Slug, micellar

As a test, surfactant slug flow experiments were performed in clayey sandpacks with and without the injection of a desorbent behind the micellar slug. Results show that a substantial decrease in surfactant retention is obtained in calcic environment by such an additive. Likewise, the ethoxylated cosurfactant in the micellar slug can be remobilized simultaneously with sulfonatewithout any change in its ethylene oxide distribution. The application of the RST to sulfonate/ ethoxylated alkylphenol mixtures explains semi-quantitatively the relationship between their properties and composition. 

A typical sequence followed in this test series consists in injecting (1) a micellar slug of one pore volume of aqueous solution of 4% of the preceding pseudobinary system (2% sulfonate/2% Genapol) (2) a slug of desorbent solution corresponding to a fixed amount of additive (e.g. equal to 1 PV at a concentration of 0.5 %) (3) at least 1.5 PV of brine with no additive. 

Reference tests were also performed in the absence of any desorbent (Tests 1 and 2 in Table III). Likewise, the propagation of each desorbent was examined separately, without any prior micellar slug injection. The effluents were sampled for analysis by a fraction collector. 

To mark the displacement front, 150 ppm of sodium iodide was incorporated in the surfactant micellar slug. This tracer can easily be detected in effluents with a UV detector at 229 nm. 

Figures 5 and 6 show that the concentration of the two surfactants in the effluents increases simultaneously with the production of the desorbent, which confirms the mixed micellization mechanism described above. Figure 5, where the three additives are produced lately, illustrates the phenomenon particularly well. At the lower pH corresponding to strong adsorption conditions for sulfonate (test 4), the one pore-volume micellar slug would have been entirely consumed by the medium in the absence of any desorbent.

Surfactant Transport in an Adsorbent Porous Medium. Chromatographic Aspects A first observation was made in all the tests in Table III. The breakthrough of both surfactants from the micellar slug always occurs simultaneously without any chromatographic effect (Figures 5 and 6). This stems both from the chemical nature of the two products selected and also from the fact that the injected concentration is much greater than the CMC of their mixtures. 

Comparison Theoretical Equilibrium Calculations and Results of Circulation Tests in Porous-Media To make this interpretation more quantitative, the regular solution theory (RST) was applied to sulfonate/desorbent dynamic equilibria reached inside porous media by using the approach described above. In so doing, we assumed that the slugs injected were sufficiently large and that a new equilibrium was reached at the rear of micellar slug in the presence of desorbent. 

Calculations were made at the desorbent concentrations used in Tests 3,6,7 and 8 in Table HI. Table IV below gives the respective adsorptions of sulfonate and desorbent as well as their equilibrium concentration. A comparison with the corresponding experimental values in Table HI shows good agreement with regard to sulfonate from the micellar slug. On the other hand, losses of desorbent are systematically underestimated. This shows that the assumption of the independent adsorption of both surfactants on the solid is incorrect and that presumably cooperative adsorption of desorbent and sulfonate takes place. Accordingly the model used needs to be improved. 

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. 

Process efficiency, in this study, is defined as the tertiary oil recovery per unit volume of the slug injected. This refers to the efficiency of an oil-rich slug. Economic recovery efficiency varies from slug to slug due to variations in the surfactant content. it should be noted that the micellar slugs were formulated with an effort to keep the cost a minimum. 

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,... 

Formulate efficient micellar slugs for the tertiary recovery of three light oils viz. Bradford crude, Bonnie Glen crude, and Provost crude ... 

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

A micellar flood was then started with the injection of the micellar slug, polymer buffer, and the drive water in succession, at a rate of 1.3 m/day. Two types of polymers - polyacrylamide polymer (Dow Pusher 700) and Xanthan Gum polymer (Kelzan XC) - were used as the polymer buffers. Sodium chloride brine (1%) was used as the drive water. Effluent was collected and analyzed for surfactant content using the IR and UV techniques. 

Table III. Tertiary Recovery with Single Micellar Slugs...

Figure 7. Effect of Micellar Slug Size on the Oil Recovery Efficiency of Micellar Slug B4...

Micellar Slug Total Size, Slug % pv Tertiary Recovery. % oil in place... 

Graded Composite Slugs. In graded micellar slugs, two or more slugs are injected so that a gradation starts with... 

Small micellar slugs (2-5% pv) can recover 3 to 15 times their volume of waterflood residual oil. Final oil saturation was reduced to 0.02% pv for 2% pv slug size and,0.01% pv for 5% pv slug size. 

Figure 9. Production History of 5% PV Micellar Slug B4 and 50% PV Buffer Injected at 1.41 m/day...

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