usit client log features interpretation
TRANSCRIPT
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USIT Log features
USIT Microdebonding
What to look forin a USIT log
February-2003
Javier Peyrire
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Table of contentsTable of Contents 2
Common formats 3Cement evaluation examples 5
Good Cement 5
Mud Channel 6
Traces of Cement 7
Cement and Squeeze 8
Light Cement 9
Wet Microannulus 10
USIT Image Interpretation and guide 11
Other Effects (examples) 13
Casing shape and wear 14
Third Interface reflection 18
Centralizers 19
To Remember about USIT 20
Microdebonding 21
Background Information 22
Examples 24
Theory and algorithm 28
Examples of microdebonded logs 31
Limitations and advice 35
To remember about Microdebonding 37
Microdebonding References 38
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USI combined casing +cement presentation
QC Casing Cement
Channel
Bond index
Cement raw
Thickness image
ThicknessInternal radius
Cementinterpreted
Casing cross-section
Amplitude
Processing flags
Eccentering, CCL, gamma Ray
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USI + CBL/VDLcement presentation
QC CBL USI VDL
CBL
VDL
Bond indexAcoustic impedance
Cement image interpreted
CBL, Gamma Ray
Process flags, eccentering
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Good cement
Strongformation
arrival
CBLflat,low
MeanAI 8MRayl
Weakcasingarrival
QC CBL USI VDL
The AI value depends on
the type of cement
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Mud channel andcontaminated cement
Weakformation
arrival
CBLvariable,
high Strongcasing arrival
Channel
Low-Zcement
QC CBL USI VDL
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Partial cementation
Weak formationarrival
CBL flat,high Strong casing
arrival
Traces ofcontaminated
cement
QC CBL USI VDL
Patches of cement within
fluid
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Channel and Squeeze
Channel After squeeze
Perfs
USI
CBL
USI BI VDL USI BI VDL
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Light cement top
Low
impedance
0-4 MRayl
scaleshows
contrast
between
light cementand liquid
Liquid/solid
threshold
set low (2.1)
for light
cement
CBL agreeswith USI
0100
0-4MRayl
Threshold2.1 MRayl
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Wet microannulus
USI is weakly affected
CBL reads near free pipe
Strong, regularcasing arrival
High CBL
Uniformmedium-Z
USI
USI BI VDL
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USI image interpretation
High Z
Patchy
Gas
CementLocalised
MediumLiquid
Micro-debonded
Cement Gas entry ifgas zone
Light orcontam. ExtendedCement
NarrowCementdata
Dry micro-Mud
channelMud
layer +cement
annulus(Debond) Gas
channel
No Squeeze ?Squeeze
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USI CBL/VDL
Resolution 0.6 in to 1.2 in. 360 deg. x 3 ft
Well bonded
cement
Cement Cement
Very light
cement
Low contrast
[special processing
if debonded]
Low contrast from
mud
Dry microann.
Debonded
cement
Dry microann. /gas
(special
processing)
Good/fair bond
Wet microann. Slightly affected Ambiguous
Mud layer Channel Ambiguous
Contaminated
cement
Low-Z cement Ambiguous
Mixed lead/tail
cement
Mixed lead/tail Ambiguous
Mud channel Channel Ambiguous
Gas channel Gas channel Cement/ambiguous
Formation bond Not seen VDL qualitative
Outer casing/
hard formation
Third interface
arrival (not
affected)
Strongly affected
Casing
condition
Very sensitive Slightly sensitive
Mud
attenuation
< 12 dB/cm/MHZ No strict limit
USI and CBL/VDL guide
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Other effects
Casing effects
Third arrival effects (formation)
Centralizers effect
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p rad.
Casing shape effects
Manufacturing patterns often
affect cement image slightly
Does not affect interpretationAm Int Cement
Formation
reflections
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Casing wear can affectcement image
Drill pipe wear creates falsechannel
Falsechannel
Weargroove
QC Casing Cement
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Deformed casing
Deformed casing can cause lostechoes and tool eccentering. Even the
eccentering curve becomes false. The
log must be repeated with a wider
Windowacquisition window.Echoesoutside
acquisitionwindow
Max/min TT TT histogram
Eccentering
Lost echoes
QC Casing Cement
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Narrow
side ofannulus
Channel
Third interface reflections
Galaxypattern
Int.radius
CementThickness
Typical galaxy patterns: interference
between casing resonance and reflections
from outer casing (here) or hard formation.
In this example, it shows good cement except
in free pipe when the casing is close to theformation
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Centralizers and goodcement
USI usually seescentralizers
Important to verifyif casing properlycentralized
Casingjoint
Centralizer
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To remember about USIT
USIT-CBL together: gives ananswer for most of the cases
The casing condition will affectthe log
The cement quality is evaluatedreal time
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USITMicro-debonding
Introduction,
description,advice
?
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Background information
USIT gives a value of the Acoustic
Impedance (AI) of the media behindthe casing
In general:
AI gas < 0.3 MRay
AI liquid < 2.6 Mray (water around1.5M ray)
AI conventional cement > 2.6 MRay
AI light cement, foam cement often< 2.6 MRay
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Presentation
Presence of low impedance (gas orliquid range) spots/areas within the
cement
Multiple reasons (mixed with gas,fluid, temperature effects whenhardening, light cement, foamedcement)
Act as a barrier to ultrasound
Patchy cement aspect, low bondetc
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Example 1: patchycement
Patchy gas/cement indicates
micro-debondedcement (patchy drymicro-annulus)
Raw BI Interp
Patches of Gasand Liquid
Patches of Goodcement
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Example 2: Extended dry
microannulus
Debonded Cement
Debonding can be
extensive with lowimpedancevariability and notassociated with
gas entry
Raw BI Interp
Extended debond(reading gas)
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Example 3: Gas Micrannulus
Gas coming tosurface of old
storage well Old CBL showed
almost 100% bondNarrow gas
channelGas microannulus
Good cement
Raw BI Interp
New USI showedareas of debond(gas microannulus)
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Micro-debond on USI andCBL
CBL less affected than USI withoutpressure
USI and CBL
Without pressure
improve with pressure
With pressure
CBL
USI
USI BI VDL USI BI VDL
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Theory or Hypothesis
Gas and liquids have ahomogeneous AI within the same
medium
Solids have a more heterogeneousAI repartition (Variable cementimpedance is indicative of solids)
Cement is a solid (when hardened)
By comparing the AI ofneighbouring points we candetermine if it is a solid or a fluid
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Micro-debonded cementprocessing
VerticalDeviation
Transducer Diagonal 1spot size
Horizontal
Deviation
Diagonal 2
If all 4 standard deviations > setthresholds
Data point is considered to be
locally debonded
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Micro-debond logic
Micro-debonding
algorithmPixel Z AI Thresholds Cement
Liquid
< Thresh
OR
> Thresh
Micro-D
Gas Thresh
Micro-D
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USI micro-debond logic
Classifies patchy low-impedancematerial as micro-debondedcement
Helps interpretation of light andfoam cement LowCBL
FormationarrivalsMicro-debond
presentationConventional
BI CBL VDLBI Map Map
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Micro-debond logicexample
Automatically classifies patchylow-impedance material asmicro-debonded cement
CBL
BI Map CBL VDL
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Debondlogic
Threshold map
BI VDL
LiteCRETE 12 ppg cement
Gas entry from known gas zone
Micro-debond logic showscement is present
CBTBI
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CBTBI
Raw map Z BI Debond
logic
LiteCRETE Gasblok 10.3ppg
Micro-debond logic shows cementis present
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USI micro-debond logiclimitations
Does not work with extended drydebond (gas microannulus)
Empirical threshold
Need to tune thresholdsometimes
Can indicate debonding in achannel due to casing shapeeffects.
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Logging advice
Normal cement
Log with micro-debonding off
Play-back with micro-debondingon if bad bond.
Light/Foam Cement (low AcousticImpedance)
Log with micro-debonding on
Play-back with micro debondingoff to see the AI map (not hiddenby the green micro-debonding
flag)
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To remember
Act as a barrier to ultrasound
Vocabulary: Microdebond is thesame as dry microannulus, gasmicroannulus or dry debond
Indicates solid cement
Often occur without gas entry evenin double casing strings due topressure or temperature changes
Gas entry should only be suspectedif in known gas zone, gas injectorwell near, or gas at surface
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References
Microdebonding: what is it and does it provide hydraulic
isolation?, Andrew Hayman 29 Nov. 2001
SPE 55649, Assessment of FoamedCement Slurries
Using Conventional Cement Evaluation Logs and
Improved Interpretation Methods from Gary J. Frisch,
William L. Graham and James Griffith (SPE, Halliburton)
SPE 19538, Guidelines for Ultrasonic Cement-Sheath
Evaluation from K. J. Goodwin (SPE, Mobil)
Overcoming Interpretation Problems of Gas-
Contaminated Cement Using Ultrasonic Cement Logs
from R.J. Butsch (SPE, Schlumberger)
The Evaluation of Specialized Cements from R.J. Butsch
et al. (SPE, Schlumberger)