Electrical Properties

1
Electrical Properties Archies Law
2
Rock containing pores saturated with water and
hydrocarbons
Non-shaly rock, 100 saturated with water having
resistivity, Rw
Rt
Cube of water having resistivity, Rw

• 20
• Sw 20

Ro

• 20
• Sw 100

Rw

• 100
• Sw 100

Saturation Equation
Resistivity
Formation Factor Equation
3
Formation Factor

• The formation factor (F) depends on
• Porosity of the formation,
• Pore geometry - tortuosity
• Lithology of the formation
• Degree of cementation, and
• Type and amount of clay in the rock

From J. Jensen, PETE 321 Lecture Notes
4
Formation Factor Equation

• Archies equation for formation factor is a power
  law model
• FR0/Rwaf-m

1000
Rock type 1
100
10
Rock type 2
1
Note Sw1
.01
.1
1.0
From NExT, 1999
5
Formation Factor - Example Core Data
a ? 1.0
From J. Jensen, PETE 321 Lecture Notes
6
Formation Factor

• Faf-m
• a constant ? 1.0 for most formations
• m cementation factor ? 2 for most formations
• Other commonly used values
• Sandstones
• F 0.8/f2 (Tixier)
• 0.62/f2.15 (Humble)
• Carbonates
• F 0.8/f2

From J. Jensen, PETE 321 Lecture Notes
7
Saturation Equation

• Power Law Model
• IRRt/R0Sw-n
• Each curve for a specific core sample
• No conductive materials (clay) present

From NExT, 1999
8
Laboratory Determination of Saturation Exponent, n
From J. Jensen, PETE 321 Lecture Notes
9
R0 Appears in Both Equations
From NExT, 1999
10
Archies Equation (Combined)
From NExT, 1999
11
IDEALIZED LOG SET
From J. Jensen, PETE 321 Lecture Notes
12
Effect of Filtrate Invasion -Rnear_well ? Rt
(permeability present)
Modified from J. Jensen, PETE 321 Lecture Notes
13
EXAMPLE LOG WITH RESISTIVITY
From NExT, 1999
14
Laboratory Resistance
From J. Jensen, PETE 321 Lecture Notes
15
Laboratory Resistivity

• Resistivity

From J. Jensen, PETE 321 Lecture Notes