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Chapter 8 Induction logs
Lecture notes for PET 370
Spring 2012
Prepared by: Thomas W. Engler, Ph.D., P.E.
Why resistivity logs?
Estimate Rt
Why need Rt?
Resistivity Logs Introduction
tR
wFR
wS
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
Rmf<2Rw
Or
Rt>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
Rmf>2Rw
Or
Rt<200
obsoleteES, ELup to
1955
18’ Lateral64” Normal16” Normal
CommentsNameYearsDeep
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
Rmf<2Rw
Or
Rt>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
Rmf>2Rw
Or
Rt<200
obsoleteES, ELup to
1955
18’ Lateral64” Normal16” Normal
CommentsNameYearsDeep
3+ ft
Medium
1.5-3 ft
Shallow
0.5-1.5 ft
Flushed
Zone
1-6 in.
Resistivity Logs Classification
Resistivity Logs Example: Old ES
19’ Lateral
10” Normal
32” LS Lateral
Bagley Penn Field
Chambers No. 2
Lea County, NM
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
Rmf<2Rw
Or
Rt>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
Rmf>2Rw
Or
Rt<200
obsoleteES, ELup to
1955
18’ Lateral64” Normal16” Normal
CommentsNameYearsDeep
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
Rmf<2Rw
Or
Rt>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
Rmf>2Rw
Or
Rt<200
obsoleteES, ELup to
1955
18’ Lateral64” Normal16” Normal
CommentsNameYearsDeep
3+ ft
Medium
1.5-3 ft
Shallow
0.5-1.5 ft
Flushed
Zone
1-6 in.
Resistivity Logs Classification
Resistivity Logs Example: IEL
IES or IEL; short normal or
spherically focused curve
with a deep induction.
(No correction for invasion!)
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
Rmf<2Rw
Or
Rt>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
Rmf>2Rw
Or
Rt<200
obsoleteES, ELup to
1955
18’ Lateral64” Normal16” Normal
CommentsNameYearsDeep
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
Rmf<2Rw
Or
Rt>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
Rmf>2Rw
Or
Rt<200
obsoleteES, ELup to
1955
18’ Lateral64” Normal16” Normal
CommentsNameYearsDeep
3+ ft
Medium
1.5-3 ft
Shallow
0.5-1.5 ft
Flushed
Zone
1-6 in.
Resistivity Logs Classification
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 spherically
focused shallow log; DISF
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
Rmf<2Rw
Or
Rt>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
Rmf>2Rw
Or
Rt<200
obsoleteES, ELup to
1955
18’ Lateral64” Normal16” Normal
CommentsNameYearsDeep
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
Rmf<2Rw
Or
Rt>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
Rmf>2Rw
Or
Rt<200
obsoleteES, ELup to
1955
18’ Lateral64” Normal16” Normal
CommentsNameYearsDeep
3+ ft
Medium
1.5-3 ft
Shallow
0.5-1.5 ft
Flushed
Zone
1-6 in.
Resistivity Logs Classification
Resistivity Logs Example: High resolution or Phasor induction
Conventional
induction log
Phasor
induction log
Source: Halliburton
Next improvement is known
as the Phasor Induction
Tool - better thin bed
resolution and automatic
corrections
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
Rmf<2Rw
Or
Rt>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
Rmf>2Rw
Or
Rt<200
obsoleteES, ELup to
1955
18’ Lateral64” Normal16” Normal
CommentsNameYearsDeep
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
Rmf<2Rw
Or
Rt>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
Rmf>2Rw
Or
Rt<200
obsoleteES, ELup to
1955
18’ Lateral64” Normal16” Normal
CommentsNameYearsDeep
3+ ft
Medium
1.5-3 ft
Shallow
0.5-1.5 ft
Flushed
Zone
1-6 in.
Resistivity Logs Classification
Resistivity Logs Example: Array induction
AIT log
DIL log
Ambiguous
reading
Correct
reading
Source: Halliburton
90
10
Resistivity Logs
• where fresh mud or oil-base mud (or air-filled holes) is used,
• where the Rmf/Rw ratio is greater than 2.5 to 3,
• where Rt is less than 200 ohm-m
Selection – Induction log
Resistivity Logs Theory
Circumferential Current I
Mud
Invaded zone
Tool Rm Rxo Rt
Uninvaded zone
it
Gm/Rm
Gxo/Rxo
Gt/Rt
Induction Equivalent Circuit
Im
Ixo
IT
sCsGtCtGxoCxoGmCmGILDC
or
sR
sG
tR
tG
xoR
xoG
mRmG
ILDR
1
Read apparent resistivity from well log,Ra
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
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
Resistivity Logs
Given 1.5” standoff in a 14.6” hole Rm = 0.35 ohm-m ILD = 50 ohm-m (20
mmho/m) Solution hole signal = 5.7 mmho/m Ct (corr) = Ct - hole signal Rt = 70 ohm-m
Borehole Correction
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
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
sC
sG
tC
tG
xoC
xoG
mC
mG
ILDC
sC
sG
tC
tG
xoC
xoG
mC
mG
ILDC
ILDC
tC
tG
xoC
xoG
sC
sG
ILDC
ILDC
Resistivity Logs
• The bed thickness effect is a f(bed thickness, vertical resolution of tool, resistivity contrast Rt/Rs)
• Corrections necessary for:
– thick beds w/ Rt/Rs >> 1 – thin beds with large Rt/Rs contrast
Bed thickness correction
Resistivity Logs Bed thickness correction
Deep Induction Log Bed Thickness
Correction (Schlumberger)
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
sC
sG
tC
tG
xoC
xoG
mC
mG
ILDC
sC
sG
tC
tG
xoC
xoG
mC
mG
ILDC
ILDC
tC
tG
xoC
xoG
sC
sG
ILDC
ILDC
SFLC
ILMC
tC
)i
d(tG
xoC
)i
d(xoG
ILDC
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
Resistivity Logs
Example 1
Given
Rt = 10 ohm-m
Salt mud, Rm = 0.05
Rxo = 1
di = 65”
Solution
G(ILD) = 0.2
Ra = 3.6 ohm-m
(Big error)
Geometric Factors
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
Resistivity Logs
Example
RILD = 10 Wm
RILM = 14 Wm
RSFL = 90 Wm
Invasion Correction
4.1
IDR
IMR
9
IDR
SFLR
(1).
:Solution
Resistivity Logs
Invasion Correction
chart from 89.0
IDR
tR
(2).
m9.8
IDR*
IDR
tR
tR (3).
W
m125xo
R
14
tR
xoR
(4).
W
"50i
d (5).
Resistivity Logs
Invasion Correction
Example
RILD = 10 Wm
RILM = 14 Wm
RSFL = 90 Wm
Resistivity Logs
Example: SFL-ILM-ILD
Big Lake (San Andres)
Resistivity Logs
Invasion Correction
1
2
3
Big Lake (San Andres)
Big Lake (San Andres) Example
Zone ILD ILM SFL SFL/ILD ILM/ILD Rt/RILD Rt Rxo/Rt Rxo di”
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
Resistivity Logs Example: High resolution or Phasor induction
Conventional
induction log
Phasor
induction log
Improvements (1). Thinner bed resolution (2 ft.) (2). Comprehensive set of
automatic corrections for: - shoulder effect and thin bed resolution - skin effect - borehole and cave effect - large boreholes - invasion effects
Resistivity Logs
Array Induction Image Tool (AIT) or High Resolution Imager (HRI) Main features:
1. full borehole corrections over a range of Rt/Rm contrasts
2. the ability to use short array information to solve for effective borehole parameters
3. Five log curves are presented at median depths of investigation of 10, 20, 30, 60 and 90 inches. Three vertical resolutions of 1, 2 and 4 ft.
4. improvement in invasion profiles for both oil- and water-based muds. This includes accurate Rt estimate and a quantitative description of the transition zone.
5. Capability of producing resistivity and saturation images of the formation.
Array Induction
Resistivity Logs Example: Array induction
AIT log
DIL log
Ambiguous
reading
Correct
reading
Source: Halliburton
90
10
Resistivity Logs Example: Array induction
Estimated invaded volumes from AIT log (Halliburton)
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