Displacement mechanisms alkaline flooding

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... 

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. 

Ultra-low tension In the alkaline flooding of acidic acids, some reduction in interfacial tension (from 30 to approximately 10 1 dynes/cm) is necessary for the emulsification and subsequent mobilization of waterflooded residual oil by the previously discussed phase alteration mechanisms. The residual oil may also be mobilized and produced by a low-tension displacement process which is similar to surfactant flooding if the interfacial tension can be further reduced to ultra-low values (10 to 10 dynes/cm). 

It was determined from dynamic displacement experiments that alkaline flooding of acidic oils with hydroxides of certain divalent cations increased the production and recovery efficiencies above that obtained by alkaline floods with hydroxides of univalent ions with or without high electrolyte concentration. The increased efficiencies resulted from an Emulsification and Coalescence mechanism. 

The chemicals which have been used, or are being used, for alkaline flooding are sodium orthosilicate and sodium hydroxide. Sodium carbonate and sodium tripolyphosphate are not alkaline enough to react with the acids in crude oils. Johnson (6) and Mungan (9) have published reviews of alkaline flooding in which they summarize the proposed mechanisms of oil displacement (Table 2) and some of the important parameters for selection of alkaline flooding candidates (Table 3). These topics are covered in these two publications and will not be discussed further in this paper. 

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