Micellar flooding process

Micellar flooding is a promising tertiary oil-recovery method, perhaps the only method that has been shown to be successful in the field for depleted light oil reservoirs. As a tertiary recovery method, the micellar flooding process has desirable features of several chemical methods (e.g., miscible-type displacement) and is less susceptible to some of the drawbacks of chemical methods, such as adsorption. It has been shown that a suitable preflush can considerably curtail the surfactant loss to the rock matrix. In addition, the use of multiple micellar solutions, selected on the basis of phase behavior, can increase oil recovery with respect to the amount of surfactant, in comparison with a single solution. Laboratory tests showed that oil recovery-to-slug volume ratios as high as 15 can be achieved [439]. 

The works of various investigators such as Gogarty and Tosch (1), Healy and Reed (2), and Davis and Jones (2), have shown that the micellar flooding process can be used effectively to mobilize residual oil in watered-out light oil reservoirs. Many field tests conducted in the U.S. have further proved its effectiveness. However, the economics of the process remain unattractive for implementing the process for tertiary oil recovery. 

Recent works by Holm (A), Pope (2), Sayyouh and Farouq Ali ( ), Enedy and Farouq Ali (2) made significant contributions towards improving the efficiency of the process. The primary objective of this research was to devise a micellar flooding process that is economically as well as technically attractive to the industry, through the use of multiple micellar slugs. 

Improve the efficiency of the micellar flooding process through the use of multiple micellar slugs ... 

Recent research and field tests have focused on the use of relatively low concentrations or volumes of chemicals as additives to other oil recovery processes. Of particular interest is the use of surfactants as CO (184) and steam mobility control agents (foam). Also combinations of older EOR processes such as surfactant enhanced alkaline flooding and alkaline-surfactant-polymer flooding have been the subjects of recent interest. Older technologies polymer flooding (185,186) and micellar flooding (187-189) have been the subject of recent reviews. In 1988 84 commercial products polymers, surfactants, and other additives, were listed as being marketed by 19 companies for various enhanced oil recovery applications (190). 

The efficiency of a micellar slug to recover tertiary oil is largely dependent on its ability to remain a single phase during the flooding process so that the oil may be displaced "miscibly" and hence, completely. However,... 

In the water-flooding process, mixed emulsifiers are used. Soluble oils are used in various oil-well-treating processes, such as the treatment of water injection wells to improve water injectivity and to remove water blockage in producing wells. The same method is useful in different cleaning processes with oil wells. This is known to be effective since water-in-oil microemulsions are found in these mixtures, and with high viscosity. The micellar solution is composed essentially of hydrocarbon, aqueous phase, and surfactant sufficient to impart micellar solution characteristics to the emulsion. The hydrocarbon is crude oil or gasoline. Surfactants are alkyl aryl... 

The structure and thermodynamics of formation of mixed micelles is of great theoretical interest. Micelles are also present and often integrally involved in practical processes. For example, in a small pore volume surfactant flooding process (sometimes called micellar flooding), the solution injected into an oil field generally contains 5-12 weight X surfactant (i) and the surfactant is predominately in micellar form in the reservoir water. In detergency, solubilization can be... 

The micelles present also help to solubilize the released oil droplets hence, this process is sometimes referred to as micellar flooding. The emulsions can be formulated to have moderately high viscosities that help to achieve a more uniform displacement front in the reservoir this uniform front gives improved sweep efficiency. Thus, a number of factors can be adjusted when using a microemulsion system for enhanced oil recovery. These are discussed in detail in Chapter 7. 

Recently we have carried out laboratory tests (17, 18, 19) in which the sodium silicate was added directly to a dilute surfactant solution to recover oil. Such a process would be akin to alkaline flooding processes where a dilute surfactant is formed in-situ. In this case however the crude is lighter and does not contain the natural acids necessary to form surfactants in-situ. Therefore surfactant is injected and protected or enhanced by the sodium silicate such that a low tension waterflood is assured. Such a system is less complex and therefore more widely applicable than micellar/polymer techniques thus filling the void between the alkaline and micellar/polymer EOR processes. 

The major problem experienced in the field to date in chemical flooding processes has been the inability to make contact with residual oil. Laboratory screening procedures have developed micellar-polymer systems that have displacement efiiciencies approaching 100% when sand packs or uniform consolidated sandstones are used as the porous medium. When the same micellar-polymer system is applied in an actual reservoir rock sample, however, the efficiencies are usually lowered significantly. This is due to the heterogeneities in the reservoir samples. When the process is applied to the reservoir, the efiiciencies become even worse. Research is being conducted on methods to reduce the effect of the rock heterogeneities and to improve the displacement efficiencies. 

Polymers are used for mobility control in chemical flooding processes such as micellar-polymer and caustic-polymer flooding and in polymer augmented waterflooding. Selection of a polymer for mobility control is a complex process because it is not possible to predict the behavior of a polymer in porous rock from rheological measurements such as viscosity/ shear rate curves. Polymers used for mobility control are non-Newtonian fluids. Flow characteristics are controlled by the shear field to which the polymer is subjected. Properties of polymers can be measured under steady shear in rheometers. However, in porous rock, it is difficult to define the shear environment a polymer experiences as it flows through tortuous pores. 

Entrapment and mobilization mechanisms at low flow rates and low interfacial tension can also control the recovery obtained by tertiary methods. In micellar flooding, for example, high ratios of viscous to capillary forces arise at field flow rates when interfacial tensions are very low. Development of a continuous oil bank having significant mobility requires that discontinuous oil be mobilized to form a continuous bank which gathers more residual oil as it advances. Interfacial tensions may exist or develop between the micellar bank and the oil, or between the micellar fluid and the aqueous polymer bank used to push the micellar fluid. Entrapment of oil by the micellar bank, or of micellar fluid by the polymer bank would eventually cause the process to fail. 

Water-soluble polymers are used in many oilfield operations. These include drilling, polymer-augmented water flooding, and various enhanced oil recovery processes such as alkaline and micellar flooding. In enhanced oil recovery (EOR), the basic idea behind using these polymers is to reduce the mobility of the aqueous phase and, consequently, to improve the sweep efficiency. 

An alternative to this process is low (<10 N/m (10 dynes /cm)) tension polymer flooding where lower concentrations of surfactant are used compared to micellar polymer flooding. Chemical adsorption is reduced compared to micellar polymer flooding. Increases in oil production compared to waterflooding have been observed in laboratory tests. The physical chemistry of this process has been reviewed (247). Among the surfactants used in this process are alcohol propoxyethoxy sulfonates, the stmcture of which can be adjusted to the salinity of the injection water (248). 

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 is a technically well-developed process. Phase compositional aspects of microemulsion design are relatively well understood, and several technically successful field trials have been carried out. Micellar-polymer floods can be designed and carried out with a good chance of success. However, the process is too expensive. This high cost is due primarily to the high concentrations of synthetic surfactants required. The problem is further compounded because these synthetic surfactants are made from petrochemicals, a fact that ties their price to the price of crude oil. 

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