A cement bond log (CBL) measures the loss of acoustic energy as it passes through casing to evaluate the integrity of cement bonding between the casing and formation. A sonic tool detects the bond by transmitting acoustic waves and measuring the amplitude of reflected waves, with lower amplitudes indicating better cement bonding. CBLs are used to detect cement bonding, which is important for supporting the casing, preventing fluid leaks, and isolating zones. Interpreters look for intervals of continuous cement bonding indicated by amplitudes below thresholds like 10 mV over a minimum distance.

2. What is it?
CEMENT BOND LOG
(CBL)

3. A cement bond log (CBL) is a type of log
that
measures the loss of acoustic energy as it
passes through casing.
A cement bond log documents an
evaluation of the integrity of cement work
performed on an oil well. In the process of
drilling and completing a well, cement is
injected through the wellbore and rises up
the annulus between the steel casing and
the formation.

4. A sonic tool is typically run on wireline by a service
company that detects the bond of the cement to the
casing and formation via a principle based
on resonance. Casing that is not bound has a higher
resonant vibration than that which is bound, causing
the imparted energy from the sonic signal to be
transferred to the formation. In this sense,
the amplitude of the waveform received is the basic
measurement that is evaluated.

5. CEMENT BOND LOG
(CBL)
What is it used for?

6. Cement bond logs are used to detect the
presence or absence of external cement
behind casing.
Proper cement placement between the well
casing and the formation is essential:
1. To support the casing (shear bond)
2. To prevent fluid from leaking to the
surface
3. For isolating producing zones from
water-bearing zones (hydraulic bond)

7. CEMENT BOND LOG
(CBL)
Concept of CBL:

8. Transmitter sends acoustic wave to casing/cement and
then receivers receive acoustic signal that transfer
through casing to cement and reflects to receivers.
Acoustic wave at receivers is converted to amplitude
(mv).
Low amplitude represents good cement bond
between casing and hole; however, high amplitude
represents bad cement bond.
The concept likes when we knock pipe. If there is
something coverage around pipe, the reflection sound
will be attenuated, and vice versa.

10. CEMENT BOND LOG
(CBL)
What are we
looking for?

11. Minimum interval of continuous 60% bonded
cement in a continuous confining shale.
Rule-of-Thumb: < 10mV on amplitude curve
for x-amount of feet.
For heavier casings, can sometimes accept
< 12mV or < 13mV but this is fairly RARE.

12. CBL Interpretation Guide: