Page 242 - Petrophysics 2E

FORMATION RESISTIVITY FACTOR 215

where: Xr = resistivity correlation function.
b 1, . . . , b5 = correlation constants.

Table 4.4 shows values of the correlation constants bl, b2, b3, b4, and
b5 for two ranges of resistivity: 0.94 < Rw25< 796 and 0.09 < Rw25 <
1.03. For these two ranges, the conversion of Rw25 into concentration in
mom is straightforward. First, substitute the resistivity value Rw25 into
Equation 4.20 for the appropriate Rw25 range, and then calculate the
resistivity correlation function X,. Second, substitute this value of Xr and
calculate the corresponding value of Csm (mom).
For the case of low resistivity range, i.e., 0.04 < Rw25 < 0.10, Figure 4.7
or the curve-fit equation that follows can be used to convert directly the

TABLE 4.4
RESISTIVITY CORRELATION CONSTANTS FOR EQUATION 4.20"
Range of Resistivity, ohm-m
Resistivity Correlation
Constants 0.94 to 796 0.09 to 1.03
- 1.030224 - 1.0301 5
1.06627 1.06090
2.41239 x lo-' 5.66201 x lo-'
3.68102 x -6.09085 x lo-'
1.46369 x lo-* 5.33566 x lo-'

is
'No direct conversion to concentration correlation, such as Equation 4.19, possible
in the range 0.04 to 0.10.
10

1
0.01 0.1 1
RWZS
Figure 4.7. Conversion correlation between Rw25 and concentration in ppm for the
range 0.04 < Rw25 < 0.1 and 10 < C,, < 5.35.