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Transcript of Chap8a Induction Lecturenotes
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Chapter 8
Induction logs
Lecture notes for PET 370
Spring 2012
Prepared by: Thomas W. Engler, Ph.D., P.E.
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Why resistivity logs?
Estimate Rt
Why need Rt?
Resistivity Logs Introduction
tR
wFR
wS
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Obsolete
current
LL7, LL3,
guard
DLL-MLL
DLL-
MSFL
1955-80
1972
Deep
Laterolog
(LLD)
Laterolog-7
Laterolog-3 /
Guard
Shallow
Laterolog
(LLS)
Micro-
laterolog
(MLL)
MLL
MSFL
Salt
Mud
R mf
<2R w
Or
R t>200
CurrentAIT1990ToolInductionArray
Obsolete
Obsolete
Obsolete
Current
Current
IES, IEL
ISF
DIL-LL8,
DIFL,DISG
DIL-SFL
Phasor
1955-80
1970-85
1965
1975
1985
Induction
(6FF40)
Deep
Induction
Deep
Phasor
Induction
Medium
Induction
Medium
Phasor
Induction
16”Normal
Spherically
Focused
LL8/Short
Guard
Spherically
Focused
Spherically
Focused
Microlog
(ML)
Minilog
Proximity
(PL)
Fresh
Mud
R mf
>2R w
Or
R t<200
obsoleteES, ELup to
1955
18’ Lateral64” Normal16” Normal
Comments NameYearsDeep
3+ ft
Medium
1.5-3 ft
Shallow
0.5-1.5 ft
Flushed
Zone
1-6 in.
Obsolete
current
LL7, LL3,
guard
DLL-MLL
DLL-
MSFL
1955-80
1972
Deep
Laterolog
(LLD)
Laterolog-7
Laterolog-3 /
Guard
Shallow
Laterolog
(LLS)
Micro-
laterolog
(MLL)
MLL
MSFL
Salt
Mud
R mf
<2R w
Or
R t>200
CurrentAIT1990ToolInductionArray
Obsolete
Obsolete
Obsolete
Current
Current
IES, IEL
ISF
DIL-LL8,
DIFL,DISG
DIL-SFL
Phasor
1955-80
1970-85
1965
1975
1985
Induction
(6FF40)
Deep
Induction
Deep
Phasor
Induction
Medium
Induction
Medium
Phasor
Induction
16”Normal
Spherically
Focused
LL8/Short
Guard
Spherically
Focused
Spherically
Focused
Microlog
(ML)
Minilog
Proximity
(PL)
Fresh
Mud
R mf
>2R w
Or
R t<200
obsoleteES, ELup to
1955
18’ Lateral64” Normal16” Normal
Comments NameYearsDeep
3+ ft
Medium
1.5-3 ft
Shallow
0.5-1.5 ft
Flushed
Zone
1-6 in.
Resistivity Logs Classification
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Obsolete
current
LL7, LL3,
guard
DLL-MLL
DLL-
MSFL
1955-80
1972
Deep
Laterolog
(LLD)
Laterolog-7
Laterolog-3 /
Guard
Shallow
Laterolog
(LLS)
Micro-
laterolog
(MLL)
MLL
MSFL
Salt
Mud
R mf
<2R w
Or
R t>200
CurrentAIT1990ToolInductionArray
Obsolete
Obsolete
Obsolete
Current
Current
IES, IEL
ISF
DIL-LL8,
DIFL,DISG
DIL-SFL
Phasor
1955-80
1970-85
1965
1975
1985
Induction
(6FF40)
Deep
Induction
Deep
Phasor
Induction
Medium
Induction
Medium
Phasor
Induction
16”Normal
Spherically
Focused
LL8/Short
Guard
Spherically
Focused
Spherically
Focused
Microlog
(ML)
Minilog
Proximity
(PL)
Fresh
Mud
R mf
>2R w
Or
R t<200
obsoleteES, ELup to
1955
18’ Lateral64” Normal16” Normal
Comments NameYearsDeep
3+ ft
Medium
1.5-3 ft
Shallow
0.5-1.5 ft
Flushed
Zone
1-6 in.
Obsolete
current
LL7, LL3,
guard
DLL-MLL
DLL-
MSFL
1955-80
1972
Deep
Laterolog
(LLD)
Laterolog-7
Laterolog-3 /
Guard
Shallow
Laterolog
(LLS)
Micro-
laterolog
(MLL)
MLL
MSFL
Salt
Mud
R mf
<2R w
Or
R t>200
CurrentAIT1990ToolInductionArray
Obsolete
Obsolete
Obsolete
Current
Current
IES, IEL
ISF
DIL-LL8,
DIFL,DISG
DIL-SFL
Phasor
1955-80
1970-85
1965
1975
1985
Induction
(6FF40)
Deep
Induction
Deep
Phasor
Induction
Medium
Induction
Medium
Phasor
Induction
16”Normal
Spherically
Focused
LL8/Short
Guard
Spherically
Focused
Spherically
Focused
Microlog
(ML)
Minilog
Proximity
(PL)
Fresh
Mud
R mf
>2R w
Or
R t<200
obsoleteES, ELup to
1955
18’ Lateral64” Normal16” Normal
Comments NameYearsDeep
3+ ft
Medium
1.5-3 ft
Shallow
0.5-1.5 ft
Flushed
Zone
1-6 in.
Resistivity Logs Classification
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Resistivity Logs
Example: IEL
IES or IEL; short normal or
spherically focused curve
with a deep induction.
(No correction for invasion!)
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Obsolete
current
LL7, LL3,
guard
DLL-MLL
DLL-
MSFL
1955-80
1972
Deep
Laterolog
(LLD)
Laterolog-7
Laterolog-3 /
Guard
Shallow
Laterolog
(LLS)
Micro-
laterolog
(MLL)
MLL
MSFL
Salt
Mud
R mf
<2R w
Or
R t>200
CurrentAIT1990ToolInductionArray
Obsolete
Obsolete
Obsolete
Current
Current
IES, IEL
ISF
DIL-LL8,
DIFL,DISG
DIL-SFL
Phasor
1955-80
1970-85
1965
1975
1985
Induction
(6FF40)
Deep
Induction
Deep
Phasor
Induction
Medium
Induction
Medium
Phasor
Induction
16”Normal
Spherically
Focused
LL8/Short
Guard
Spherically
Focused
Spherically
Focused
Microlog
(ML)
Minilog
Proximity
(PL)
Fresh
Mud
R mf
>2R w
Or
R t<200
obsoleteES, ELup to
1955
18’ Lateral64” Normal16” Normal
Comments NameYearsDeep
3+ ft
Medium
1.5-3 ft
Shallow
0.5-1.5 ft
Flushed
Zone
1-6 in.
Obsolete
current
LL7, LL3,
guard
DLL-MLL
DLL-
MSFL
1955-80
1972
Deep
Laterolog
(LLD)
Laterolog-7
Laterolog-3 /
Guard
Shallow
Laterolog
(LLS)
Micro-
laterolog
(MLL)
MLL
MSFL
Salt
Mud
R mf
<2R w
Or
R t>200
CurrentAIT1990ToolInductionArray
Obsolete
Obsolete
Obsolete
Current
Current
IES, IEL
ISF
DIL-LL8,
DIFL,DISG
DIL-SFL
Phasor
1955-80
1970-85
1965
1975
1985
Induction
(6FF40)
Deep
Induction
Deep
Phasor
Induction
Medium
Induction
Medium
Phasor
Induction
16”Normal
Spherically
Focused
LL8/Short
Guard
Spherically
Focused
Spherically
Focused
Microlog
(ML)
Minilog
Proximity
(PL)
Fresh
Mud
R mf
>2R w
Or
R t<200
obsoleteES, ELup to
1955
18’ Lateral64” Normal16” Normal
Comments NameYearsDeep
3+ ft
Medium
1.5-3 ft
Shallow
0.5-1.5 ft
Flushed
Zone
1-6 in.
Resistivity Logs Classification
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Resistivity Logs
Example:
SFL-ILM-ILD
Big Lake (San Andres)
Replaced in the mid-
1960s with a Dual
induction tool (shallow,medium, and deep
curves); DIL-LL8, DIFL,
DISG
Improved DIL with the
addition of the sphericallyfocused shallow log; DISF
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Resistivity Logs
Example: High resolution
or Phasor induction
Conventional
induction log
Phasor
induction log
Source: Halliburton
Next improvement is known
as the Phasor InductionTool - better thin bed
resolution and automatic
corrections
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Resistivity Logs Example: Array induction
AIT log
DIL log
Ambiguous
reading
Correct
reading
Source: Halliburton
90
10
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Resistivity Logs
• where fresh mud or oil-base
mud (or air-filled holes) is
used,
• where the Rmf /Rw ratio isgreater than 2.5 to 3,
• where Rt is less than 200
ohm-m
Selection – Induction log
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Resistivity Logs Theory
Circumferential Current I
Mud
Invaded zone
Tool R m R xo R t
Uninvaded zone
it
Gm/R m
Gxo/R xo
Gt/R t
Induction Equivalent Circuit
Im
Ixo
IT
sCsGtCtGxoCxoGmCmGILDC
or sR
sG
tR
tG
xoR
xoG
mR
mG
ILDR
1
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Read apparent resistivity from well log,RILD or CILD
Correct for borehole effect (if necessary)
Resistivity Logs Determination of Rt
sC
sG
tC
tG
xoC
xoG
mC
mG
ILDC
sC
sG
tC
tG
xoC
xoG
mC
mG
ILDC
ILDC
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Resistivity Logs
Given 1.5” standoff in a 14.6” hole
Rm = 0.35 ohm-m
ILD = 50 ohm-m (20mmho/m)
Solution
hole signal = 5.7 mmho/m
Ct (corr) = Ct - hole signal
Rt = 70 ohm-m
Borehole Correction
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Resistivity Logs
• significant when:
- mud is salty
- hole size is large and/or oval
- formation resistivity is high
• Corrections greatest for:
- induction tool against borehole, standoff is zero.- ILM than ILD
- holes > 12”
Borehole Correction
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Read apparent resistivity from well log,RILD or CILD
Correct for borehole effect (if necessary)
Correct for bed thickness effect (if necessary)
Resistivity Logs Determination of Rt
sCsGtCtGxoCxoGmCmGILDC
sC
sG
tC
tG
xoC
xoG
mC
mG
ILDC
ILDC
tC
tG
xoC
xoG
sC
sG
ILDC
ILDC
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Resistivity Logs
Bed thickness correction
Deep Induction Log Bed Thickness
Correction
(Schlumberger)
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Read apparent resistivity from well log,RILD or CILD
Correct for borehole effect (if necessary)
Correct for bed thickness effect (if necessary)
Correct for invasion effect (if three curves are present)
True formation resistivity, Rt
Resistivity Logs Determination of Rt
sCsGtCtGxoCxoGmCmGILDC
sC
sG
tC
tG
xoC
xoG
mC
mG
ILDC
ILDC
tC
tG
xoC
xoG
sC
sG
ILDC
ILDC
SFLC
ILMC
tC
)id(tG
xoC
)id(xoG
ILDC
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Resistivity Logs
Example 1
Given
Rt = 10 ohm-m
Fresh mud, Rm = 1
Rxo = 20
di = 65”
Solution
G(ILD) = 0.2
Ra = 11 ohm-m
(10% error)
Geometric Factors
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Resistivity Logs
Assume a step profile for invasion
Tornado charts to correct for invasion, determine Rt, Rxo, and di
•Rt correction factor between 0.75 and 1.0
• Depth of invasion is reflected by induction resistivity contrast:- Rim/Rid > 1.5 indicates deep invasion
- Rim/Rid < 1.2 indicates shallow invasion
Invasion Correction
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Resistivity Logs
Invasion Correction
Example
RILD = 10 Wm
RILM = 14W
mRSFL = 90 Wm
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Resistivity Logs
Example:
SFL-ILM-ILD
Big Lake (San Andres)
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Resistivity Logs
Invasion Correction
1
2
3
Big Lake (San Andres)
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Big Lake (San Andres) Example
Zone ILD ILM SFL SFL/ILD ILM/ILD Rt/RILD Rt Rxo/Rt Rxodi”
1 10 14 100 10.0 1.40 0.92 9.2 15 138 45
2 44 66 110 2.50 1.50 0.75 33 5 165 90+
3 6.8 8.3 50 7.35 1.22 0.99 6.7 12 80 35
Schlumberger Chart, Rxo/Rm = 20
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Resistivity Logs Example: Array induction
AIT log
DIL log
Ambiguous
reading
Correct
reading
Source: Halliburton
90
10
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Bassiouni, Z: Theory, Measurement, and Interpretation of Well Logs, SPE Textbook
Series, Vol. 4, (1994)
Chapter 5, Sec 5 and 6
Schlumberger, Log Interpretation Charts, Houston, TX (1995)
Western Atlas, Log Interpretation Charts, Houston, TX (1992)
Resistivity Logs References