Cement Bond Log Guide For Cementing Evaluation
https://youtu.be/i6k8ViHvG0Q

A cement bond log (CBL) measures the amplitude or attenuation of waves propagating axially along with a casing. The attenuation of the wave depends upon the materials on both sides of the casing: mud inside the casing and cement in the annular space. The effect is more pronounced on the casing-cement interface than on the mud-casing interface. The amplitude of the first arrival wave at the receiver indicates the presence of cement around the casing.
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