Surfactant flooding capillary number

However, all methods of current major interest use the ability of surfactants to disperse one (or more) fluid phase(s) in another. Oil recovery processes in which a dispersion might be used to modify flow patterns include water flooding and high-capillary number (i.e.,... 

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. 

Micellar-polymer flooding relies on the injection of a surfactant solution to lower interfacial tension to ultralow levels, on the order of 10 mN/m. The resulting increase in capillary number allows the recovery of residual oil from porous media. The term micellar is used because the concentrations of injected surfactant solutions are always above their critical micelle concentration. That is, they are always above the concentration at which micelles form. 

This method is also known as micellar flooding, microemulsion flooding, or low tension water fiooding. The primary effect of the use of surfactants is the lowering of the interfacial tension between the driving fluid and the oil. More formally the capillary number, Ac, is... 

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... 

This chapter covers the fundamentals of surfactant flooding, which include microemulsion properties, phase behavior, interfacial tension, capillary desaturation, surfactant adsorption and retention, and relative permeabilities in surfactant flooding. It provides the basic theories for surfactant flooding and presents new concepts and views about capillary number (trapping number), relative permeabilities, two-phase approximation of the microemulsion phase behavior, and interfacial tension. This chapter also presents an experimental study of surfactant flooding in a low-permeability reservoir. 

The main objective of surfactant flooding is to reduce residual oil saturation, which is closely related to capillary number. Therefore, the concept of capillary number is discussed first. Analysis of the pore-doublet model yields the following dimensionless grouping of parameters (Moore and Slobod 1955), which is a ratio of the viscous-to-capillary force ... 

This section discusses how to select the parameters to calculate capillary number. Initially, capillary number was proposed to correlate the residual saturation of the fluid (oil) displaced by another fluid (water) in the two-phase system. In surfactant-related flooding, there is multiphase flow (water, oil, and microemulsion), especially at the displacing front. If we use up/a to define the relationship between capillary number and residual oil saturation, which phase u and p and which o should be used then To the best of the author s knowledge, this issue has not been discussed in the literature. The following is what we propose. 

Chemical flooding involves the injection of a surfactant solution that can cause oil-aqueous interfacial tension to drop from about 30 mN m to near-zero values on the order of 10 -10 mN m , allowing spontaneous or nearly spontaneous emulsification of the oU, with an increase in the capillary number by several orders of magnitude and with greatly increased displacement and recovery of the oil [6, 10,19, 67, 75, 79-87]. The micelles present also help to solubilize the released oil droplets hence, this process is sometimes referred to as micellarflooding. Having mobilized the oil, these processes are even more efficient if the oil droplets are... 

After water flooding, residual oil is believed to be in the form of discontinuous oil ganglia trapped in the pores of rocks in the reservoir. The two major forces acting on an oil ganglion are viscous forces and capillary forces, the ratio of which is represented by the capillary number. At the end of the secondary oil recovery stage, the capillary number is around 10 . To recover additional oil, the capillary number has to be increased to around 10" —10, which can be achieved by decreasing the interfacial tension at the oil/brine interface. Surfactants are used for this purpose. 

The microscopic mobilization efficiency (or the percentage reduction in the residual oil saturation of a secondary waterflood) of tertiary surfactant floods has been experimentally correlated to be a function of the capillary number. 

The propoxy ethoxy sulfonate used by Taugbpl et al. [14] also showed an IFT value close to 10 mN/m towards n-heptane in seawater. Figure 7. Thus, the present PO-EO-surfactant systems are able to lower the IFT between water and oil by a factor of more than three magnitudes in a Type II( —) phase behavior. The corresponding increase in the capillary number suggests that a significant amount of waterflooded residual oil will be recovered by a chemical flood performed in the two-phase region. 

Low Tension Polymer Water Flood. In oil reservoirs, where the critical capillary number is relatively low, a significant amount of waterflooded residual oil can be displaced by surfactants of high efficiency even at two-phase flood conditions. This was demonstrated by the snccessfnl second Ripley surfactant flood pilot test in the Loudon field where approximately 68% of waterflooded residual oil was recovered by injecting a 0.3 PV microemulsion bank [63]. The microemulsion bank was followed by I.O PV of higher viscosity polymer drive. The chemical formnlation consisted of a blend of two PO-EO sulfates. 

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