Resistivity interpretation

1
Bulk Volume

• The formation is mainly consists of matrix and pore volume.

• Inside pore volume there is fluid.

• Fluid may be water, hydrocarbon or both.

• Volume of porse filled with water is ᶲSw

• Volume of pore spaces filled with oil is ᶲ(1-Sw)

Archie Equation

• R0 is the resistivity of formation filled with water.

• Rt is the resistivity of formation filled with formation fluid.

• Sw can be found as a ratio between Ro and Rt. Sw=Ro/Rt

• Resistivity measured for formation is affected by F(formation factor) and the resistivity of
the fluid in the pore volume of the formation.

• Ro= F*Rw

• Formation factor is factor that try to compensate for the tortuosity of the formation,
means that explain how easy or how hard the current will flow through the formation.

a Rw
S n
w  m
 Rt
Invasion zone saturation.

• The same equation can be used to calculate the saturation of

the mud filtrate in the invasion zone.

• The resistivity of this zones is the Rxo which can be

n aR mf
measured from the Micro log Sxo  m
• The fluid that dominate this zone is the Rmf so it should  R xo
replace the Rw in the archie equation.

• Other formation factor parameters should be the same

because of the same formation.
Determine Rw and Rmf.

• Rw can be determine from the following:

• 1- Rw maps.

• 2- Oil company( the operator)

• 3- From Sp log

• 4- Rwa method

• 5- Ratio method

• 6- Water sample
Rw from Rwa

• In water zone we assume the Sw is 1. (how do we know?)

• We can rewrite Archie as

2
Rw   R t
Rw from ratio method.

• In well drilled with water based mud and in water zone we have Sw =Sxo=1

• Then we put 2 equation equal to each other then we solve Rw.

Rw Rt

Rmf R xo
 Find Rmf(today lab)

Grains/gal
• The blue line are the lines of fixed 10

at 75ÞF
ppm
8

salinities 6
5
20 0
4 10
• You can convert the resistivity of Rmf from 3 30 0
15

surface temperature to BHT 2

40 0

50 0
20
25
60 0

NaCl Concentration (ppm or grains/gal)

30
• Chose the resistivity of the y and the temp 70 0
80 0

Resistivity of Solution (ž - m)
1 40
0
10 0
at which this resistivity measured which is 0.8
12 0
14 0
0
0
50

0.6

surface.
0 0
0.5 17
0
20 0
10 0
0.4
0
30 0
• The point found will be located on salinity
0.3 15 0
0
40 0
20 0
0.2 0 0

lines
50
00 25 0
0
6 0
70 000 30 0
80
40 0
0 00

• Now you can chose the BHT intersect with 0.1 10 , 0 50 0

2 ,00
1
0.08 ,0 00
14
0 00
the same line you found 0.06
0.05
17 ,
20 ,0 00
10 00
00
30 ,0
0.04 15 00

• Read the resistivity of the new point

00
40 ,0 20 00
0.03 00
50 ,0 0
,0 0 25 00
60
00 30 00
70 ,0 00
0.02 80 ,0
40 00
000
10 0, 50 00
0, 000
, 000 2
1 , 000
30 0 14 0 000
17 0, 0
0.01 ,00
200 000 10 ,0 00
25 0,, 000
2 8 0 15 ,0 00
50 75 10 0 12 5 15 0 20 0 25 0 30 0 35 0 40 0
20 ,0 00
10 20 30 40 50 60 70 80 90 10 0 12 0 14 0 16 0 18 0 20 0

Tem perature (ÞF or ÞC)

Sxo and movable oil

• Before invasion Sw will represent the

connate water that didn’t move when oil
invade the rock.

• 1-Sw is oil saturation

• After invasion the saturation of water in the

flushed zone is Sxo which represent also the
saturation of the mud filtrate.

• 1- Sxo represent residual oil

• You can find movable oil by??

• Think about it