Geoscience Reference

In-Depth Information

1

Endpoint k
ro

Total fluid

mobility

Endpoint k
rw

k
ro

k
rw

0

1

Water Saturation

S
wor

S
wc

S
or
= 1 - S
wor

Also called S
wi

Fig. 4.5
Example oil-water relative permeability functions

Fig. 4.6
Example gas-oil

relative permeability

functions

1

Straight-line

approximation

k
rog

k
rg

0

1

Gas Saturation

S
gc

S
gmax
= 1 - S
or
- S
wi

S
gmax

arise from poor treatment or understanding of

these endpoints.

The most common functions used for relative

permeability are the Corey exponent functions:

Typical values for a water-wet light oil might be:

3

3

k
ro
¼

0

:

85 1

ð

S
wn

Þ

and k
rw
¼

0

:

3S
w
ðÞ

ð

4

:

9

Þ

x

k
ro
¼

A1

ð

S
wn

Þ

ð

4

:

6

Þ

A similar set of functions can be used to

describe a gas-oil system (Fig.
4.6
), where the

functions are bounded by the critical gas satura-

tion, S
gc
, and the maximum gas saturation, S
gmax
.

However, gas-oil relative permeability curves

tend to have less curvature (lower Corey

exponents) and sometimes straight-line functions

y

k
rw
¼

BS
w
ðÞ

ð

4

:

7

Þ

where S
wn
is the normalized saturation:

S
wn
¼

ð

S
w

S
wc

Þ=

ð

S
wor

S
wc

Þ

ð

4

:

8

Þ