Page 254 - Petrophysics 2E
P. 254
FORMATION RESISTlvITy FACTOR 227
DO
Figure 4.16. Graphical comparison of Humble equation (‘A), Rosales equation (‘B],
and Timur equation (C) [PJ.
Combining Equations 4.41,4.43, and 4.51 gives:
4tr
Z=l+- (4.52)
@ch
This expression indicates the physical significance of tortuosity in terms
of stagnant and flowing porosities. Equation 4.52 is an approximation
valid only for consolidated porous rocks. For unconsolidated sands, the
general expression (Equation 4.50) should be used, where fG = 1.49 and
m = 1.09.
EXAMPLE
Laboratory measurements made on a Berea Sandstone core yielded
Q = 0.216 and FR = 13.7. Compute:
(a) formation resistivity factor using Rosales, Humble, and Archie
expressions: and compare with the measured value;
(b) the flowing and stagnant porosity; and
(c) tortuosity of the Berea core.
