Rapid Sequence Induction Versus Traditional Induction: An ...
Fmev Chap8a Induction Short Version
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Transcript of Fmev Chap8a Induction Short Version
![Page 1: Fmev Chap8a Induction Short Version](https://reader034.fdocuments.net/reader034/viewer/2022051208/544a9d09af79596c4d8b4963/html5/thumbnails/1.jpg)
Chapter 8 Induction logs
Lecture notes for PET 370
Spring 2011
Prepared by: Thomas W. Engler, Ph.D., P.E.
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• Why resistivity logs?
Estimate Rt
• Invasion
• Resolution (vertical, horizontal)
• Classification
- based on depth of investigation
- salt vs fresh mud
Resistivity Logs Introduction
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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
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
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Resistivity Logs
• IES or IEL; short normal or spherically focused curve with a deep induction. (No correction for invasion!)
• 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 • Next improvement is known as the Phasor Induction Tool - better thin bed
resolution and automatic corrections • Latest generation induction tool known as Array Induction Tool or Imager -
eliminates need for assumption of a step function for the invasion profile.
Induction Log History
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Resistivity Logs Example: Old ES
19’ Lateral
10” Normal
32” LS Lateral
Bagley Penn Field
Chambers No. 2
Lea County, NM
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Resistivity Logs Example: IEL
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Resistivity Logs Example: High resolution or Phasor induction
Conventional
induction log
Phasor
induction log
Source: Halliburton
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Resistivity Logs Example: Array induction
AIT log
DIL log
Ambiguous
reading
Correct
reading
Source: Halliburton
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Resistivity Logs
• where fresh mud or oil-base mud (or air-filled holes) is used,
• where the Rmf/Rw ratio is greater than 3,
• where Rt is less than 200 ohm-m, and
Selection – Induction log
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Resistivity Logs
• measures conductivity C= 1000/R (mmho/m)
• current is fed to a transmitter which generates a magnetic field and hence a circular current in the media.
• This current induces a voltage at the receiver .
• Array of transmitter-receiver coils; jamming the signal into the desired formation. Thus, minimizes borehole, invasion, and adjacent bed effects.
• Typically, six or more coil pairs, 40” spacing from main coil to obtain deep reading.
• Only resistivity tool to run in air drilled holes.
Principle of Operation
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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
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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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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
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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
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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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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
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Resistivity Logs Bed thickness correction
Deep Induction Log Bed Thickness
Correction (Schlumberger)
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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
Example
RILD = 10 Wm
RILM = 14 Wm
RSFL = 90 Wm
Invasion Correction
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Resistivity Logs
Invasion Correction
Example
RILD = 10 Wm
RILM = 14 Wm
RSFL = 90 Wm
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Resistivity Logs Invasion Correction
"50id (5).
m144xoR16tR
xoR (4).
m9.8IDR*IDR
tRtR (3).
chart from 89.0IDR
tR (2).
4.1IDR
IMR;9
IDR
SFLR (1).
:Solution
m- 90 14, 10, are
readings shallow and medium, Deep, :Given
W
W
W
sCorrection Invasion of Example
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Resistivity Logs
Example: SFL-ILM-ILD
Big Lake (San Andres)
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Resistivity Logs
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
Phasor Induction
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Resistivity Logs Example: High resolution or Phasor induction
Conventional
induction log
Phasor
induction log
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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
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Resistivity Logs Example: Array induction
AIT log
DIL log
Ambiguous
reading
Correct
reading
Source: Halliburton
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Resistivity Logs Example: Array induction
Estimated invaded volumes from AIT log (Halliburton)
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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