1. 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. 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
2/SRPC/

3. 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
3/SRPC/

4. Objectives of cementing
Provide complete isolation of zones (Hydraulic isolation)
Support the casing and protect it from corrosion
4/SRPC/

5. The ideal wellbore Annular gap Minimum: 3/4-in. BHST at top of
Ideal: 1 1/2-in.
BHST at top of
cement
>BHCT at TD
Properly conditioned hole and mud
No sloughing
Gauge
diameter
Uniform as possible
( no washouts or restrictions)
NO LOSSES
NO FLOW
Casing centered in borehole
Thin, impermeable mud filter cake (not gelled or unconsolidated)
Accurate BHST and BHCT
5/SRPC/

6. 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,..)
6/SRPC/

7. 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
7/SRPC/

8. 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
8/SRPC/

9. Acoustic impedance
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)
Materials 2 4 6 8
Neat
Z MRayl
Setting
slurry
Cement
Contaminated
Cement
Light
Heavy
mud
Water
Oil
Gas
Liquid
9/SRPC/

10. 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
10/SRPC/

11. Sonic (CBL/VDL) principle
Casing
Cement
Formation
Mud t
20 kHz
Transmitter
Bonded cement
CBL amplitude
3 ft Receiver t
5 ft Receiver
VDL
CBL amp
11/SRPC/

12. 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: ?
12/SRPC/

13. Sonic (CBL/CBT) Strengths Weaknesses
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
13/SRPC/

14. UltraSonic Imager Principle
The USI evaluates cement with
An ultrasonic transducer
( MHz)
The resonance technique
Free pipe
Good cement
14/SRPC/

15. 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
15/SRPC/

16. The USI view Gas microannulus Casing weld Mud channel Perfs
Well centered casing
Eccentered casing
Washout
16/SRPC/

17. 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.
17/SRPC/

18. 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
18/SRPC/

19. 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
19/SRPC/

20. USI Measurements Echo amplitude Transit time Thickness
Cement Impedance
Internal radius
(Internal casing condition)
20/SRPC/

21. USI signal processing
21/SRPC/

22. USI signal processing Fluid properties measurement (FPM) f f Z V
mud
mud V
Internal
rugosity
Echo amplitude
Travel time
Internal
radius
Waveform
T3 processing:
Casing
thickness
Resonant frequency:
Fractional bandwith: f
Fit plane wave model f
D f
Cement
impedance
Correct for cylindrical casing geometry
Casing
thickness
Cement
impedance
22/SRPC/

23. USI tool
Electronics
Sonde
Rotating sub
23/SRPC/

24. 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” /8”
24/SRPC/

25. USI General Specifications
Length (sonde and cartridge only) 248 in. [6.3 m]
Diameter to 11.2 in.
Weight
-Sonde to 210 lb
-Cartridge 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
25/SRPC/

26. USI Measurement Specifications
Casing OD in.
Casing thickness in. ( mm)
Acoustic Impedance MRayl
Max. deviation No limit
Logging speed to 3200 ft/hr
Sampling
- Azimuthal deg.
- Vertical 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
26/SRPC/

27. USI Cement Evaluation Specifications
Acoustic impedance
Range MRayl
Resolution MRayl
Accuracy
0-3.3 MRayl +/-0.5 MRayl
> 3.3 MRayl +/- 15%
Min. quantifiable channel width
1.2 in. (30 mm)
27/SRPC/

28. 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.
28/SRPC/

29. USI cement image settings
The USI discriminates between solid, liquid and gas/dry microannulus using acoustic impedance thresholds. 2 4 6 8
Raw image
Interpreted Image
Cement
Standard
Light
Z MRayl
Maximum impedance
Solid/liquid threshold ZTCM
+/- 0.5
Liquid
Gas/liquid threshold
Gas or dry micro-annulus
29/SRPC/

30. USI Parameters New 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
New
Liquid/solid threshold ZTCM
About 0.5 MRayl above impedance of mud in annulus. Typical values:
30/SRPC/

31. USI combined casing + cement presentationQC
Casing
Cement
Channel
Bond index
Cement raw
Thickness
Thickness
Internal radius
Cement interpreted
Casing cross-section
Amplitude
Processing flags
Process flags, Eccentering, CCL, gamma
31/SRPC/

32. USI + CBL/VDL cement presentationQC
CBL
USI
VDL
CBL
VDL
Bond index
Acoustic impedance
Cement image interpreted
CBL, gamma
Process flags, eccentering
32/SRPC/

33. 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.
33/SRPC/

34. New USI presentations New 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
34/SRPC/

35. Dowell cement header New Well Time Casing Collars Caliper original DF
Fluid
Set cement properties
Post job events
Logging fluid
35/SRPC/

36. USI presentation with Dowell cement data
New
USI presentation with Dowell cement data
Calipers
USI
Casing standoff
Average USI impedance
36/SRPC/

37. USI/CBL presentation with Dowell cementing data
New
USI/CBL presentation with Dowell cementing data
CBL
VDL
Casing standoff
Average USI impedance
Predicted CBL for 80% and 100% bond
Calipers
USI
37/SRPC/

38. USI/CBL presentation with Dowell cementing data
New
USI/CBL presentation with Dowell cementing data
Predicted CBL for 80% and 100% bond
Casing standoff
USI ecc
USI amp
G ray
USI cement
CBL
VDL
38/SRPC/

39. Standard USI presentation
Standard API Header
Dowell Cement Header (if cementing by Dowell)
Client Log
SLB Composite/LQC log
Repeat section (Client log)
ZMUD and FVEL plots
Standard API Tail
39/SRPC/

40. 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
40/SRPC/

41. 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
41/SRPC/

42. Fluid Properties Measurement QC
Fluid velocity curve is smooth and consistent with fluid type
Mud impedance is inside theoretical limits with small dispersion
42/SRPC/

43. Zmud calculation New Clear Fluids Weighted Muds
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) * / Velocity (US/ft )
K - Factor is in the range of An empirical formula exists for K.
Check measured impedance= theory ± 10%
or +10% - 25% if K not known.
Excel spreadsheet available to check Zmud.
New
43/SRPC/

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

45. QC of combined casing + cement images
Mean casing diameter and thickness agree with nominal, curves don’t straight-line
Amplitude image clean (no rugosity or eccentering)
Processing flags clean
Eccentering inside tolerance
Casing must be in good conditon for good cement log
45/SRPC/

46. New QC+casing+cement presentation
TT histogram
Echoes centred in window
Mean casing diameter and thickness agree with nominal, no straight-lining
Amplitude image clean (no rugosity or eccentering)
Processing flags clean
Eccentering inside tolerance
Casing must be in good conditon for good cement log
46/SRPC/

47. USI Processing flags
Flags indicate problems during processing of echo waveforms that may invalidate the data 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).
47/SRPC/

48. 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)
48/SRPC/

49. Formation reflections
Casing shape effects
Internal manufacturing patterns often affect cement image slightly but do not usually affect interpretation
Amp
Int rad.
Cement
Formation reflections
49/SRPC/

50. Poor casing condition affects cement evaluation
Echo amplitude shows rugosity
Processing flags
Red “Gas” indications QC
Casing
Cement
Processing flags and amplitude image show that gas indications are an artifact of internal rugosity
50/SRPC/

51. Casing wear can affect cement image
Drill pipe wear creates false “channel”
Wear groove
False channel QC
Casing
Cement
51/SRPC/

52. Echoes outside acquisition window
Deformed casing
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.
Window
Echoes outside acquisition window
Max/min TT
TT histogram
Eccentering
Lost echoes QC
Casing
Cement
52/SRPC/

53. Third interface reflections
Narrow side of annulus
Channel
Galaxy pattern
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.
53/SRPC/

54. Third interface reflections
No centralizers, 4.5 in. liner inside 7 in. casing
Collar
Galaxy patterns on narrow side of annulus
3 centralizers/joint, 7 in. casing in open hole
Collar
Tigerskin pattern all round
Centralizers
Casing
Cement
54/SRPC/

55. 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
55/SRPC/

56. USI response to materials in annulus
56/SRPC/

57. New
USI Interpretation
57/SRPC/

58. BP Test well (1) Channel and contaminated cement Good cement
Heavily contam. cement
Channel
58/SRPC/

59. Outer casing reflections
BP Test well (2)
Mud cake
Mud cake
Good cement
Outer casing reflections
59/SRPC/

60. 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
60/SRPC/

61. USI and CBL/VDL guide
61/SRPC/

62. Strong formation arrival
Good cement
Strong formation arrival
CBL flat, low
Mean Z 8 MRayl
Weak casing arrival
USI
VDL QC
CBL
62/SRPC/

63. Mud channel and contaminated cement
Weak formation arrival
CBL variable, high
Strong casing arrival
Channel
Low-Z cement
USI
VDL QC
CBL
63/SRPC/

64. Cement top Weak formation arrival CBL flat, high Strong casing arrival
Traces of contaminated cement
USI
VDL QC
CBL
64/SRPC/

65. Channel and Squeeze Channel After squeeze Perfs USI CBL USI BI VDL USI
65/SRPC/

66. 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
Threshold 2.1 MRayl
66/SRPC/

67. Contaminated cement
Contaminated (low Z) cement: USI image clear, CBL ambiguous
Weld
CBL BI
Mud channels: CBL, USI agree
CBL BI
USI BI
CBLBI
VDL
Casing
Cement
67/SRPC/

68. Contaminated medium-weight cement
0-4 MRayl USI scale brings out small contrasts
Gas
Liquid
Contaminated cement
Gas
Liquid
68/SRPC/

69. 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
69/SRPC/

70. Wet microannulus USI is weakly affected CBL reads near free pipe
Strong, regular casing arrival
High CBL
Uniform medium-Z USI
USI BI
VDL
70/SRPC/

71. Dry microannulus/ debond
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
71/SRPC/

72. Gas channel and microannulus
Narrow gas channel
Gas microannulus
Good cement
Raw BI
Interp
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)
72/SRPC/

73. Micro-debonded cement
Patchy “gas”/ cement indicates micro-debonded cement (patchy dry micro-annulus)
Raw BI
Interp
73/SRPC/

74. Extended dry microannulus (debonded cement)
Debonding can be extensive with low impedance variability and not associated with gas entry
Raw BI
Interp
74/SRPC/

75. Micro-debonding: USI and CBL are complementary
CBL less affected than USI without pressure
USI and CBL improve with pressure
With pressure
Without pressure
CBL
USI
USI BI
VDL
USI BI
VDL
75/SRPC/

76. USI micro-debond logic
New
USI micro-debond logic
Automatically classifies patchy low-impedance material as micro-debonded cement
Helps interpretation of light and foam cement
Micro-debond presentation
Formation arrivals
Conventional
Low CBL BI
Map BI
Map
CBL
VDL
76/SRPC/

77. Micro-debonded cement processing
New
Micro-debonded cement processing
If all 4 standard deviations are higher than set thresholds, the current data point is considered to be locally debonded.
77/SRPC/

78. Micro-debond logic New Liquid Cement Micro-D Gas Micro-D
Micro-debonding
algorithm
Pixel Z
AI Thresholds
Cement
Liquid
< Thresh OR
> Thresh
Micro-D
Gas
<Thresh OR
> Thresh
Micro-D
78/SRPC/

79. Micro-debond logic example
New
Micro-debond logic example
Automatically classifies patchy low-impedance material as micro-debonded cement
CBL BI
Map
CBL
VDL
79/SRPC/

80. Litecrete 12 ppg cement New Gas entry from known gas zone
Micro-debond logic shows cement is present
CBTBI
Debond logic
Threshold map BI
VDL
80/SRPC/

81. Cement/formation interaction
Acoustic logs dependent on lithology
Cement present throughout
Contamination ? Microannulus? GR GR
CBL
VDL
USI
81/SRPC/

82. USI image interpretation
New
USI image interpretation
High Z
Patchy
Gas
Cement
Localised
Medium
Liquid
Micro-debondedCement
Gas entry if gas zone
Light or contam. Cement
Extended
Narrow
Cement data
Dry micro-annulus (Debond)
Mud channel
Mud layer + cement
Gas channel
Squeeze
No Squeeze ?
82/SRPC/

83. Acoustic evaluation at a glance
Good interpretation
Ambiguous
Very ambiguous or not detectable
83/SRPC/

84. 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
84/SRPC/

85. 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.
85/SRPC/

86. 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)
86/SRPC/

87. 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)?
87/SRPC/

88. 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?
88/SRPC/

89. 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?
89/SRPC/

90. 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?
90/SRPC/

91. Schlumberger integrated cementing and evaluation
New
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.
91/SRPC/

92. 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 kg/m3
Tail kg/m3
Fill
Impedance
CBL amplitude
Attenuation
92/SRPC/

93. Schlumberger integrated evaluation
New
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
93/SRPC/

94. Dowell cement density histogram
New
Dowell cement density histogram
Can be included in USI log
94/SRPC/

95. 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.
95/SRPC/