Page 264 - Petrophysics 2E

FORMATION RESISTMTY FACTOR 237

TABLE 4.6
SATURATION AND RESISTANCE VALUES FOR CORE SAMPLE

sw r0
(fraction) (ohm)
1 .ooo 52 1
0.900 678
0.800 913
0.730 1,151
0.640 1,510
0.560 2,255
0.480 3,135
0.375 5,270
0.350 6,820
0.300 10,400

EXAMPLE

A sandstone core sample (d = 1.90 cm and L = 3.20 cm) is saturated
with brine of 0.55 ohm-m resistivity. The core was desaturated in steps,
and the resistance (Table 4.6) was measured at each saturation.

(a) Estimate the rock porosity.
(b) Determine the saturation exponent, n, by the conventional
technique .

SOLUTION

(a) The rock porosity may be estimated from Humble equation, 4.3.
The resistivity of the rock sample, 100% water saturated, is obtained
from:

A 2.835 x lo-*
& = To- = 521 = 4.6162 Q-m
L 0.032

The formation resistivity factor is (Equation 4.5):

& 4.6162
F=-= -- - 8.393
R, 0.55