The document provides comprehensive information on Cement Bond Logging (CBL) and Variable Density Logging (VDL), focusing on the principles, measurement techniques, and interpretations crucial for assessing cement integrity and isolation in wellbore operations. It highlights the importance of factors like acoustic impedance, transit time, and amplitude in determining the quality of the cement bond. Additionally, it discusses common issues affecting measurements and their implications for cementing operations.

1. CBL-VDL Cement Bond Logging
Basic Theory and Interpretation
British Training Centre

2. 2 KS
British Training Centre
Objectives of Primary Cementing
Casing
Zone Hydraulic Isolation
Oil Zone
Water Zone
Cement
Prevents
•Mixing of unwanted fluids
•Fluids escaping to surface
•Invading fluids [crossflow]
•Casing Corrosion
•Casing Collapse
Shale Zone
Gas Zone

3. 3 KS
British Training Centre
Cement Quality Problems
Casing
No Zone Hydraulic Isolation
Oil Zone
Water Zone
Cement
Causes
•Mixing of unwanted fluids
•Fluids escaping to surface
•Invading fluids [crossflow]
•Casing Corrosion
•Casing Collapse

4. 4 KS
British Training Centre
Environment Description
Top of Cement
Poor Cement to Formation Bond
Formations
Micro-Annulus
Less than perfect cement job.
Two stages Cement job
Double Casing
b
Fluid filled Casing

5. 5 KS
British Training Centre
CBL-VDL Log Applications
Client Needs
Oil Zone
Water Zone
Cement
To Evaluate Cement Job
•Check Integrity of Cement
•To Verify Zone Isolation
•To Determine Cement
Strength
•Is there any Channel ?
•Is it necessary to Repair ?
•Will be possible to Repair?
[ by performing a SQUEEZE ]
•Where is the Top of the
Cement ?
Casing

6. CBL-VDL Cement Bond Logging
Physics of Measurement

7. 7 KS
British Training Centre
Basic Sonic Principle
Basic Tool Principle
– A Transmitter fires an acoustic signal in
all directions
– Surrounding Media Resonates
– Receivers record resulting sound
– Sound wave is Analyzed

8. 8 KS
British Training Centre
Basic CBL Principle
Similar to a Ringing Bell
When Fluid is behind
Casing, pipe is free to
vibrate [ loud sound ]
When the casing is
bonded to hard cement,
casing vibrations are
attenuated proportionally
to bonded surface
Good
Bond
Good
Good
Bond
Bond
No
Cement
No
No
Cement
Cement

9. 9 KS
British Training Centre
CBL Measurement Principle
Basic Tool Configuration
• 1 Transmitter – 2 Receivers
– 3 ft Receiver for CBL Measurement
– 5 ft Receiver for VDL Analysis
• TOOL MUST BE CENTRALIZED
CBL: CEMENT BOND LOG
VDL: VARIABLE DENSITY LOG
3 ft
5 ft
Tx
R3
R5

10. 10 KS
British Training Centre
CBL-VDL Measurement Principle
Acoustic Signal
Time
µs
Amplitude
T0
|--- Resulting Sound--|
- T0 : Firing Pulse
- Resulting Sound: as recorded at the Receivers

11. 11 KS
British Training Centre
CBL Measurement Principle
CBL Definition
• Amplitude of First Arrival in mV
• Measured at 3 ft Receiver
• It is a function of the Casing-Cement Bond
3 ft
Tx
R3
R5
Transit Time Definition
• Time elapsed from T0 to First Arrival
• T T is used as Log Quality Control Indicator

12. 12 KS
British Training Centre
CBL Qualitative Meaning
Good
Bond
Good
Good
Bond
Bond
No
Cement
No
No
Cement
Cement
HIGH CBL signal strength => pipe is free to vibrate [ no cement ]
LOW CBL signal strength => atennuated energy [ cement is present]

13. 13 KS
British Training Centre
Sound to Signal
• Magnetostrictive transducer (Tx)
A high current is passed through a coil surrounding a magnetic material
introducing a strain and causes a ticking sound (Joule effect)
∆L / L
• Piezoelectric transducer (Rx)
Polarized ceramic crystals in the sonde produce voltage when exposed to
strain (Villari effect)
strain
voltage
Unstrained
crystal

14. 14 KS
British Training Centre
CBL Amplitude Vs. Receivers Spacing

15. CBL-VDL Cement Bond Logging
Gate Settings
British Training Center

16. CBL Measurement Gates
WARNING
- The CBL represents one of the most common logs prone to human error
- Incorrect setting of parameters can cause an invalid log
- If CBLF is presented, particular attention must be paid to the selection of FCF

17. 17 KS
British Training Centre
CBL Measurement T0_Delay Mode
(Fixed Gate Mode)
NMSG
CBLG
NMSG: Near Minimum Sliding Gate CBLG : CBL Gate
Set by user at expected T T – 10 µs Opens at NMSG and lasts CBLG µs

18. 18 KS
British Training Centre
CBL Measurement TX Mode
(Back-up for the T0_Delay Mode)
SGW: Sliding-Gate Width
SGW
SGCW
SGCW : Sliding-Gate Closing Width
Sliding Gate opens at SGW µs BEFORE previous detected TT and closes
SGCW µs after current TT
TTSL
AMSG
AMSG :Auxiliary Minimum Sliding Gate
Amplitude is CBSL, Transit Time is TTSL

19. 19 KS
British Training Centre
CBL Measurement Principle
CBL
CBL Definition
Definition
•
• Measured at
Measured at 3
3 ft Receiver
ft Receiver
•
• Amplitude
Amplitude in
in mV of First Arrival
mV of First Arrival
Tranit
Tranit Time
Time Definition
Definition
•
• Time
Time elapsed from
elapsed from T0
T0 to First Arrival
to First Arrival

20. 20 KS
British Training Centre
CBL Time Gates
NMSG: Near Minimum Sliding Gate
CBLG
NMSG
CBLG : CBL Gate
Set by user at T T – 10 µs Opens at NMSG and lasts CBLG µs

21. 21 KS
British Training Centre
The VDL Signal
VDL: VARIABLE DENSITY LOG
• 5 ft Receiver for VDL Analysis
• Allows easy differentiation between
casing and formation arrivals
5 ft
Tx
R3
R5

22. 22 KS
British Training Centre
VDL Algorithm Principle
• Recorded Waveform at one depth
• Waveform is cut for only Positive Peaks
• Peaks are compared to a Grey Scale
• Peaks are shaded and presented from
Top View
• Final Picture Vs Depth is obtained

23. 23 KS
British Training Centre
∆T Casing = 57 µsec/ft
∆T Cement = 75 µsec/ft
∆T Formation ≈ 100 µsec/ft
∆
T
F
l
u
i
d ≈
1
8
9
µ
s
e
c
/
f
t
S
l
o
w
n
e
s
s
P
r
o
p
a
g
a
t
i
o
n
o
f
t
h
e
A
c
o
u
s
t
i
c
E
n
e
r
g
y
d
i
s
t
a
n
c
e
V
e
l
o
c
i
t
y
=
t
i
m
e
1 t
i
m
e
S
l
o
w
n
e
s
s
=
∆t
=
=
v
e
l
o
c
i
t
y
d
i
s
t
a
n
c
e
T
i
m
e
r
e
q
u
i
r
e
d
f
o
r
s
o
u
n
d
t
o
t
r
a
v
e
l
1
f
o
o
t

24. 24 KS
British Training Centre
The amount of sound transmitted between
two different materials depends on their
acoustic impedance difference
Water
Steel
Cement
Sound
Z1
Z2
Acoustic impedance (Z) defined as:
Z = ρ . v
ρ: density of material
V: velocity of sound on that material
Propagation of the Acoustic Energy cont’d
1. If Z1/Z2 is high ==> low transmittance
1. If Z1/Z2 is low ==> high transmittance

25. Waveform Time Analysis
CASING ARRIVALS
TRAVEL TIME
2”
∆T Casing = 57 µsec/ft
∆T Cement = 75 µsec/ft
∆T Formation ≈ 100 µsec/ft
∆T Fluid ≈ 189 µsec/ft
TTC = FLUID + CASING + FLUID
3 in x 189 µs/ft 3 in x 189 µs/ft
= + 3 ft x 57 µs/ft +
12 in/ft 12 in/ft
= 265.5 µs
25 KS
British Training Centre

26. Waveform Time Analysis
FORMATION ARRIVALS
TRAVEL TIME
2”
∆T Casing = 57 µsec/ft
∆T Cement = 75 µsec/ft
∆T Formation ≈ 100 µsec/ft
∆T Fluid ≈ 189 µsec/ft
TTF = FLUID + CEMENT + FORMATION + CEMENT + FLUID
3 in x 189 µs/ft + 2 in x 75 µs/ft
= 2 x + 3 ft x 100 µs/ft
12 in/ft
= 419.5 µs
26 KS
British Training Centre

27. Waveform Time Analysis
FLUID ARRIVALS
TRAVEL TIME
2”
∆T Casing = 57 µsec/ft
∆T Cement = 75 µsec/ft
∆T Formation ≈ 100 µsec/ft
∆T Fluid ≈ 189 µsec/ft
TTf = FLUID
= 3 ft x 189 µs/ft
= 567.0 µs
27 KS
British Training Centre

28. 28 KS
British Training Centre
CBL-VDL Standard Outputs Presentation
•Transit Time TT in micro-seconds [µs]
•CBL Amplitude in millivolts [mV ]
•VDL Variable Density Log [wafeform visual representation]
0 CBL 100
[mV]
400 TT 200
[µs]
200 VDL 1200
[µs]
GR
CCL

29. 29 KS
British Training Centre
CBL-VDL Standard Outputs
•Transit Time TT in micro-seconds [µs]
Log Quality Control
•CBL Amplitude in millivolts [mV ]
Quantitative Measurement of waveform energy
•VDL Variable Density Log [waveform visual representation]
Qualitative Analysis of sound
Qualitative indicator of the presence of solid materials behind the casing
•Gamma Ray and CCL as auxiliary curves for Correlation

30. CBL-VDL Cement Bond Logging
Factors affecting the Log
British Training Centre

31. 31 KS
British Training Centre
Stretching
E1 decreases and TT is detected on a non linear portion of E1
∆T STRETCHING is the TT increase from its value in free pipe
In cases of Good Cement
Threshold
E1
T0
TT
Free Pipe Signal
TT’
∆T
Good Bond Signal

32. 32 KS
British Training Centre
TT Cycle Skipping
E1 could not reach Detection Threshold Level
T T skips to 3rd Peak [E3 ]........this is known as CYCLE SKIPPING
In cases of very Good Cement
Threshold
E1 E3
E2
T0
TT TT’

33. 33 KS
British Training Centre
CBL Time Gates
E1 does not reach Detection Threshold Level
T T skips to 3rd Peak [E3 ]........this is known as CYCLE SKIPPING
Threshold
E3
T0
TT TT’

34. 34 KS
British Training Centre
WF Viewer & Amplitude Measurements
CB3G
TT
CBLG

35. CBL-VDL Cement Bond Logging
Basic Interpretation

36. 36 KS
British Training Centre
Free Pipe Amplitude
T
5
3
2
• If no Casing-Cement bond,
amplitude is not attenuated
• This is called
FREE PIPE AMPLITUDE
CBL: Free Pipe

37. 37 KS
British Training Centre
CBL AMPLITUDE VS. CASING SIZE

38. 38 KS
British Training Centre
CBL-VDL Fluid Effects

39. 39 KS
British Training Centre
FREE PIPE CHECK
CBL
Interpretation
Chevron Patterns
Chevron Patterns
Perfect
Depth Match
TT and CBL Amplitude
as espected according to Casing Size
100
100

40. 40 KS
British Training Centre
Cement to Casing Bond
T
5
3
2
• If casing is well bonded,
soundwave will be attenuated
• The received CBL amplitude will
be low
CBL: Free Pipe
CBL: Good Bond

41. 41 KS
British Training Centre
Open-Hole VDL’s (Before Casing)
GR WF1 VDL
(Standard VDL)
WF2 VDL

42. 42 KS
British Training Centre
Cased-Hole VDL’s (After Casing)
GR WF1 VDL
(Standard VDL)
WF2 VDL
CCL

43. 43 KS
British Training Centre
CBL
Interpretation
GOOD BOND TO CASING & FORMATION
X
X
Transit Time
with some
Stretching
Formation Arrivals
X
No
Casing Arrivals
Low
<----------------------------------------CBL Amplitude

44. 44 KS
British Training Centre
Irregular Bond
T
5
3
2
• The more “free” pipe or
“contaminated” cement in an
interval, the poorer the bond
• If cement job is not perfect, the
amplitude decreases less
CBL: Poor Bond

45. 45 KS
British Training Centre
CBL
Interpretation
POOR BOND TO CASING
X
X
X
Stable
Transit Time
Strong
Casing Arrivals
Medium
<------------------------------CBL Amplitude

46. 46 KS
British Training Centre
CBL
Interpretation
GOOD BOND CASING NOT TO FORMATION
X
X
Transit Time
with some
Cycle Skipping
No
Formation Arrivals
Low
<----------------------------------------CBL Amplitude
No
Casing Arrivals

47. 47 KS
British Training Centre
Micro Annulus
T
5
3
2
• Gap between Casing and Cement
Caused by contraction of casing after
cement sets if Casing Fluid is changed
• E1 amplitude resembles a poorer bond
than actual
• Only a pressure pass can be done to
eliminate the micro annulus
CBL: Poor Bond

48. 48 KS
British Training Centre
Tool Eccentering
Causes for Eccentralization
5
3
2
T
• Improper Equipment selection
[ Centralizers ] for Casing Size
• Missing or Broken Centralizer(s)
• Weak Centralizers in deviated wells
• Tool Damaged and/or bent
• Damaged Casing
Consequences
• Unbalanced sound paths
• Resulting waveform is meaningless

49. 49 KS
British Training Centre
Eccentering Analysis
There will be destructive interference from different sound paths
Waveform from close tool side to casing
If the tool is eccentered
Threshold
T0
TT
Short Path Waveform
Resulting Waveform
Waveform from far tool side to casing
Delayed Waveform
Result is a Bad Log
not recoverable
in Playback
Normal Waveform
Resulting waveform has Dramatic lower amplitude
Resembling a zone of Good Cement but with shorter Transit Time [≈ 4 µs less]

50. 50 KS
British Training Centre
Eccentering
If the tool is eccentered
Threshold
T0
TT
Resulting Waveform Normal Waveform
There will be destructive interference from different sound paths
Waveform from close tool side to casing
Waveform from far tool side to casing
Result is a Bad Log
not recoverable
in Playback
Resulting waveform has Dramatic lower amplitude
Resembling a zone of Good Cement but with shorter Transit Time [≈ 4 µs less]

51. 51 KS
British Training Centre
CBL Amplitude Vs Tool Eccentering

52. 52 KS
British Training Centre
Fast Formation
T
5
3
2
Fast Formation Arrivals
In cases of good cement and
formation slowness < steel slowness
formation arrival arrives first
The transit time and CBL amplitude
will be affected
∆T Dolomite = 43.5 µsec/ft
∆T Limestone = 47.5 µsec/ft
∆T Anhydrate = 50.0 µsec/ft

53. CBL
Interpretation
FAST FORMATION
High
<----------------------------------------CBL Amplitude
on areas of
fast formation
<---------------------------------------- arrivals
Transit Time
Shorter than
Casing arrivals
53 KS
British Training Centre

54. 54 KS
British Training Centre
CBL Quantitative Interpretation
• ATTENUATION
– Logarithm of E1 amplitude [first peak of CBL waveform]
• BOND INDEX
Attenuation in zone of interest [dB/ft]
BI =
Attenuation in Cemented Section [dB/ft]

55. 55 KS
British Training Centre
Bond Index

56. 56 KS
British Training Centre
Zone Insulation Based on Bond Index
5
5 6
6 7
7 8
8 9
9 10
10
30
30
25
25
20
20
15
15
10
10
5
5
Bond Index = 70 %
Bond Index = 70 %
Bond Index = 60 %
Bond Index = 60 %
Bond Index = 80 %
Bond Index = 80 %
C
a
s
i
n
g
O
.
D
.
[
i
n
]
I
n
t
e
r
v
a
l
[
f
t
]

57. 5
7
K
S
B
r
i
t
i
s
h
T
r
a
i
n
i
n
g
C
e
n
t
r
e
C
B
L
Q
u
a
n
t
i
t
a
t
i
v
e
I
n
t
e
r
p
r
e
t
a
t
i
o
n
Q
u
a
n
t
i
t
a
t
i
v
e
I
n
t
e
r
p
r
e
t
a
t
i
o
n
I
n
t
e
r
p
r
e
t
a
t
i
o
n
M
1
C
h
a
r
t
C
a
s
i
n
g
D
a
t
a
O
.
D
.
7
”
,
2
9
l
b
m
/
f
t
C
e
m
e
n
t
C
o
m
p
r
e
s
i
v
e
S
t
r
e
n
g
t
h
3
0
0
0
p
s
i
C
a
s
i
n
g
T
h
i
c
k
n
e
s
s
[
f
r
o
m
t
a
b
l
e
s
]
.
4
0
8
i
n
C
B
L
v
a
l
u
e
f
o
r
1
0
0
%
B
o
n
d
[
m
i
n
i
m
u
m
e
x
p
e
c
t
e
d
a
m
p
l
i
t
u
d
e
]
7
0
%
B
o
n
d
I
n
d
e
x
?
C
B
L
v
a
l
u
e
f
o
r
7
0
%
B
o
n
d

58. 58 KS
British Training Centre
CBL Quality Control
• Is the tool normalized?
• Are the CBL gate parameters set properly?
• Is the measured Transit Time as expected?
• Is the free pipe measured CBL value as expected?
• Is the tool properly centered?
• How does the lowest measured amplitude of the log compare to the
predicted amplitude of the CBL?
• Does the tool response repeat itself (Repeat section)?

59. 59 KS
British Training Centre
CBL Qualitative Interpretation
CONDITION TRANSIT TIME CBL AMPLITUDE VDL
Free Pipe NORMAL HIGH Casing Arrivals
Usually No Formation Arrivals
Good Bond to Casing & Formation HIGH / NOISY LOW No Casing Arrivals
Formation Arrivals
Good Bond to Casing
Not to Formation
HIGH
CAN BE NOISY
LOW No Casing Arrivals
No Formation Arrivals
Poor Bond to Casing NORMAL MEDIUM Strong Casing Arrivals
No Formation Arrivals
Microannulus NORMAL MEDIUM Formation Arrivals
Casing Arrivals
Channeling NORMAL MEDIUM Formation Arrivals
Casing Arrivals
Fast Formations LOW HIGH Formation Arrivals
No Casing Arrivals
Eccentered Tool LOW LOW DEPENDS