Alkaline flooding acid number

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... 

Figure 10.19 shows the reduction in residual oil saturation by alkaline flood versus different acid numbers. These data are calculated from those presented by Ehrlich and Wygal (1977), so are the data in Figures 10.20 through 10.22. The alkali used was 0.1% NaOH. Figure 10.19 shows that those two variables were not correlated. 

From the previous discussions, we can see that ultralow IFT cannot be reached in alkaline flooding. The incremental oil recovery is not correlated with the IFT or crude acid number. The low IFT mechanism may not be the dominant mechanism. However, a reasonably low IFT is required for emulsification to occur, which is another proposed mechanism and summarized in the previous section. 

In this hypothetical case, the objective is to provide detailed procedures to simulate an alkaline flood. The concentrations of formation water (initial water) and injected water, with some calculated concentrations, are shown in Table 10.8. The initial formation water pH is 8.1 the acid number is 0.81 g KOH/g oil and the initial water and oil saturations are 0.383 and 0.617, respectively. The task is to set up a UTCHEM alkaline simulation model based on these data. 

Apparently, higher acid number of a given crude, either by nature or due to the addition of known acid, would lower its interfacial tension. However, Cooke, Williams, and Keledzne (4) found that although in-situ oxidation with air further increases the acid number of a given crude, this artificially-made high acid number crude could not be successfully flooded with alkaline water. 

The decreases in the water relative permeabilities of the high pH/high salt alkaline floods are directly contrasted with the increases in the relative permeabilities to water at the end of the moderate pH/high salt flood (compare the end point relative permeabilities column in Table 2). The increased permeability to water is believed to be caused by the formation of rigid interfacial films (which increases the resistance to flow in oil filled pores) and by the oil-wet conditions (under which water flows in the less restrictive flow paths). Such a reduction in permeability, which has been used to indicate the existence of a low tension mechanism (18), is not a valid low tension index since the interfacial tension minimum is only 3.5 dynes/cm and the capillary number is 1 x 10" for the buffered alkali/salt-oleic acid system. 

Recovery of acidic oils with alkaline agents by an emulsification and coalescence mechanism Calcium hydroxide [Ca(0H)2] was used to verify the emulsification and coalescence concept since, as suggested by the theoretical and experimental evidence of an earlier section, the carboxylic salts of divalent ions form unstable emulsions of water-in-oil. The emulsification and coalescence concept was quantitatively verified by secondary and tertiary flooding of partially oil-saturated sandpacks. A tertiary chemical flood with Ca(0H)2 (pH = 12) recovered 44 percent of the waterflood residual oil from a 3.5-darcy Ottawa sandpack the oil had an acid number of 2 and a viscosity of 1.5 cp. A secondary caustic flood with Ca(0H)2 (pH = 12.32) recovered 82.3 percent of the original oil in place from a 0.25-darcy Ottawa sandpack the oil phase in this secondary flood had the same physical and chemical properties as the oil phase used in the tertiary mode flood. It should be noted that the microscopic mobilization efficiencies of these... 

It also reduces adsorption of the (mostly anionic) surfactant on the reservoir rock, essentially by enhancing the negative surface charge. In some cases (alkaline-polymer floods), where there are high levels of saponifiable crude oil acids present in the crude oil (high acid number) added surfactant is not even required. The polymer is present to assist in mobility control and to ensure that the injected chemical slug remains intact and promotes the formation of an oil bank ahead of it. 

The general applicability of these ideas was perhaps first pointed out in the classic articles of Flood and Forland (1947) where the stability properties of a wide variety of oxyanions were correlated with the nature of the cation. Since the decomposition reaction in such cases can be viewed as the production of a smaller or more basic fragment ion plus a more molecular species, the reaction obviously will be enhanced by a more acidic or polarizing cation. For example, the stability of the COs " ion with respect to decomposition to oxide and CO2 decreases with a decrease in atomic number and hence size in either the alkali metal or the alkaline earth metal series, whereas the stability progressively decreases even more with the smaller ions Mg +, Mn +, Cd +, Pb +, Ag+, Zn +, and Fe +. Of course, the relative stabilities of the product oxides must also be considered in a quantitative comparison. Electrostatically the process can be viewed as a competition between the formation of the more stable oxide lattice (plus CO2) and the lower lattice energy of the carbonate plus the bond energy associated with CO2 + CO,3. The elimination of oxide plus SO3... 

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