Alkaline-polymer flooding

In alkaline-polymer flooding, in addition to the polymer mobihty control effect, the precipitation (e.g., Ca(OH)2 and Mg(OH)2) caused by alkah also helps to increase sweep efficiency. Precipitates formed by alkalis may be able to flow through pores without blocking any flow, or reduce both oil and water permeabilities. However, precipitates combined with polymer can effectively reduce water permeability because polymer is in the water phase. 

To establish a baseline for the alkaline-polymer flooding, the operator used several empirical correlations and reservoir simulation to estimate the water-flood recovery factor, which was 50%. To study residual oil saturahon distribution, the operator used several approaches such as pressure coring, C/O logging, core wafer, and waterflood performance analysis. Finahy, all data were integrated into a simulahon model to output the residual oil saturation distribuhon. The average residual oil saturahon was 0.33. The gas cap shrank and existed only in the north area to Wells X19 and X35. This area was far away from the AP flooding area so that it was not affected by AP. 

Chen, Z.-Y., Sun, W., Yang, H.-J., 1999b. Mechanistic study of alkaline-polymer flooding in Yangsanmu Field. Journal of Northwest University (Natural Science Edition) 29 (3), 237-240. 

Potts, D.E., Kuehne, D.L., 1988. Strategy for alkaline polymer flood design with Berea and reservoir-rock corefloods. SPERE 3 (4), 1143-1152. 

Yang, P.-H., et al., 1992. Oil recovery mechanisms of alkaline/polymer flooding. Paper presented at the Second and Tertiary Recovery Symposium, Chengdu. 

Cosurfactant-Enhanced Alkaline/Polymer Floods for Improving Recovery in a Fractured... 

COSURFACTANT-ENHANCED ALKALINE/POLYMER FLOODS FOR IMPROVING RECOVERY IN A FRACTURED SANDSTONE RESERVOIR... 

Potts, D. E. and D. L. Kuehne, Strategy for Alkaline/Polymer Flood Design with Berea and Reservoir-Rock Corefloods, SPE Res. Eng. 3, 1,143-1,152 (1988). 

It also reduces adsorption of the (mostly anionic) surfactant on the reservoir rock, essentially by enhancing the negative surface charge. In some cases (alkaline-polymer floods), where there are high levels of saponifiable crude oil acids present in the crude oil (high acid number) added surfactant is not even required. The polymer is present to assist in mobility control and to ensure that the injected chemical slug remains intact and promotes the formation of an oil bank ahead of it. 

The focus of more recent work has been the use of relatively low concentrations of additives in other oil recovery processes. Of particular interest is the use of surfactants (qv) as CO2 (4) and steam mobiUty control agents (foam). Combinations of older EOR processes such as surfactant-enhanced alkaline flooding and alkaline—surfactant—polymer flooding show promise of improved cost effectiveness. 

Chemical EOR methods are based on the injection of chemicals to develop fluid or interfacial properties that favor oil production. The three most common of these methods are polymer flooding, alkaline flooding, and surfactant flooding. 

The state of the art in chemical oil recovery has been reviewed [1732]. More than two thirds of the original oil remains unrecovered in an oil reservoir after primary and secondary recovery methods have been exhausted. Many chemically based oil-recovery methods have been proposed and tested in the laboratory and field. Indeed, chemical oil-recovery methods offer a real challenge in view of their success in the laboratory and lack of success in the field. The problem lies in the inadequacy of laboratory experiments and the limited knowledge of reservoir characteristics. Field test performances of polymer, alkaline, and micellar flooding methods have been examined for nearly 50 field tests. The oil-recovery performance of micellar floods is the highest, followed by polymer floods. Alkaline floods have been largely unsuccessful. The reasons underlying success or failure are examined in the literature [1732]. 

Alkali/polymer flooding Alkali/surfactant/polymer flooding Alkaline-assisted thermal oil recovery Alkaline steamflooding Polymer-assisted surfactant flooding Water-alternating gas technology... 

The use of chemicals to coax more oil out of the ground has been investigated for many years. Chemically enhanced methods are of three major types (1) polymer flooding (2) surfactant flooding and (3) alkaline flooding. 

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. 

Many of the basic concepts of micellar-polymer flooding apply to alkaline flooding. However, alkaline flooding is fundamentally different because a surfactant is created in the reservoir from the reaction of hydroxide with acidic components in crude oil. This reaction means that the amount of petroleum soap will vary locally as the water-to-oil ratio varies. The amount of petroleum soap has a large effect on phase behavior in crude-oil-alkali-surfactant systems. 

Phase Behavior. The use of phase-behavior diagrams in surfactant-enhanced alkaline flooding is more complicated than in micellar-polymer flooding for several reasons. One reason is that phase behavior is very sensitive to the water-to-oil ratio employed. From surfactant mixing rules, varying the amount of oil present will vary the amount of petroleum soap... 

As the presence of multivalent salts normally results in flocculation of the polymers used in chemical-assisted EOR, the introduction of a monovalent alkaline solution has been employed. As a separate downstream slug, alkaline solutions are normally used as sacrificial materials to obtain synergistic effects with surfactant and polymer flooding methods. Alkaline materials that... 

Although alkaline flooding only is not conducted as often as polymer flooding or surfactant flooding, alkaline injection is conducted together with surfactant and polymer injection. Simulation of alkaline flooding is very difficult because of complex chemical reactions. These complex reactions include at least the following ... 

When alkaline flooding is combined with other methods, such as polymer flooding, surfactant flooding, hydrocarbon gas injection, or thermal recovery, much better effects will be obtained. 

The theories of alkaline flooding and polymer flooding alone are discussed in their respective chapters. This chapter focuses on the interaction and synergy between alkali and polymer. It also presents a field application. 

FIGURE 11.6 Comparison of residual oil recovery factors in alkaline flood, polymer flood, and any combination of these two floods. Source Krumrine and Falcone (1983). 

The synergy between alkaline and polymer flooding may be summarized as... 

Core flood tests were used to compare polymer flood only and alkaline-polymer performance. To model in situ oil/water viscosity ratio correctly, the operator mixed the crude oil with kerosene at a ratio of 100 26. Single-, double-, and triple-column tests were conducted. In the single-column tests, polymer flood increased sweep efficiency over waterflood by 5.6 to 9.77%, and AP flood increased by 13.7 to 19.3%. On average, AP outperformed polymer flood by 8.8%. In the double- and triple-column tests, AP recovery factors were about 18 to 20% higher than waterflood recovery factors. Half of the incremental recovery came from the low permeability column. 

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. 

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