Page 178 - Standard Handbook Petroleum Natural Gas Engineering VOLUME2

Formation Evaluation 147

Laterolog-8 Borehole Correction
1 '/2-in. (38-mm) Standoff,Thick Beds
1.5
1.4
9 1.3
a
L . 1.2
11.1
= 1.0
0.9
0.8
5 10 20 50 100 200 500 1000 5000 10,000
RLLdRm

SFL" Borehole Correction
1.5
1.4
6 1.3
q 1.2
0
9 1.1
cc" 1.0
0.9
0.8

Figure 5-80a. Borehole correction charts for the laterolog and spherically
focused logs [199].

If a porosity log is not available, FR can be found using Equation 5-45. R, is
selected in a water-bearing zone from the deepest reading resistivity curve. Care
should be taken to select R, in a bed that is thick, permeable, and clean
(shalefree). The zone should be as close to the zone of interest as possible. R,
can sometimes be selected from below the water/hydrocarbon contact within
the zone of interest. Archie's equation (as described earlier) can then be used
to calculate water saturation:
s, = [y] (5-70)
I/e