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Cement Bond Log
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Cement Bond LogCement Bond Log
Why Cement Bond Logging?Why Cement Bond Logging?
Evaluate zone-to-zone isolation: Casing to Cement Bond Cement to Formation Bond
Identify cement top Evaluate cement quality after squeeze jobs Correlation log GR-CCL
The Ideal Wellbore The Ideal Wellbore
Thin, impermeable mud filter cake (not gelled or unconsolidated)
Annular gapMinimum: 3/4-in.Ideal: 1 1/2-in.
Properly conditioned hole and mud
Gauge diameter
No sloughing
Uniform as possible( no washouts or restrictions)
NO FLOWNO LOSSES
Casing centered in borehole
Accurate BHST and BHCT
Typical Well Completion Typical Well Completion
Cementing ProblemsCementing 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)
Cement Evaluation MethodsCement Evaluation Methods
• Hydraulic testing• Temperature, nuclear (cement top)• Acoustic
Sonic (CBL/VDL, CBT) Ultrasonic (USI): high resolution image
• Analysis of cement job data
Cement Bond LoggingCement Bond Logging
Zero bond is like ringing a bell Loud ringing (high amplitude sound wave)
Good bond is like a blanket on a bell Low amplitude sound wave
Sonic Path in Cased HoleSonic Path in Cased Hole
Sonic Sonic (CBL/VDL(CBL/VDL
) ) PrinciplePrinciple
20 kHz
Transmitter
3 ft Receiver
5 ft Receiver
CasingFormation
t
t
Bonded cement
Mud
Cement
VDL
CBL amplitude
0 100 CBL amp
CBL - VDLCBL - VDL
CBL measures casing to cement bond VDL indicates cement to formation bond
CBL Free-Pipe ReferenceCBL Free-Pipe ReferenceCasing
sizeWeight (lb/ft)
Expected free-pipe reading
SLS-W SLS-C5 in. 15 245 238 77mV
18 243 23621 241 234
5.5 in. 15.5 254 248 71 mV17 253 24720 251 24523 250 243
7 in. 23 278 271 61 mV 26 276 27029 275 26832 273 26735 272 26538 271 26440 269 262
7.625 in. 26.4 288 282 59 mV29.7 287 28033.7 285 27839 283 276
9.625 in. 40 320 313 52 mV43.5 318 31247 317 310
53.5 315 30810.75 in. 40.5 340 333 50 mV
45.5 339 33248 338 33151 337 33054 336 329
55.5 335 32813.375 in. 48 385 378 47 mV
68 380 373
Estimated transit time (msec)
Effects on CBL and TTEffects on CBL and TT
Effect CBL mV
TT us
Good cement Decrease May increase
No cement Equals FP valueConstant
Channeling Slight increase Constant
Eccentered tool Decrease Erratic
Fast formation Erratic Decrease
Microannulus Increases Constant
Noise Erratic Decrease
Cycle skipping Increase Increase
Casing collars Decrease Slight increase
Stretch Constant Slight increase
LQC, Basic InterpretationLQC, Basic Interpretation
TT is the best LQC CBL = CBSL and TT = TTSL Microannulus makes CBL read higher-
run USIT
LQC, Basic InterpretationLQC, Basic Interpretation
VDL should be railroad tracks in free pipe CBL Free pipe values should be within 5% of
expected free pipe values. At collars, TT & TTSL should increase slightly for 3 ft At collars, CBL & CBSL will decrease Eccentralization will cause TT & TTSL to decrease or
increase In good bond, transit times may increase due to
stretch or cycle skipping You will see clear casing arrival in bad cement
Good CementGood Cement
USI VDLQC CBL
CBL flat, low
Strong formation arrival
Weak casing arrival
Mean Z 8 MRayl
Mud Channel and Contaminated CementMud Channel and Contaminated Cement
USI VDLQC CBL
CBL variable,
high
Weak formation arrival
Strong casing arrival
Channel
Low-Z cement
Cement TopCement Top
USI VDLQC CBL
CBL flat, high
Weak formation arrival
Strong casing arrival
Traces of contaminated
cement
Channel and Squeeze Channel and Squeeze
USI BI VDL USI BI VDL
Channel After squeeze
Perfos
USI
CBL
Microannulus / Debond 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
Microannulus USI CBL
Wet Weakly affected for gaps <0.1 to 0.2 mm
Strongly affected
Dry Reads gas. Special micro-debonding processing
Weakly affected for very small gaps (microns) VDL "bitty"
Good interpretation
Ambiguous
Very ambiguous or not detectable
Acoustic Evaluation at a GlanceAcoustic Evaluation at a GlanceCement USI CBLHeavy, medium, good bondVery light, good bondDebonded, drymicroannulus
Liquid microannulus
Mud layer
Mud channel
Contaminated
Gas channel