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