2. Outline
• Definitions and Uses
• Resistivity in Rocks
• Archie’s Equations
• Invasion and Invasion Models
• Measuring Resistivity (Rt and Rxo)
• Basic ES Principles
• Focused Devices
• Micro Resistivity Devices
3. Resistivity Uses
• Locate Hydrocarbons
• Identify Water Type
• Correlation
• Identify Lithology of Formations
4. Resistivity
• The opposition to flow of electrical current
offered by a material of unit length and unit
cross sectional area.
V
A
L
r
5. Measuring Resistivity
V - Voltage in Volts R - Resistance in Ohms
I - Current in Amperes A - Area in Square Meters
L - Length in Meters
R
V
A
L
r
V = R x I
V = I R
V = r L / A I
r = V / I k
R = r L / A
r = V/ I A / L
( k = A / L )
18. Resistivity Factors
• The Formation Resistivity is effected by:
• Volume of Water - (Porosity & Sw)
• Resistivity of Water - (Rw)
• Current path through Water - “m” in Porosity
equation
19. Resistivity
Which of these “Archie Blocks” has the largest resistivity
Rt = Ro
Rt = Ro Rt > Ro
= 20%
Sw = 100%
BVW = .02
= 30%
Sw = 66%
BVW = .0199
= 10%
Sw = 100%
BVW = .01
> =
28. Transition Zone - Oil
Resistivity
Depth of Investigation
10 60 90
Virgin
Flushed
29. Transition Zone - Water
Resistivity
Depth of Investigation
10 60 90
Virgin
Flushed
30. Transition Zone - Oil
Annulus Profile,
Deep Invasion,
Oil
Resistivity
Depth of Investigation
10 60 90
Virgin
Ann.
Flushed
31. Basic Log Example
GR
0 150
1
1000
1
1
1
00
SFL
.2 20
ILM
.2 20
DPHI 0
.50
NPHI
.50 0
A
B
C
D
.30
BHT = 230 F
TD = 14000 ft.
Rmf = 1
.41 ohm-m @ 75 F
ILD
.2 20
S P
34. Dual Laterolog
LLS
Ao Measure Current Electrode
M1 & M2 Monitoring Electrodes
A1 Bucking Current Emitting Electrode
A2 Bucking Current Return Electrode
LLD
Ao Measure Current Electrode
M1 & M2 Monitoring Electrodes
A1 Bucking Current Electrode
A2 Bucking Current Electrode
35. Spherical Focused Log
Rsfl =
k (Vb - Vc)
Io
Io Return
to Armor
Bucking Current
Monitoring Electrodes
Buckimg Current
Return Electrode
Monitoring Electrode
Current Electrode
36. Proximity Log - Microlog
Ao Mo A1
M2
M1
Ao
Ao
Mo
A1
M1
M2
M2
M1
Ao
Microlog
Microlog
Editor's Notes
#31:An example of a basic Triple Combo Log showing SP, GR, Resistivity, neutron-porosity and density-porosity readings.
Other curves that would normally be presented are: Cable Tension, Head Tension, Hole Caliper, Computed Data.
Is there any Hydrocarbons in this well???
#32:The basic electrical measurements were made with electrodes placed on a “bridle”.
With a constant current flow, the voltage of equal-potential spheres which occurs at electrodes could be measured. This is used to calculate resistivity.
Various electrode patterns were used to give readings at different depths into the rocks.
Since this was an un-focused arrangement, the “k” constant is theoretically calculated based on an iso-tropic, homogeneous medium. In practice, “k” was a variable based on the resistivities encountered.
#33:Non-focused electrical systems do not work good in wells drilled in high resistivity formations with salty muds. The current paths will concentrate in the mud column and surrounding low resistivity formations, resulting in low and incorrect values for Rt in the zone of interest.
Focused devices have voltage controlled focusing electrodes to force the measure currents into a finite path deeper into the formations, resulting in a better Rt determination.
#34:Used as the primary logging tool when the Rt/Rm ratio is high.
This occurs in wells drilled with Salt muds and formations of high resistivity (greater than 50-100 ohms meters).
Two electrode arrangements are used to get readings from different depths of investigation.
#35:This device is the currently accepted focused electrical measurement in wells drilled with fresh muds.
It does a good job of reading Rxo if the bed thickness is greater than 18 inches and the invasion diameter is greater than 30 inches.
#36:The MSFL is designed to read the flushed zone resistivity and will help in defining thin permeable beds that are drilled with all types of water-based mud (fresh or salty).
The Microlog is an older un-focused device that works well in zones drilled with fresh muds. It is also used for thin, permeable bed definition.
#37:Depth of Investigation for logging tools are defined as the distance that gives a geometric factor of .5
This means that one-half of the signal is being received from the region between the borehole wall and that depth.
Example: The MSFL is receiving 50% of it’s signal from a region within 10 inches of the borehole wall.
#38:The MSFL is designed to read the flushed zone resistivity and will help in defining thin permeable beds that are drilled with all types of water-based mud (fresh or salty).
The Microlog is an older un-focused device that works well in zones drilled with fresh muds. It is also used for thin, permeable bed definition.
