Alkaline flooding entrapment

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 based on the reaction that occurs between the alkaline water and the organic acids, naturally occurring in some crudes, to produce in-situ surfactants or emulsifying soaps at the oil/water interface. Recent literature (i-J.) summarizes several proposed mechanisms by which alkaline water-flooding will enhance oil recovery. These mechanisms include emulsification and entrapment, emulsification and entrainment, and wettability reversal (oil-wet to water-wet or water-wet to oil-wet). Depending on the initial reservoir and experimental conditions with respect to oil, rock and injection water properties, one or more of these proposed mechanisms may be controlling. 

Alkaline flooding (AF) is a chemical process used in the Petroleum Industry to remove oil from pore walls and to mobilize the mechanically entrapped oil globules or ganglia in porous media. Among all the enhanced oil recovery (EOR) processes, the AF is one of the most complicated and least understood due to its complex oil recovery mechanisms. 

Consequently, such an idea led to the development of a new EOR process called the "first version of Polymer Augmented Alkaline Flooding" (PAAF). In the application of this process an alkaline solution slug is injected to mobilize the residual oil, which is the oil mechanically entrapped and/or sticking on the pore walls. The alkaline solution slug is chased by a fresh polymer slug, which provides the improved mobility control and volumetric sweep efficiency to enhance oil recovery ... 

In the alkaline flood process, the surfactant is generated by the in situ chemical reaction between the alkali of the aqueous phase and the organic acids of the oil phase The surface-active reaction products can adsorb onto the rock surface to alter the wettability of the reservoir rock and/or can adsorb onto the oil-water interface to lower the interfacial tension. At these lowered tensions (1-10 dyne/cm), surface or shear-driven forces promote the formation of stable oil-in-water emulsions or unstable water-in-oil emulsions the nature of the emulsion phase depends on the pH, temperature, and electrolyte type and concentration. These different paths of the surface-active reaction products have created different recovery mechanisms of alkaline flooding. The four alkaline recovery mechanisms which have been cited in the recent literature are (i) Emulsification and Entrainment, (ii) Emulsification and Entrapment, (iii) Wettability Reversal from Oil-to Water-Wet, and (iv) Wettability Reversal from Water- to Oil-Wet. These four mechanisms are similar in that alkaline flooding enhances the recovery of acidic oil by two-stage processes. 

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 emulsification and entrapment mechanism is illustrated in the pressure and production history of the tertiary alkaline flood. 

The results of the tertiary and Ca(0H)2 secondary floods are presented in Figures 13 and 14. In the waterflood, breakthrough of the flood water occurred after injection of 0.6 pore volumes of distilled water. The secondary waterflood recovered 71.7 percent of the original oil in place. In the subsequent tertiary mode alkaline flood, oil appeared in the effluent after 1.2 pore volumes of calcium hydroxide were injected into the waterflooded core. The tertiary oil production was delayed because a finite residence time is required for emulsification of the entrapped residual oil, coalescence of the water-in-oil emulsion and subsequent mobilization of the coalesced droplets into an oil bank. 

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... 

---