Alkaline flooding alkalis used

Alkaline flooding is also called caustic flooding. Alkalis used for in situ formation of surfactants include sodium hydroxide, sodium carbonate, sodium orthosilicate, sodium tripolyphosphate, sodium metaborate, ammonium hydroxide, and ammonium carbonate. In the past, the first two were used most often. However, owing to the emulsion and scaling problems observed in Chinese field applications, the tendency now is not to use sodium hydroxide. The dissociation of an alkali results in high pH. For example, NaOH dissociates to yield OH" ... 

Alkaline Floods. Alkaline floods, typically using sodium hydroxide, generate surface active products by an in-situ chemical reaction between the injected alkali and the organic acids of the crude. Four possible mechanisms [95] are responsible for the recovery of oil by alkaline floods (1) emulsification and entrainment, (2) emulsification and entrapment, (3) wettability reversal from oil-wet to water-wet, and (4) wettability reversal from water-wet to oil-wet. One example in the literature of wettability alteration by alkali [96] was reported for an offshore field in the Gulf of Mexico fhat had a low recovery factor from primary production. The wettability of this reservoir was found, using the... 

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. 

This section compares different alkalis used in alkaline flooding and discussed their application advantages and disadvantages. 

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. 

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. 

ALKALINE FLOODS - HUNTINGTON BEACH FIELD CRUDE IN BEREA SANDSTONE CORES USING 0.5 PV OP ALKALI INJECTION... 

Mechanistic interpretations The results of the dynamic and equilibrium displacement experiments are used to evaluate and further define mechanisms by which alkaline floods increase the displacement and recovery of acidic oil in secondary mode and the tertiary mode floods. The data sets used in the mechanistic interpretations of alkaline floods are (a) overall and incremental recovery efficiencies from dynamic and equilibrium displacement experiments, (b) production and effluent concentration profiles from dynamic displacement experiments, (c) capillary pressure as a function of saturation curves and conditions of wettability from equilibrium displacement experiments, (d) interfacial tension reduction and contact angle alteration after contact of aqueous alkali with acidic oil and, (e) emulsion type, stability, size and mode of formation. These data sets are used to interpret the results of the partially scaled dynamic experiments in terms of two-stage phase alteration mechanisms of emulsification followed by entrapment, entrainment, degrees and states of wettability alteration or coalescence. 

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. 

The data from these tests show that sodium orthosilicate is more effective than sodium hydroxide in recovering residual oil under the conditions studied, both for continuous flooding and when 0.5 PV of alkali was injected. The mechanisms through which sodium orthosilicate produced better recovery than sodium hydroxide in this system have not been completely elucidated. Reduction in interfacial tension is similar for both chemicals, so other factors must play a more important role. Somasundaran (26) has shown that sodium silicates are more effective than other alkaline chemicals in reducing surfactant adsorption on rock surfaces. Wasan (27,28) has indicated that there are differences in coalescence behavior and emulsion stability which favor sodium orthosilicate over sodium hydroxide. Further work is being done in this area in an attempt to define the limits of physically measurable parameters which can be used for screening potential alkaline flooding candidates. 

Table 5. Alkaline Floods - Huntington Beach Field Crude in Berea Sandstone Cores Using 0.5 PV of Alkali Injection... 

For oil displacement purposes, alkali can be co-injected with any displacing agents except an acid or carbon dioxide. For example, aUcaline-polymer (AP), alkaline-surfactant (AS), aUcaline-gas, alkaline-steam, aUcaline-hot water, and more can be used. This chapter discusses alkaline-surfactant flooding. 

Low tension waterflooding is a method intermediate between alkaline and micellar/polymer technology. The LTWF employs a dilute surfactant to reduce IFT and mobilize residual oil. A few field trials (26-29) of this process have been tried with mixed success. None of these trials however employed sodium silicates in any part of the flood design. Instead, other alkalis such as sodium carbonate and sodium tripoly- phosphate were used. Some of the reasons proposed for the limited success in these trials were 1) high consumption of the sacrificial agents, leaving the surfactant unprotected, 2) poor sweep of the pay zone, 3) limited mobility control and lower than expected displacement efficiency. Recent work published and obtained in our laboratories has shown that sodium silicates may help to overcome some of these problems better than other alkalis. 

Using an anion exchange membrane instead of a liquid caustic alkali electrolyte in an alkaline fuel cell allows avoids problems of leakage, carbonation, precipitation of carbonate salts, and gas electrode flooding, increasing the volumetric energy density. It appears that the anion exchange membrane fuel cells (AEMFCs) have the potential to succeed in portable applieations [92,93]. 

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