8/12/2019 2.3 Permeability

1/17

PERMEABILITY

Rock property

independent of fluid flowing through the rock

Absolute permeability k

rock is 100% saturated with the fluid

8/12/2019 2.3 Permeability

2/17

PERMEABILITY

Effective permeability

fluid flowing in the presence of another stationary or

flowing fluid

each fluid has its own effective permeability, kw, ko

dependent on the saturation of each fluid

sum of effective permeability is always less than theabsolute permeability

8/12/2019 2.3 Permeability

3/17

PERMEABILITY

effective permeability

Relative permeability =

absolute permeability

kro= ko/ k

krw= kw/ k

8/12/2019 2.3 Permeability

4/17

PERMEABILITY

End-point relative permeability

maximum relative permeability that occurs

naturally

kro= kro atSwi krw= krw at1 - Sor

Several equations for calculating kroand krwhavebeen published

8/12/2019 2.3 Permeability

5/17

k

kw

0

Sw1 - SorSwc 1

ko

k

00

absolute

permeability

Effective Permeability

8/12/2019 2.3 Permeability

6/17

1

krw

0

Sw1 - SorSwc 1

kro

1

00

kro

krw

Relative Permeability

8/12/2019 2.3 Permeability

7/17

8/12/2019 2.3 Permeability

8/17

=

Effective

permeability to

water behind

the flood front

Effective

permeability to

water at the residual

oil saturation

EFFECTIVE PERMEABILITY

kw@ Sw = kw@ 1-Sor

8/12/2019 2.3 Permeability

9/17

FLUIDMOBILITY

The mobility of any fluid is equal to the ratio

of its effective permeability and viscosity

ko

o=

=

k kro

o

8/12/2019 2.3 Permeability

10/17

8/12/2019 2.3 Permeability

11/17

Mobility of oilahead of the front

ko

o=

ko@ Swc

o

8/12/2019 2.3 Permeability

12/17

Mobility of driving phase

Mobility of displacing phase

Mobility of displaced phase

Mobility behind the front

Mobility ahead of the front=

MOBILITY RATIO

MMobility of driven phase

=

=

8/12/2019 2.3 Permeability

13/17

M =krw/w

kro/o

MOBILITY RATIO

For water flood

Mis known as the end point mobility ratio

kro and krware the end point relative permeabilities

M = constant

8/12/2019 2.3 Permeability

14/17

M = 1

the mobility ahead of and behind

the flood front are equal

the water displaces the oil rather efficiently

the front tends to advance fairly uniformly

effective sweep of the oil from most of

the volume of the reservoir under flood.

8/12/2019 2.3 Permeability

15/17

M > 1

unfavorable mobility ratio

mobility behind the front > the mobility ahead of it

water displaces the oil less efficiently

advance of the front is much less uniform

because of fingering and instabilities

less of the reservoir volume under flood

is swept by the advancing front.

8/12/2019 2.3 Permeability

16/17

M < 1

favorable mobility ratio

mobility behind the front is < the mobility ahead of it

water displaces the oil very efficiently

advance of the flood front is uniform

more of the reservoir volume under flood is

swept by the advancing flood front than for M=1

8/12/2019 2.3 Permeability

17/17