Salinity requirement diagrams

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. 

Salinity Requirement Diagrams. Maximum solubilization parameter occurs very close to the salinity at which maximum core-flood oil... 

To construct a salinity requirement diagram, 5 to 10 different brine salinities are prepared for at least three surfactant concentrations in screw-cap test tubes. Typically, surfactant concentration will range from 0 to 10 wt%, and salinity will vary according to the reservoir of interest. Sample tubes all contain an identical amount of brine, usually between 50 and 80% by volume. Sample tubes are mixed regularly for several days, then allowed to equilibrate. The equilibration process can take anywhere from several days to several months, depending on emulsion stability. 

Figure 6 shows an idealized salinity requirement diagram. Within the type III phase environment, three phases occur in the area indicated, but two phases occur in the rest of the type III region. Type II(+) phase behavior occurs above the type III region, and the type II(-) behavior occurs below. Midpoint salinity is shown near the middle of the type III region. 

Figure 6, Idealized salinity requirement diagram. (Modified and reproduced with permission from reference 32. Copyright 1982 Society of Petroleum Engineers.)...

From the previous discussion, we can see that which salinity system is favored depends on the salinity requirement diagram, and the diagram depends on the surfactant system. In diagram I, the SG(-) system may be the most... 

Nelson, R.C., 1982. The salinity-requirement diagram—a useful tool in chemical flooding research and development. SPEJ (April), 259-270. 

Finite Chemical Slug—Salinity Requirement Diagrams... 

This is the type of information that is presented in a Salinity Requirement Diagram. Figure 6 is the Salinity Requirement Diagram for the system under discussion. The vertical bars show, as a function of overall surfactant concentration, the range of brine salinity over which the system is in a Type III phase environment (although not necessarily three phases). The position of the circle on the bar indicates midpoint salinity at that overall surfactant concentration. Optimal salinity for oil-displacement efficiency should be close to that level of salinity. The number within the circle is the volume fraction of surfactant in the invariant phase at midpoint salinity. Healy and Reed (12) found lower microemulsion /ex cess brine and microemulsion/excess oil interfacial tensions for systems in which the volume fraction of surfactant in... 

Fig. 6. Salinity Requirement Diagram for 80/20, Petrostep 450/ NEODOL 25-3S, surfactant blend with sodium chloride brines,...

Absolute values of M /Na" effectiveness and the dependency of those values on surfactant concentration depend upon the particular surfactant or surfactant blend. For example, for Petrostep 450 alone in the same system as the 80/20, Petrostep 450/NEODOL 25-3S, blend we have been discussing, the M /Na" effectiveness ratio rises from 21 to 67 as the surfactant concentration is lowered from 5.0 to 2.0 percent. On the ocher hand, judging from how "flat its Salinity Requirement Diagram is, the M /Na+ effectiveness ratio for NEODOL 25-3S by itself does not change much with surfactant concentration. (The midpoint salinity of NEODOL 25-3S drops only 11 percent, from 185 percent to 165 percent SDSW, as its concentration in the subject system is decreased from 5.0 to 0.8 percent.)... 

The "steepness" of a Salinity Requirement Diagram indicates how rapidly the M /Na+ effectiveness ratio changes with surfactant concentration. If that ratio did not change at all with surfactant concentration, Salinity Requirement Diagrams made with multivalent cations in the brine would parallel the "flat" diagrams, such as Figure 6, found when the only cations in the brine are sodium. 

Salinity Requirement Diagrams for Various Organic Sulfonates... 

Considerable differences exist in Salinity Requirement Diagrams of various organic sulfonates. Table 3 shows midpoint salinities and the percent surfactant in the "invariant" microemulsion phase at midpoint salinity for three Stepan petroleum sulfonates. 

Witco s petroleum sulfonate, Petronate TRS 12B, is similar to Petrostep 465, and Witco s Petronate TRS lOB falls between Petro-step 465 and Petrostep 450. The Salinity Requirement Diagram of Amoco s (polybutene) Sulfonate 151 lies even lower than the diagrams for Petrostep 465 and Petronate TRS 12B. Midpoint salinity for that sulfonate at 5.0 percent surfactant in the system is about five percent SDSW. 

Table 3 illustrates how surfactants of quite different midpoint salinities at high surfactant concentration can exhibit similar midpoint salinities at low surfactant concentration. The increase in slope of the Salinity Requirement Diagram in the order Petrostep 465 < Petrostep 450 < Petrostep 420, correlates with decreasing average molecular weight of the petroleum sulfonate however, we believe that the amount of disulfonate in those products increases in that same order. 

Fig. 8. Surfactant concentration versus salinity superimposed upon Salinity Requirement Diagram for 70/20/10, Petrostep 450/ NEODOL 25-3S/isobutyl alcohol, blend.

Superimposed on the Salinity Requirement Diagram of Figure 8 are data relevant to the set of four chemical floods. In each flood the formation brine was 100 percent SDSW no preflood was used. The 12 percent pore volume chemical slug used in each flood was of the composition shown in the figure after, in effect, mixing... 

---