Maximum desaturation capillary number

To further reduce waterflood residual oil saturation, the capillary number must be higher than the preceding calculated value. In general, the capillary number must be higher than a critical capillary number, (Nc)c, for a residual phase to start to mobilize. Practically, this (Nc)c is much higher than the capillary number at normal waterflooding conditions. Another parameter is maximum desaturation capillary number, (Nc)max, above which the residual saturation would not be further reduced in practical conditions even if the capillary number is increased. Lake (1989) used the term total desaturation capillary number for (Nc)max. In practical conditions, total desaturation (i.e., zero residual saturation) may not occur due to some films or blobs trapped in pores. 

Nc)max mean at critical capillary number and maximum desaturation capillary number (Nc) is capillary number and Tp is the parameter used to fit the laboratory measurements. The definition of capillary number used in the preceding equation must be the same as that used in the simulation model. One example of CDC using Eq. 7.121 is shown by the curves in Figure 7.35, and some of the CDC parameters are presented in Table 7.9. The data points in Figures 7.35 and 7.36 are calculated using Eq. 7.124, to be discussed later. 

Now we have discussed the two important capillary numbers critical and maximum. The general relationship between residual saturation of a nonaque-ous or aqueous phase and a local capillary number is called capillary desaturation curve (CDC). The residual saturations start to decrease at the critical capillary number as the capillary number increases, and cannot be decreased further at the maximum capillary number. As discussed earlier, the range of capillary numbers for residual phases to be mobilized is, for example, 10 to... 

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