Question

Which of the following logging methods is/are NOT used for investigation in Cement Bond Logging (CBL)?

• A. Gamma ray
• B. Neutron
• C. Electrical
• D. Acoustic wave

Hint:

Recall that CBL is fundamentally an acoustic or sonic measurement; the other listed logs are open hole or correlation tools only.

Answer 1

The Correct Option is A, B, C

Step 1: Understand the purpose of Cement Bond Logging (CBL):
Cement Bond Logging is carried out after a well has been cased and cemented, to check the quality of the cement bond between the casing and the formation. It is fundamentally an acoustic (sonic) logging technique: a transmitter sends a sound pulse into the casing and a receiver measures the amplitude of the received signal along with its travel time. A strong bond between casing, cement and formation attenuates the sound wave, while a poor bond, such as one with fluid or gas channels, allows the signal to travel with much less attenuation. This acoustic wave measurement is the actual physical basis of cement bond investigation.
Step 2: Identify the single tool actually used for CBL investigation:
Because CBL evaluation depends entirely on how the casing and cement attenuate an acoustic pulse, the only logging method genuinely used to investigate the cement bond is the acoustic or sonic wave tool. No other logging physics gives information about the mechanical bonding condition of cement behind a steel casing.
Step 3: Identify why gamma ray is NOT part of the bond investigation:
A gamma ray curve happens to be run alongside the CBL tool string, but only as a depth correlation reference against the open hole gamma ray log and to help tie the log to the casing collar locator signal. It measures natural formation radioactivity, which has nothing to do with cement bonding, so it does not investigate the cement bond itself even though it accompanies the CBL run.
Step 4: Identify why neutron and electrical logs are NOT part of the bond investigation:
Neutron logging tools measure the hydrogen index of the formation and are used for open hole porosity evaluation; they play no part in a cement bond investigation. Electrical or resistivity logging tools measure formation resistivity to identify hydrocarbon versus water bearing zones in an open hole; they also have no role in evaluating the cement bond behind casing, since resistivity measurements are not meaningful for assessing the bonding of cement to steel casing.
Step 5: Conclusion:
Gamma ray, Neutron and Electrical logging are all open hole or correlation tools that are NOT used to investigate the cement bond itself, while Acoustic wave logging is the actual method used for CBL investigation.
Final Answer:
\[ \boxed{\text{Gamma ray, Neutron and Electrical logging (Options A, B and C)}} \]