Cement Evaluation with the UltraSonic
Imager
Andrew Hayman Dominique Guillot Sean Harrera Bernard Piot Gilles Rouault Bob Butsch Charles Morris Matteo Loizzo
Jan. 2000
2/SRPC/
Cement Evaluation with the UltraSonic
Imager
• Introduction
• Acoustic methods basics
• USI tool basics
• USI QC
• USI and CBL/VDL interpretation
• Integrating logs and cementing data
3/SRPC/
Cement Evaluation with the UltraSonic
Imager
• Introduction
– Cementing Problems
– Evaluation methods
• Acoustic methods basics
• USI tool basics
• USI QC
• USI and CBL/VDL interpretation
• Integrating logs and cementing data
4/SRPC/
Objectives of cementing
• Provide complete isolation of zones (Hydraulic isolation)
• Support the casing and protect it from corrosion
5/SRPC/
The ideal wellbore
Thin, impermeable mud filter cake (not gelled or unconsolidated)
BHST at top ofcement>BHCT at TD
Annular gapMinimum: 3/4-in.Ideal: 1 1/2-in.
Properly conditioned hole and mud
Gaugediameter
No sloughing
Uniform as possible( no washouts or restrictions)
NO FLOWNO LOSSES
Casing centered in borehole
Accurate BHST and BHCT
6/SRPC/
Cementing Problems• Placement (mud removal)
– Poor centralization -> channel
– Incorrect flow regime -> channel, mud film, fluid contamination
• After placement before setting– Slurry segregation: free water and/or
settling
– Formation fluid invasion: gas or water
– Debonding (microannulus)
– Water loss
– Permeable formation interactions
• After placement once set– Debonding
– Mechanical failure (Pressure, temperature, drilling, tectonics,..)
7/SRPC/
Cement Evaluation Methods
• Hydraulic testing
• Temperature, nuclear (cement top)
• Acoustic
– Sonic (CBL/VDL, CBT): omnidirectional
– Ultrasonic (USI): high resolution image
• Analysis of cement job data
8/SRPC/
Cement Evaluation with the UltraSonic
Imager
• Introduction
• Acoustic methods basics
– Acoustic impedance
– CBL/VDL
– USI
• USI tool basics
• USI QC
• USI and CBL/VDL interpretation
• Integrating logs and cementing data
9/SRPC/
Acoustic impedance
Z MRayl
0
2
4
6
8
Heavymud
Water
Oil
Gas
Neat
Light
Cement Contaminated
Cement
Setting
slurry
Liquid
Materials
• Acoustic tools respond to acoustic impedance (acoustic hardness) Z
• Z = density x acoustic velocity• Z is expressed in MRayl (106 kg.m-2.s-1)
10/SRPC/
Lightweight cements
• Generally speaking they are more difficult to evaluate– Lower acoustic impedance
– Slower setting (longer waiting time)
• For a given density all lightweight cements are not alike– Dowell LiteCRETE systems exhibit:
• Low porosity (low water content) and hence a relatively high ultimate acoustic impedance
• Fast strength development and hence a fast acoustic impedance development (can be logged earlier)
• For a given density they are easier to log than any other lightweight cement
11/SRPC/
Sonic (CBL/VDL) principle
20 kHz
Transmitter
3 ft Receiver
5 ft Receiver
Casing
Formation
t
t
Bonded cement
Mud
Cement
VDL
CBL amplitude
0 100 CBL amp
12/SRPC/
CBL amplitude interpretation
• What is needed? – Expected cement impedance -->
amplitude for 100% bond: E100%
– Free pipe amplitude: EFree
– Measured amplitude: EMeas
• Bond index:
BI = log10(Emeas/Efree)
log10 (E100%/Efree)
• Conventionally:– 80% < BI < 100%: Good cement
– 80% > BI: ?
13/SRPC/
Sonic (CBL/CBT)
Strengths• Most well fluids, tolerates corrosion
• Responds to solidity (shear coupling)
• Qualitative cement-formation bond from VDL
Weaknesses• High CBL amplitude is ambiguous
– liquid microannulus (shear coupling lost)
– channel
– contaminated cement
– light cement mixed with neat
– Fast formation arrivals
– reflections from double string or hard formation
• Low amplitude doesn’t ensure 100% bond
14/SRPC/
UltraSonic Imager Principle
The USI evaluates cement with•An ultrasonic
transducer • The
resonance technique
Free pipe
Good cement
(0.2-0.7 MHz)
15/SRPC/
Ultrasonics (USI) advantages over sonics
(CBL)
• Tolerates liquid microannulus (vibrations normal to surface)
• Full coverage, 30 mm resolution image– Detailed picture of material
distribution: solid, liquid, gas, debonded cement
– Detects narrow channels
• Easier interpretation and less uncertainty than sonics (CBL/CBT)
• Casing inspection in same pass
16/SRPC/
The USI view
Mud channel
WashoutEccentered casing
Gas microannulus
Well centered casing
Perfs
Casing weld
17/SRPC/
Acoustic Evaluation Summary
• Acoustic logs are sensitive to the acoustic properties (especially impedance) of the material in contact with the casing.
• The USI is the primary evaluation tool: the image is easier to interpret and much less ambiguous than the CBL log.
• USI and CBL are sensitive to the cement/casing bond but in different ways- complementary evaluation.
• Acoustic methods are limited in very light cements (low acoustic contrast from mud).
• For optimum evaluation, cement job data must be included in the evaluation because cement does not disappear.
18/SRPC/
Cement Evaluation with the UltraSonic
Imager • Introduction
• Acoustics basics
• USI tool basics
– Measurements and processing
– Tool and specifications
– Logging procedure
– Images
• USI QC
• USI and CBL/VDL interpretation
• Integrating logs and cementing data
19/SRPC/
UltraSonic Imager
• Ultrasonic tool operating between 200 and 700 kHz.
• Full casing coverage at 1.2 in. (30 mm) resolution using rotating transducer
• Measurements
• Cement evaluation
• Casing corrosion and wear
20/SRPC/
USI Measurements
Echo amplitude
(Internal casing condition)
Transit time
Internal radius
Thickness Cement Impedance
21/SRPC/
USI si
gnal pro
cess
ing
22/SRPC/
USI signal processing
Fluid properties measurement (FPM)
Zmud mudV
T3 processing:
Echo amplitude
Travel time
Resonant frequency:
Fractional bandwith:
f0
f0
f
Internalrugosity
Casingthickness
Internalradius
Waveform
Cementimpedance
Fit plane wave model
Correct for cylindrical casing geometry
Casingthickness
Cementimpedance
23/SRPC/
USI tool
Electronics
Sonde
Rotating sub
24/SRPC/
Rotating subs
Assembly Sub O.D.
USRS-A
USRS-B
USRS-C
USRS-D
3.58”
4.64”
6.69”
8.70”
4 1/2” - 5 1/2”
5 5/8” - 7 5/8”
8 5/8” - 9 5/8”
10 3/4” - 13 3/8”
25/SRPC/
USI General Specifications
Length (sonde and cartridge only) 248 in. [6.3 m]
Diameter 3.6 to 11.2 in.
Weight
-Sonde 188 to 210 lb
-Cartridge 153 lb
Maximum temperature rating 350oF [175oC]
Maximum operating pressure 20,000 psi
Recommended logging speed 400 to 3200 ft/hr
Combinable with CBL-VDL, CBT, GPIT, Gamma Ray. CCL
26/SRPC/
USI Measurement Specifications
Casing OD 4.5 - 13.375 in.
Casing thickness 0.17 - 0.59 in. (4.5-15 mm)
Acoustic Impedance 0-10 MRayl
Max. deviation No limit
Logging speed 400 to 3200 ft/hr
Sampling
- Azimuthal 5-10 deg.
- Vertical 0.6-6 in.
Maximum mud weight
-Water-base mud ~16 lbm/gal
-Oil-base mud ~11.6 lbm/gal*
* Depends on composition, temperature and pressure. Good logs are usually obtained up to 13 lb/gal and sometimes up to 16 lb/gal
27/SRPC/
USI Cement Evaluation
Specifications
Acoustic impedance
Range 0-10 MRayl
Resolution 0.2 MRayl
Accuracy
0-3.3 MRayl +/-0.5 MRayl
> 3.3 MRayl +/- 15%
Min. quantifiable channel width
1.2 in. (30 mm)
28/SRPC/
USI logging procedure
1. Measure fluid properties using reference plate while running into well:
- velocity FVEL
- acoustic impedance ZMUD
2. Enter ZMUD and FVEL parameters. Flip transducer to face casing and log up.
29/SRPC/
USI cement image settings
Raw image
Interpreted Image
Cement
Liquid
Gas or dry micro-annulus
Sta
nd
ard
Lig
ht
0
2
4
6
8
Z MRayl
Solid/liquid threshold
ZTCM
Maximum impedance
Gas/liquid threshold
+/- 0.5
The USI discriminates between solid, liquid and gas/dry microannulus using acoustic impedance thresholds.
30/SRPC/
Mud impedance inside casing Zmud
• From FPM (after Q-check versus theoretical value). 0.1 MRayl change in Zmud changes Zcem by ~ 0.5 MRayl.
Cement impedance scale
• Adapt upper limit to cement impedance
USI Parameters
Cement type Density (ppg) Upper Z value(MRayl)
Neat > 13 8Light bentonitic 14 < density < 11.5 5Very light bentonitic < 11.5 4LiteCRETE 14 < density < 11.5 6LiteCRETE < 11.5 5
Liquid/solid threshold ZTCM
• About 0.5 MRayl above impedance of mud in annulus. Typical values:
Slurry density(ppg)
ZTCM (MRayl)
<12.5 *12.5 2.116 2.619 3.1
31/SRPC/
USI combined casing + cement
presentation Casing CementQC
Process flags, Eccentering, CCL, gamma
Processing flags
Amplitude
Casing cross-section
Internal radius
Thickness
Thickness
Cement raw
Cement interpreted
Bond index
Channel
32/SRPC/
USI + CBL/VDL cement presentation
USI VDLQC
Acoustic impedance
Cement image interpreted
VDL
Bond index
CBL, gamma
Process flags, eccentering
CBL
CBL
33/SRPC/
Image orientation
• In deviated wells, interpretation of channels etc. is aided by orienting images upper/lower side of casing
• Orientation tools such as GPIT can be run in combination with the USI and CBL.
• If no orientation tool is run the USI eccentering azimuth curve AZEC is usually a good indication of higher side except in near-vertical wells and S-bends. It is not sufficiently reliable for automatic image orientation.
34/SRPC/
New USI presentations
• Available in OP9.1• Dowell cement header• USI cement with Dowell
cement data • USI and CBL cement with
Dowell cement data• USI combined QC + casing +
cement
35/SRPC/
Dowell cement header
Well
Time
Caliper
original DF
Fluid
Post job events
Logging fluid
Casing
Collars
Set cement properties
36/SRPC/
USI presentation with Dowell cement data
USI
Calipers
Casing standoff
Average USI impedance
37/SRPC/
USI/CBL presentation with Dowell
cementing data
Casing standoff
Calipers
Average USI
impedance
USI
CBL
Predicted CBL for 80% and
100% bond
VDL
38/SRPC/
USI/CBL presentation with Dowell
cementing data Casing standoff
G ray
USI cement CBL
Predicted CBL for 80% and 100% bond
VDLUSI amp
USI ecc
39/SRPC/
Standard USI presentation
Client Log
Dowell Cement Header (if cementing by Dowell)
Standard API Header
SLB Composite/LQC log
Repeat section (Client log)
ZMUD and FVEL plots
Standard API Tail
40/SRPC/
Cement Evaluation with the UltraSonic
Imager • Introduction
• Acoustics basics
• USI tool basics
• USI QC
– FPM check
– QC presentations
– Factors affecting USI response
• USI and CBL/VDL interpretation
• Integrating logs and cementing data
41/SRPC/
USI QC Procedure
• Check fluid properties log (FPM)
• Check QC log for correct echo acquisition
• Check no processing flags
• Eccentering inside spec
• Casing radius and thickness close to nominal in uncorroded areas
• Casing must be in good condition and radius and thickness accurate for a good cement log
42/SRPC/
Fluid Properties Measurement QC
Fluid velocity curve is smooth and consistent with fluid type
Mud impedance is inside theoretical limits with small dispersion
43/SRPC/
Zmud calculation
Clear FluidsZ_FLUID (MRayl) = Rho (g/cm3) * 304.8/Velocity (US/ft)
Rho=downhole density
Check measured Impedance = theory ± 10%
Weighted MudsZ_FLUID (MRayl) =
K * Rho (G/C3) * 304.8 /
Velocity (US/ft )
K - Factor is in the range of 0.85 -1.0. An empirical formula exists for K.
Check measured impedance= theory ± 10%
or +10% - 25% if K not known.
Excel spreadsheet available to check Zmud.
44/SRPC/
USI QC log
Travel Time histogram
Time
Echoes centred in window
Eccentering inside tolerance.
Gain below max
Casing ID close to nominal
Detection window
45/SRPC/
QC of combined casing + cement
images Casing CementQC
Mean casing diameter and thickness agree with nominal, curves don’t straight-line
Processing flags clean
Eccentering inside tolerance
Casing must be in good conditon for good cement log
Amplitude image clean (no rugosity or eccentering)
46/SRPC/
New QC+casing+cement
presentation Casing CementQC
Processing flags clean
Eccentering inside tolerance
Casing must be in good conditon for good cement log
Amplitude image clean (no rugosity or eccentering)
QC
Echoes centred in window
TT histogram
Mean casing diameter and thickness agree with nominal, no straight-lining
47/SRPC/
USI Processing flags
0
1
2
3
4-6
7-10
No problem.
Casing thickness error (thickness and cement impedance invalid).Error fitting model (cement impedance invalid).
Telemetry.
Echo not detected (all data invalid).
Signal too short for processing (thickness and cement impedance invalid).
Flags indicate problems during processing of echo waveforms that may invalidate the data
48/SRPC/
Factors affecting USI response
• Casing shape and rugosity– Normal manufacturing patterns
affect cement image slightly– Wear and corrosion and
extreme manufacturing patterns create artefacts that can be diagnosed by correlations with casing images
• Tool eccentering – < 2 to 4% of casing diameter
(depending on thickness) for < 0.5 MRayl error
• Third interface reflections (outer casing or hard formation)
49/SRPC/
Casing shape effects
Internal manufacturing patterns often affect cement image slightly but do not usually affect interpretationAmp Int rad. Cement
Formation reflections
50/SRPC/
Poor casing condition affects cement
evaluation
Red “Gas” indications
Processing flags
Echo amplitude shows rugosity
Processing flags and amplitude image show that gas indications are an artifact of internal rugosity
QC Casing Cement
51/SRPC/
Casing wear can affect cement image
Drill pipe wear creates false “channel”
QC Casing Cement
False channe
lWear
groove
52/SRPC/
Deformed casing
QC Casing Cement
Deformed casing can cause lost echoes and tool eccentering. Even the eccentering curve becomes false. The log must be repeated with a wider acquisition window.
Max/min TT TT histogram
Echoes outside acquisition
window
Window
Lost echoes
Eccentering
53/SRPC/
Third interface reflections
Int. radius
Thickness Cement
Typical “galaxy” patterns created by interference between casing resonance and reflections from outer casing (here) or hard formation. The patterns indicate good cement except when the casing touches the formation in free pipe.
Narrow side of annulus
Galaxy pattern
Channel
54/SRPC/
Third interface reflections
Casing Cement
No centralizers, 4.5 in. liner inside 7 in. casing
Galaxy patterns on narrow side of annulus
3 centralizers/joint, 7 in. casing in open hole
Tigerskin pattern all round
Collar
Collar
Centralizers
55/SRPC/
Cement Evaluation with the UltraSonic
Imager • Introduction
• Acoustics basics
• USI tool basics
• USI QC
• USI and USI/CBL Interpretation– USI response– USI and CBL/VDL
– Typical images and logs
– Interpretation summary
– Limitations of ultrasonics
• Integrating logs and cementing data
56/SRPC/
USI response to materials in annulus
Good cement +/- 15%impedance(+25% if shear bond)
Liquids/gas +/-0.5 MRayl
Gas microannulus/ drydebond
Reads gas
Liquid layer- < 0.2 mm microannulus
- Mud layer > 0.5 mm
Tolerates 0.1 to 0.2 mm(50% reading with 6 to12 mm casingthickness)
Reads mud
Thin cement Reflections fromsecond casing or hardformation createinterference patterns
57/SRPC/
USI In
terp
reta
tion
58/SRPC/
BP Test well (1)
Channel and contaminated cement
Contaminated cement
Good cement
Channel
Heavily contam. cement
59/SRPC/
BP Test well (2)
Mud cake
Good cement
Mud cake
Outer casing
reflections
60/SRPC/
USI and CBL/VDL
• In simple cases (good well-bonded cement, free pipe, mud channel) the tools agree.
• In more complicated real-life situations the tools have different responses which can aid interpretation:– Contaminated cement– Wet microannulus– Dry microannulus
61/SRPC/
USI and CBL/VDL guide
USI CBL/VDL
Resolution 1.2 in. 360 deg. x 3 ft
Well bondedcement
Cement Cement
Very lightcement
Low contrast[special processingif debonded]
Low contrast frommud
Dry microann.Debondedcement
Dry microann. /gas(special processing)
Good/fair bond
Wet microann. Slightly affected AmbiguousMud layer Channel AmbiguousContaminatedcement
Low-Z cement Ambiguous
Mixed lead/tailcement
Mixed lead/tail Ambiguous
Mud channel Channel Ambiguous
Gas channel Gas channel Cement/ambiguous
Formation bond Not seen VDL qualitative
Outer casing/hard formation
Slightly affected Strongly affected
Casing condition Very sensitive Slightly sensitive
Mud attenuation < 12 dB/cm/MHZ No limit
62/SRPC/
Good cement
USI VDLQC CBL
CBL flat, low
Strong formation
arrival
Weak casing arrival
Mean Z 8 MRayl
63/SRPC/
Mud channel and contaminated cement
USI VDLQC CBL
CBL variable,
high
Weak formation arrival
Strong casing arrival
Channel
Low-Z cement
64/SRPC/
Cement top
USI VDLQC CBL
CBL flat, high
Weak formation arrival
Strong casing arrival
Traces of contaminated
cement
65/SRPC/
Channel and Squeeze
USI BI VDL USI BI VDL
Channel
After squeeze
Perfs
USI
CBL
66/SRPC/
Light cement top
•Light cement has low impedance
•0-4 MRayl scale shows contrast between light cement and liquid
•Liquid/solid threshold set low (2.1) for light cement
•CBL agrees with USI
0-4 MRayl
0 100 Threshold 2.1 MRayl
67/SRPC/
Contaminated cement
Contaminated (low Z) cement: USI image clear, CBL ambiguous
Mud channels: CBL, USI agree
Casing CBLBI
VDL Cement
CBL BI
Weld
CBL BI
USI BI
68/SRPC/
Contaminated medium-weight
cement 0-4 MRayl USI scale brings out small contrasts
Contaminated cement
Liquid
Gas
Liquid
Gas
69/SRPC/
Microannulus/ debond
• A small gap (< 0.2 mm) between casing and cement formed by pressure and temperature changes, or a mud film left on the casing
• USI and CBL respond in different waysMicroannulus USI CBL
Wet Weaklyaffected forgaps <0.1 to0.2 mm
Stronglyaffected
Dry Reads gas.Specialmicro-debondingprocessing
Weaklyaffected forvery small gaps(microns)VDL "bitty"
70/SRPC/
Wet microannulus
USI BI VDL
High CBL
Uniform medium-Z USI
Strong, regular casing arrival
• USI is weakly affected
• CBL reads near free pipe
71/SRPC/
Dry microannulus/ debond
Dry microannulus
Gas microannulus
Dry debond
Micro debond
• Mean the same thing
• Indicate solid cement
• Often occur without gas entry even in double casing strings due to pressure or temperature changes
• Act as a barrier to ultrasound
• Gas entry should only be suspected if in known gas zone, gas injector well near, or gas at surface
72/SRPC/
Gas channel and microannulus
Gas coming to surface of old storage well
Old CBL showed almost 100% bond
New USI showed narrow gas channel plus areas of debond (gas microannulus)
Narrow gas channel
Gas microannulus
Good cement
Raw BI Interp
73/SRPC/
Micro-debonded cement
Patchy “gas”/ cement indicates micro-debonded cement (patchy dry micro-annulus)
Raw BI Interp
74/SRPC/
Extended dry microannulus
(debonded cement)
Debonding can be extensive with low impedance variability and not associated with gas entry
Raw BI Interp
75/SRPC/
Micro-debonding: USI and CBL are
complementary • CBL less affected than USI without
pressure
• USI and CBL improve with pressure
USI BI VDL USI BI VDL
With pressure Without pressure
USI
CBL
76/SRPC/
USI micro-debond logic
Micro-debond presentation Conventional
BI BIMap Map
Automatically classifies patchy low-impedance material as micro-debonded cement
Helps interpretation of light and foam cement
Low CBL
Formation arrivals
CBL VDL
77/SRPC/
Micro-debonded cement processing
HorizontalDeviation
Diagonal 1
Diagonal 2
VerticalDeviation
Transducer“spot” size
If all 4 standard deviations are higher than set thresholds, the current data point is considered to be locally debonded.
78/SRPC/
Micro-debond logic
AI ThresholdsPixel ZMicro-debonding
algorithm Cement
OR
Liquid
Micro-D
OR
Gas
Micro-D
< Thresh
<Thresh
> Thresh
> Thresh
79/SRPC/
Micro-debond logic example
BI Map
Automatically classifies patchy low-impedance material as micro-debonded cement
CBL
CBL VDL
80/SRPC/
Litecrete 12 ppg cement
Debond logic
Threshold map
BI
CBTBI
• Gas entry from known gas zone
• Micro-debond logic shows cement is present
VDL
81/SRPC/
Cement/formation interaction
GR USICBL VDL
GR
• Acoustic logs dependent on lithology
• Cement present throughout
• Contamination ? Microannulus?
82/SRPC/
USI image interpretation
Squeeze
Mud channel
Liquid
?
Narrow
Gas channel
Cement
Dry micro-annulus (Debond)
Extended
No Squeeze
Patchy
High Z
Medium
Light or contam. Cement
Micro-debondedCement
Mud layer + cement
Gas
Cement data
Gas entry if gas zone
Localised
83/SRPC/
Good interpretation
Ambiguous
Very ambiguous or not detectable
Acoustic evaluation at a glance
Cement USI CBL
Heavy, medium, good bond
Very light, good bond
Debonded, drymicroannulus
Liquid microannulus
Mud layer
Mud channel
Contaminated
Gas channel
84/SRPC/
Cement Evaluation with the UltraSonic
Imager
• Introduction
• Acoustic methods basics
• USI tool basics
• USI QC
• USI Interpretation
• Integrating logs and cementing data
– Well and cementing data needed
– Is cement present?
– Are the logs consistent with the data?
– Schlumberger integrated evaluation
85/SRPC/
Integrated analysis
Acoustic logs have limitations. To make the best evaluation the logs must be analyzed together with the well data and cement job data.
86/SRPC/
Well and cement job data needed
• Well data:– Caliper, GR, sonic, directional survey,
temperature, frac pressures– Casings and centralization
• Cement job data:– Density, rheology, pump rates, well
head pressure, mud rheology– Volumes and returns– >> Predictions of cement placement
• Expected cement acoustic impedance– Measured in lab (e.g. UCA)
– From density and database (CBL adviser)
87/SRPC/
Q1: Is cement likely to be present?
• Where is the expected top of cement?– Is the cement log depth far away from
this depth?
• What could have gone wrong?– Were caliper data used to determine
top of cement?– Was the cement volume pumped as
designed?– Did the top plug bump?– Were losses encountered during the
job?– How does the measured wellhead
pressure compare with the predicted one (Job Signature)?
88/SRPC/
Q2: Is the log consistent with the well and cementing
data? (1)• Channel
– Poor pipe centralization?– Poor mud condition before cement
job?• Yield point or gel strength too high?
– Flow rate too low?• Mini. circulation rate to mobilise
mud on narrow side not achieved?
– Washout (caliper)?
• Thick mud film– Good pipe centralization?– Poor mud condition before the
cement job? • Yield point or gel strength too high?
– Flow rate too low?
89/SRPC/
Q2: Is the log consistent with the well and cementing
data? (2) • Contaminated cement / Poorly
set cement:– Not enough bottom plugs?
– Did formation fluid enter during/after the job? (OH logs)
– Cement/permeable formation interactions? (OH logs)
– Temperatures overestimated?
90/SRPC/
Q2: Is the log consistent with the well and cementing
data? (3) • Microannulus / Debonding:
– Did log improve with pressure?
– Is it due to a post job event ?
• Pressure testing of the pipe
• Change of fluid density
• Drilling of next section
– Thin layer of mud/spacer left at the pipe wall (mud condition and flow rate incorrect)?
• Gas entry or gas channel– Is there a known gas zone (OH
logs)?– Is there a gas injection well
near?
91/SRPC/
Schlumberger integrated cementing
and evaluation • Integrating Dowell
cementing and cement job analysis with USI and CBL/VDL wireline logs provides the optimum evaluation.
• In the past cement job analysis was separate from wireline logs.
• Now key well and cementing data can be integrated in the USI/CBL log for a complete evaluation.
92/SRPC/
CBL adviser
Light lead slurry 1200 kg/m3
Tail 1 1900 kg/m3
Tail 2 2000 kg/m3
Fill Impedance CBL amplitude
Attenuation
• Accounts for all well parameters and slurry properties
• Computes expected cement properties and flags misleading situations
93/SRPC/
Schlumberger integrated evaluation
New USI wellsite software allows:
• Automatic inclusion of detailed Dowell cement header
• Inclusion of Dowell well and cementing data:
– Cement density histogram
– Caliper logs
– Calculated pipe standoffs
– Expected cement impedances
– Predicted CBL reading for 100% and 80% bond
94/SRPC/
Dowell cement density histogram
Can be included in USI log
95/SRPC/
Conclusion • The USI provides the most
detailed view of the distribution of cement in the annulus available today.
• The combination with the CBL/VDL is recommended for added confidence, especially when microannulus is present.
• Acoustic logs have limitations.
• Cement evaluation must combine cement job analysis and acoustic logs
• Schlumberger integrated cementing and evaluation is the optimum solution.