tension between the alkaline solution and oil. It is intuitive to infer that the main mechanism in alkaline flooding is low IFT. 

In describing surfactant phase behavior or activities, Chinese methodology is to use interfacial tension (probably their philosophy is to rely on IFT measurement). Therefore, their activity map is to show the IFT at different surfactant and alkaline concentrations. Figure 12.6 is an example of such an activity map. In this figure, the region of ultralow IFT (10 mN/m) is marked. 

At the concentrations of alkali above that required for minimum interfacial tension, the systems become overoptimum. The excess alkali plays the same role as excess salt. When synthetic surfactants are added, the salinity requirement of alkaline flooding system is increased. NEODOL 25-3S is such a synthetic surfactant used by Nelson et al. (1984). Figure 12.4, shown earlier, is a composite of three activity maps for 0, 0.1, and 0.2% of NEODOL 25-3S as a synthetic surfactant for 1.55% sodium metasilicate with Oil G at 30.2°C. We can see in the figure that without the synthetic surfactant, the active region of this system is below the sodium ion concentration supplied by the alkali. However, with 0.1 and 0.2% of NEODOL 25-3S (60% active) present, the active region is above the sodium ion concentration supplied by the alkali, so additional sodium ions must be added to reach optimum salinity. 

---