Cement Evaluation

CASING & CEMENTING
Cement Evaluation

CEMENT EVALUATION
 Determine if the material behind the pipe
is a solid or liquid
 There is no such a thing as “bad cement”
or “good cement.”

EVALUATION TECHNIQUES
1. Radioactive Tracer Survey
2. Hydraulic Testing
3. Temperature Survey
4. Acoustic Logging

RADIOACTIVE TRACERS
• Radioactive tracer work is very rare in
cementing evaluation and requires specialty
equipment and personnel
• Generally used only in very special
applications

PRESSURE EVALUATION
• The most common method of cement
evaluation is to perform some type of
pressure evaluation to determine if
isolation has been achieved

TEMPERATURE LOGS
 Temperature surveys (logs) are very effective
but must be run within a specific time window
to be valid
 Very cost effective
 Limited application

TEMPERATURE SURVEY
 The Heat of hydraiton
causes a temperature
rise
 Compare results with
caliper

Class A
With 100 o
F 120 o
F 140 o
F 160 o
F
0 % Gel 8-12 8-12 6-9 4-8
4 % Gel 8-12 8-12 6-9 4-8
8 % Gel 9-12 9-12 6-9 6-9
12 % Gel 9-12 9-12 9-12 9-12
Time (h)
Example table for determining the time after
cementing to run a temperature log
TEMPERATURE SURVEY

ACOUSTIC LOGGING
 Noise Logging
 Detects noise from moving fluids
 Not continuous
 Sonic Tools
 Conventional bond logs
 Ultrasonic tools
 USIT, CAST V

20 kHz
Transmitter
3 ft
Receiver
5 ft
Receiver
t
t
Bonded cement
VDL
CBL amplitude
0 100
CBL amp
CBL

CBL (SONIC) SIGNAL TRANSMISSION

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: ?
CBL

Strengths
Most well fluids, tolerates corrosion
Responds to solidity (shear coupling)
Qualitative cement-formation bond from VDL
Inexpensive
CBL

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
CBL

The USI evaluates
cement with an
ultrasonic
transducer (0.2 -
0.7 MHz)
Ultrasonic Tools
Solids
behind
pipe
Free Pipe

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.
USI logging procedure

Raw
image
Interpreted
Image
Cement
Liquid
Gas or dry micro-
annulus
Standard
Light
0
2
4
6
8
Z
MRayl
Solid/liquid
threshold
ZTCM
Maximum
impedance
Gas/liquid
threshold
+/- 0.5
USI cement image settings

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.
Max mud weight
-Water-base mud ~16 lbm/gal
-Oil-base mud ~11.6 lbm/gal*
* Depends on composition, temp. and pressure. Good logs can be
obtained up to 13 lb/gal and in rare cases to 16 lb/gal
Measurement Specifications

Tolerate liquid (wet) 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
Ultrasonic Tools

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.
Summary

SUMMARY
• Type of evaluation depends on the
need
• For top of cement
• use temperature if less than 24
hours
• use CBL if more than 24 hours

SUMMARY
• Conventional CBL vs. Focused Tools
• CBL is an average but improved data
from focused tools
• Can identify areas of no cement and
identify channel, but is must be large.
• Both tools have same limitations

SUMMARY
• Sonic vs. Ultrasonic
• Cost of ultrasonic is higher (+ 50 %)
• Quality of data is significantly better
• Do not depend on the computer to do the
interpretation with Ultrasonic Logs

• 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.
Summary

Conclusion
In the absence of cement job data, the slurries
pumped, and formations involved, cement
evaluation is very difficult and subject to
extreme interpretation errors.

COMMON QUESTIONS
I have a well that is making water and I need
to run a cement evaluation log to determine
where the water is coming from. What is the
best log ?
I need to be sure I have isolation, but I can
not spend the money on a decent log. What
can I do ?

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

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

ACOUSTIC IMPEDANCE
Z MRayl
0
2
4
6
8
Heavy
mud
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)

LIGHTWEIGHT CEMENTS
• Generally speaking they are more difficult to
evaluate
– Lower acoustic impedance
– Slower setting (longer waiting time)
• For a given density all lightweight cementsare 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

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

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: ?

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

OUTLINE CBL-VDL
Introduction to Cementing
 Role of cementing
 Mechanics
 Sonic as a Cement Evaluation
tool
 Hardware
 Operations
 Parameters & Setup
 LQC & Hints
 Normalization
 Safety
 Factors effecting tool response
 Log Example

ROLE OF PRIMARY CEMENTING
Conductor Casing (spudded)
Isolate loose surface sediments
Avoid surface corrosion
Surface Casing
Isolate sweet water zones
Mounting rig BOP and
later CSG strings
Oil string (Casing/Liner)
Isolate production zones
Avoid hydrocarbon loss to thief zones
Reduce water production
Intermediate Casing
Isolate loose or high pressure formation
Typical casing string

b
Environment
Fluid filled casing
Cement top.
Poor cement to formation bond.
(example: due to mud-cake)
Formation
Micro-Annulus due to expansion of
casing during cement job.
Less than perfect cement job.
Two stage cement job.
Double Casing

ROLE OF SECONDARY CEMENTING
Repair defects in primary cementing job
L Unsuccessful primary cementing
L Casing corrosion, leaking, split
L Isolate water production in old well

CAUSES OF BAD CEMENTING
Mechanical problems
L Poor pipe centralisation
L Hole conditions: Poor removal of mud from around pipe
Channels or missing cement
Pressure problems
L Influx of formation fluid
L Loss of cement into permeable zone: Permeable, weakened or missing cement
Micro-and cement annulus (Casing flexing contraction)
L Changes in pressure inside casing before setting
L Over pressuring the casing after cement setting
ã May not isolate over gas zones

WHY RUN CBL-VDL
• Primary application is to evaluate the quality of
the casing cement job
• Secondary but equally important application is
to depth match the open hole GR to the cased
hole CCL
• The CBL-VDL-GR-CCL becomes the cased hole
base log to which all subsequent work is depth
referenced.

SONIC PATH IN CASED HOLE
• CBL measures casing to cement bond
• VDL indicates cement to formation bond if casing to
cement bond is good

Cement to Casing Bond
If the casing is well bonded, the
sound will be attenuatedas it travels
through the casing
The received amplitude will be low
We measure E1 amplitude and call it
CBL
CBL: Poor Bond
CBL: Good Bond
Transit Time (TT)
2
4
3
1

Free Pipe Amplitude
If there is no cement bonded to the
casing, then the amplitude will not
be attenuated.
This is called the free pipe
amplitude.
CBL: Free Pipe
2
4
3
1

Less Than Perfect Bond
The more “free” pipe or
“contaminated” cement in an interval
, the poorer the bond.
If the cement job is not perfect, the
amplitude will not decrease as
much.
CBL: Poor Bond
2
4
3
1

SOUND TRANSMISSION
Water
Steel
Cement
Sound
The amount of sound transmitted depends on the acoustic
impedance (Z) difference between the two materials
•If Z1/Z2 is high, low transmittance
•If Z1/Z2 is low, high transmittance
Z1
Z2

SONIC PATH IN CASED HOLE
VDL
CBL

5FT VDL
 5ft VDL gives deeper depth of investigation than 3ft CBL
 5ft VDL indicates cement to formation bond if casing to
cement bond is good

EXPECTED FREE PIPE CBL VALUES
Casing
size
Weight
(lb/ft)
Expected
free-pipe
reading
SLS-W SLS-C
5 in. 15 245 238 77mV
18 243 236
21 241 234
5.5 in. 15.5 254 248 71 mV
17 253 247
20 251 245
23 250 243
7 in. 23 278 271 61 mV
26 276 270
29 275 268
32 273 267
35 272 265
38 271 264
40 269 262
7.625 in. 26.4 288 282 59 mV
29.7 287 280
33.7 285 278
39 283 276
9.625 in. 40 320 313 52 mV
43.5 318 312
47 317 310
53.5 315 308
10.75 in. 40.5 340 333 50 mV
45.5 339 332
48 338 331
51 337 330
54 336 329
55.5 335 328
13.375 in. 48 385 378 47 mV
68 380 373
Estimated transit
time (msec)
(ETT)
These values are for water filled casing
Refer to WRM: DSLT table 7

FACTOR EFFECTING TOOL RESPONSE
 Eccentering
 Cycle skipping
 Fast Formation
(if good cement)
 Fluid Type
 Stretch
 Casing Size
Cement quality!

Eccentering
As in open hole, the amplitude is
dramatically decreased when the
tool is eccentered.
This will give show an incorrectly
good bond.
Since the travel distance is
decreased, the transit time will also
decrease.
Transit Time (TT)
A bad log which
cannot be played back.
2
4
3
1

ECCENTRICITY EFFECTS
 Eccentering by 0.5” reduces amplitude to 30%
 It is crucial to have a well-centralized tool for good CBL data

CYCLE SKIPPING
 Very common in good cement bond (low
amplitude E1)

Micro Annulus
A micro annulus is caused by the
expansion of the casing under
pressure during cementing.
E1 amplitude is larger than it should
be (poorer bond than actual)
A pressure pass can be used to
eliminate the micro annulus.
CBL: Poor Bond
2
4
3
1

INTERPRETATION HINTS
VDL
TYPE OF BOND CBL CASING FORMATION
AMPLITUDE ARRIVALS ARRIVAL
Free Pipe High Large Very Weak or none
Good Casing -
to - Cement - Low Weak Strong
to - Formation
Good Casing Bond
- Poor Formation Bond Low Moderate to Weak Weak or none
Microannulus, Channeling,
Thin Cement Sheath High Moderate Moderate
Fast Formation Arrivals High Absent Strong

Cement to Formation Bond
2
4
3
1

CONCLUSION
CBL – VDL Measurement Provides
L Casing to Cement Bond
L Cement to Formation Bond
L Zonal Isolation
L Channels / Patchy Cement Identification
L Microannulus

ULTRASONIC (USI) ADVANTAGES OVER SONIC
(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

THE USI VIEW
67/SRPC/
Mud
channel
Washout
Eccentered
casing
Gas microannulus
Well
centered
casing
Perfs
Casing weld

ACOUSTIC EVALUATION SUMMARY
• Acousticlogs are sensitive to the acoustic properties
(especially impedance) of the material in contactwith 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- complementaryevaluation.
• Acousticmethods 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.

ULTRASONIC IMAGER
• Introduction
• Acoustics basics
• USI tool basics
– Measurements and processing
– Tool and specifications
– Logging procedure
– Images
• USI QC

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

USI MEASUREMENTS
Echo
amplitude
(Internal
casing
condition)
Transit
time
Internal
radius
Thickness Cement
Impedance

USI SIGNAL PROCESSING
Fluid properties measurement (FPM)
Zmud mud
V
T3 processing:
Echo amplitude
Travel time
Resonant frequency:
Fractional bandwith:
f 0
f 0
D f
Internal
rugosity
Casing
thickness
Internal
radius
Waveform
Cement
impedance
Fit plane wave
model
Correct for cylindrical casing
geometry
Casing
thickness
Cement
impedance

USI TOOL
Electronics
Sonde
Rotating sub

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”

FEATURES AND BENEFITS
 Improved processing ( eliminates the need for free pipe ).
 Can Differentiate fluids behind the casing.
 Gives internal casing radius and image.
 Strong centralization system.
 100% azimuth coverage improves resolution

USIT FAMILY
Service Application
Measurement
USI Cement evaluation Transit time
Baseline corrosion log Amplitude
Casing wear & damage Casing thickness via
casing resonance
Cement
Impedance -T3
UBI High resolution Transit time
Measurements of inner Amplitude
surface of casing &
borehole Borehole geometry &
deformation
Thinbed & fracture analysis
UCI High resolution Transit time
Measurements of casing Amplitude
Inner & outer surface Casing thickness via
Inspection (with thickness) multiple echoes

USI SONDE 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
Maximum mud weight
Water-base mud 16 lbm/gal
Oil-base mud 11.6
lbm/gal
Recommended logging speed (ft/hr)
400 to 3200
Acoustic impedance
Range 0 to 10
MRayl
Resolution 0.2 Mrayl
Casing inside diameter
Range 4.5 to 14 in.
Radius resolution 0.002 in.
Casing thickness
Range 0.18 - 0.59
in
Resolution 0.002 in.

Principle and Measurement
Transducer
Mud Casing Cement
• Acoustic Impedance
• Thickness
• Transit time
• Amplitude of main
echo
• Cement images
• Thickness and
External metal loss
images
• I.D. and Internal
metal loss images
• Images of casing
internal condition
Principle
Measurement

Acoustic Properties of
Materials
Material Density Velocity Acoustic
(Kg/m3) (m/sec) Impedance
(MRay1 106•m-2•sec-1)
Air (1-100 bar) 1.3-130 330 0.004-0.04
Water 1000 1500 1.5
Drilling Fluids 1000-2000 1300-1800 1.5-3.0
Cement Slurries 1000-2000 1800-1500 1.8-3.0
Cement (litefil) 1400 2200-2600 3.1-3.6
Cement (classG) 1900 2700-3700 5.0-7.0
Limestone 2500 5000 12

PLANE-WAVE REFLECTION AND TRANSMISSION
COEFFICIENTS
 ACOUSTIC IMPEDANCE Z = Density X Acoustic Velocity
 (For a homogeneous medium)
REFLECTION COEFFICIENT
R = (Z2 -Z1)/(Z2+Z1)
TRANSMISSION COEFFICIENT
T = 1 + R =(2Z2)/Z2+Z1)
Z1 Z2
1
T
R

USI Signal Processing
T-3 : TRAITMENT TRES TOT
➔ Four Basic Outputs
➔ Amplitude
➔ Internal Radii
➔ Thickness
➔ Acoustic Impedance
➔ Internal Radii & Amplitude
➔ From the TIME DOMAIN
➔ Thickness + Acoustic Impedance
➔ From GROUP DELAY in FREQUENCY DOMAIN

ROTATING SUBS
Assembly Sub O.D. Casing Range
USRS-A 3.58” 4 1/2” - 5 1/2”
USRS-B 4.64” 5 5/8” - 7 5/8”
USRS-C 6.69” 8 5/8” - 9 5/8”
USRS-D 8.70” 10 3/4” - 13 3/8”

FPM / Measurement Position
LOGGING POSITION
FPM POSITION

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 350o
F[175o
C]
Maximum operating pressure 20,000 psi
Recommended logging speed 400 to 3200 ft/hr
Combinable with CBL-VDL, CBT, GPIT,
GammaRay. CCL

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

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)

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.

USI CEMENT IMAGE SETTINGS
Raw
image
Interpreted Image
Cement
Liquid
Gas or dry micro-annulus
Standar
d
Light
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.

USI PARAMETERS
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
C e m e n t t y p e D e n s i t y ( p p g ) U p p e r Z v a l u e
( M R a y l )
N e a t > 1 3 8
L i g h t b e n t o n i t i c 1 4 < d e n s i t y < 1 1 . 5 5
V e r y l i g h t b e n t o n i t i c < 1 1 . 5 4
L i t e C R E T E 1 4 < d e n s i t y < 1 1 . 5 6
L i t e C R E T E < 1 1 . 5 5
Liquid/solid threshold ZTCM
• About 0.5 MRayl above impedance of mud in annulus.
Typical values:
S l u r r y d e n s i t y
( p p g )
Z T C M ( M R a y l )
< 1 2 . 5 *
1 2 . 5 2 . 1
1 6 2 . 6
1 9 3 . 1

USI COMBINED CASING + CEMENT PRESENTATION
Casing Cement
QC
Process flags, Eccentering, CCL, gamma
Processing flags
Amplitude
Casing cross-section
Internal radius
Thickness
Thickness
Cement raw
Cement
interpreted
Bond index
Channel

USI + CBL/VDL
CEMENT PRESENTATION
USI VDL
QC
Acoustic impedance
Cement image interpreted
VDL
Bond index
CBL, gamma
Process flags, eccentering
CBL
CBL

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.

DOWELL CEMENT HEADER
Well
Time
Caliper
original DF
Fluid
Post job events
Logging fluid
Casing
Collars
Set cement properties

USI PRESENTATION WITH DOWELL CEMENT
DATA
USI
Calipers
Casing standoff Average USI
impedance

USI/CBL PRESENTATION WITH DOWELL
CEMENTING DATA
Casing
standoff
Calipers
Average USI
impedance
USI
CBL
Predicted
CBL for 80%
and 100%
bond
VDL

USI/CBL PRESENTATION WITH DOWELL
CEMENTING DATA
Casing
standoff
G ray USI cement CBL
Predicted CBL for
80% and 100% bond
VDL
USI
amp
USI
ecc

STANDARD USI PRESENTATION
Client Log
Dowell CementHeader (if
cementing by Dowell)
Standard API Header
SLB Composite/LQC log
Repeatsection(Client log)
ZMUD and FVELplots
Standard API Tail

ULTRASONIC IMAGER
• Introduction
• USI tool basics
• USI QC
– FPM check
– QC presentations
– Factors affecting USI response

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

FLUID PROPERTIES MEASUREMENT QC
Fluid velocity curve
is smooth and
consistent withfluid
type
Mud impedance is
inside theoretical
limits with small
dispersion

ZMUD CALCULATION
Clear Fluids
Z_FLUID (MRayl) = Rho (g/cm3) * 304.8/Velocity (US/ft)
Rho=downhole density
Check measured Impedance = theory ± 10%
Weighted Muds
Z_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.

USI QC LOG
Travel Time
histogram
Time
Echoes centred
in window
Eccentering inside
tolerance.
Gain below max
Casing ID close
to nominal
Detection
window

QC OF COMBINED CASING + CEMENT
IMAGES
Casing Cement
QC
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)

NEW QC+CASING+CEMENT PRESENTATION
Casing Cement
QC
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

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

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)

CASING SHAPE EFFECTS
Internal manufacturing patterns often affect
cement image slightly but do not usually affect
interpretation
Amp Int rad. Cement
Formation
reflections

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

CASING WEAR CAN AFFECT CEMENT
IMAGE
Drill pipe wear creates false “channel”
QC Casing Cement
False
channel
Wear groove

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

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

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

ULTRASONIC IMAGER
• Introduction
• 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

USI RESPONSE TO MATERIALS IN
ANNULUS
G o o d c e m e n t + / - 1 5 % i m p e d a n c e
( + 2 5 % i f s h e a r b o n d )
L iq u id s / g a s + / - 0 .5 M R a y l
G a s m ic r o a n n u lu s / d r y
d e b o n d
R e a d s g a s
L iq u id la y e r
- < 0 .2 m m m ic r o a n n u lu s
- M u d la y e r > 0 .5 m m
T o l e r a t e s 0 .1 t o 0 .2 m m
( 5 0 % r e a d i n g w i t h 6 t o
1 2 m m c a s i n g
t h i c k n e s s )
R e a d s m u d
T h in c e m e n t R e f l e c t i o n s f r o m
s e c o n d c a s i n g o r h a r d
f o r m a t i o n c r e a t e
i n t e r f e r e n c e p a t t e r n s

BP TEST WELL (1)
Channel and contaminated cement
Contaminated
cement
Good
cement
Channel
Heavily
contam.
cement

BP TEST WELL (2)
Mud cake
Good
cement
Mud
cake
Outer casing
reflections

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

USI AND CBL/VDL GUIDE
U S I C B L / V D L
R e s o lu t io n 1 . 2 i n . 3 6 0 d e g . x 3 f t
W e l l b o n d e d
c e m e n t
C e m e n t C e m e n t
V e r y l ig h t
c e m e n t
L o w c o n t r a s t
[ s p e c i a l p r o c e s s in g
i f d e b o n d e d ]
L o w c o n t r a s t f r o m
m u d
D r y m i c r o a n n .
D e b o n d e d
c e m e n t
D r y m i c r o a n n . / g a s
( s p e c i a l p r o c e s s in g )
G o o d / f a i r b o n d
W e t m ic r o a n n . S l i g h t l y a f f e c t e d A m b i g u o u s
M u d la y e r C h a n n e l A m b i g u o u s
C o n t a m i n a t e d
c e m e n t
L o w - Z c e m e n t A m b i g u o u s
M i x e d l e a d / t a il
c e m e n t
M i x e d l e a d / t a il A m b i g u o u s
M u d c h a n n e l C h a n n e l A m b i g u o u s
G a s c h a n n e l G a s c h a n n e l C e m e n t / a m b i g u o u s
F o r m a t i o n b o n d N o t s e e n V D L q u a l it a t i v e
O u t e r c a s in g /
h a r d f o r m a t i o n
S l i g h t l y a f f e c t e d S t r o n g l y a f f e c t e d
C a s i n g c o n d i t i o n V e r y s e n s i t i v e S l i g h t l y s e n s i t i v e
M u d a t t e n u a t i o n < 1 2 d B / c m / M H Z N o l i m it

GOOD CEMENT
USI VDL
QC CBL
CBL flat, low
Strong formation
arrival
Weak casing arrival
Mean Z 8
MRayl

MUD CHANNEL AND CONTAMINATED
CEMENT
/
USI VDL
QC CBL
CBL
variable,
high
Weak formation arrival
Strong casing arrival
Channel
Low-Z
cement

CEMENT TOP
USI VDL
QC CBL
CBL flat, high
Weak formation arrival
Strong casing arrival
Traces of
contaminated
cement

CHANNEL AND SQUEEZE
USI BI VDL USI BI VDL
Channel After squeeze
Perfs
USI
CBL

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

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

CONTAMINATED MEDIUM-WEIGHT CEMENT
0-4 MRayl USI scale brings out small contrasts
Contaminated
cement
Liquid
Gas
Liquid
Gas

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 ways
M ic r o a n n u lu s U S I C B L
W e t W e a k l y
a f f e c t e d f o r
g a p s < 0 . 1 t o
0 .2 m m
S t r o n g l y
a f f e c t e d
D r y R e a d s g a s .
S p e c i a l
m i c r o -
d e b o n d i n g
p r o c e s s i n g
W e a k l y
a f f e c t e d f o r
v e r y s m a l l g a p s
( m i c r o n s )
V D L "b i t t y "

WET MICROANNULUS
USI BI VDL
High CBL
Uniform
medium-Z USI
Strong, regular
casing arrival
• USI is weakly affected
• CBL reads near free pipe

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

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

MICRO-DEBONDED CEMENT
Patchy “gas”/ cement
indicates micro-debonded
cement (patchy dry micro-
annulus)
Raw BI Interp

EXTENDED DRY MICROANNULUS
(DEBONDED CEMENT)
Debonding can be extensive
with low impedance
variability and not
associated with gas entry
Raw BI Interp

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

USI MICRO-DEBOND LOGIC
Micro-debond
presentation
Conventional
BI BI
Map Map
Automatically classifies patchy low-impedance material as
micro-debonded cement
Helps interpretation of light and foam cement
Low
CBL
Formation
arrivals
CBL VDL

MICRO-DEBONDED CEMENT PROCESSING
H o r i z o n t a l
D e v i a t i o n
D i a g o n a l 1
D i a g o n a l 2
V e r t i c a l
D e v i a t i o n
T r a n s d u c e r
“ s p o t ” s i z e
If all 4 standard deviations are higher than set thresholds, the
current data point is considered to be locally debonded.

MICRO-DEBOND LOGIC
AI Thresholds
Pixel Z
Micro-debonding
algorithm Cement
OR
Liquid
Micro-D
OR
Gas
Micro-D
< Thresh
<Thresh
> Thresh
> Thresh

MICRO-DEBOND LOGIC EXAMPLE
BI Map
Automatically classifies patchy low-impedance
material as micro-debonded cement
CBL
CBL VDL

LITECRETE 12 PPG CEMENT
 Gas entry from known gas zone
 Micro-debond logic shows cement is present
Debond
logic
Threshold
map
BI
CBTBI
VDL

CEMENT/FORMATION INTERACTION
 Acoustic logs dependent on lithology
 Cement present throughout
 Contamination ? Microannulus?
GR USI
CBL VDL
GR

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-
debondedCe
ment
Mud layer
+ cement
Gas
Cement
data
Gas entry if
gas zone
Localised

ACOUSTIC EVALUATION AT A GLANCE
Good interpretation
Ambiguous
Very ambiguous or not detectable
C e m e n t U S I C B L
H e a v y , m e d i u m , g o o d b o n d
V e r y l i g h t , g o o d b o n d
D e b o n d e d , d r y
m i c r o a n n u l u s
L i q u i d m i c r o a n n u l u s
M u d l a y e r
M u d c h a n n e l
C o n t a m i n a t e d
G a s c h a n n e l

ULTRASONIC IMAGER
• Introduction
• Acoustic methods basics
• USI tool basics
• USI QC
• USI Interpretation
– Well and cementing data needed
– Is cement present?
– Are the logs consistent with the data?
– Schlumberger integrated evaluation

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.

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)

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)?

Q2: IS THE LOG CONSISTENT WITH THE
WELL AND CEMENTING DATA? (1)
• Channel
– Poor pipe centralization?
– Poor mud conditionbefore cement job?
• Yieldpoint or gel strength too high?
– Flow rate too low?
• Mini. circulationrate to mobilisemud on narrow side not achieved?
– Washout (caliper)?
• Thick mud film
– Good pipe centralization?
– Poor mud conditionbefore the cement job?
• Yieldpoint or gel strength too high?
– Flow rate too low?

Q2: IS THE LOG CONSISTENT WITH THE WELL AND
CEMENTING DATA? (2)
• Contaminated cement / Poorly set cement:
1. Not enough bottom plugs?
– Did formation fluid enter during/after the job? (OH logs)
– Cement/permeable formation interactions? (OH logs)
– Temperatures overestimated?

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?

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.

CBL ADVISER
 Accounts for all well parameters and slurry properties
 Computes expected cement properties and flags
misleading situations
Light lead slurry
1200 kg/m3
Tail 1 1900 kg/m3
Tail 2 2000 kg/m3
Fill Impedance CBL
amplitude
Attenuation

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

DOWELL CEMENT DENSITY HISTOGRAM
Can be included in USI log

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.

Cement Evaluation

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