PorositySchlumberger

3-1

Por

Formation Resistivity Factor Versus PorosityPor-1

2.5 5 10 20 50 100 200 500 1000 2000 5000 10,000

2.5 5 10 20 50 100 200 500 1000 2000 5000 10,00050

40

3025

20

15

1098765

4

3

2

1

FR, formation resistivity factor

, po

rosit

y (p.

u.)

1.4

1.6

1.82.0

2.2

2.5

2.8

FR =0.81

2

FR =12

FR =0.622.15

FR =1

mm

Vugs orspherical pores

Fractures

Schlumberger

This chart gives a variety of formation resistivity factor-to-porosity conversions. The proper choice is best determined bylaboratory measurement or experience in the area. In the absenceof this knowledge, recommended relationships are the following:For soft formations (Humble formula):

For hard formations:

with appropriate cementation factor, m.

Example: f = 6% in a carbonate in which a cementation factor,m, of 2 is appropriate

Therefore, from chart,FR = 280

FR m=1

,

F FR R= =0 62 0 81

2 15 2.

,.

.

. or