Cement Bond Log Mean?
A cement bond log (CBL) is a means to determine the integrity and quality of a cement bond. After a borehole is drilled, the casing is lowered and cement slurry is injected into the annulus between the casing and the borehole wall. The cementing is done to ensure that the casing is well supported and fluid is prevented from finding it way to the surface. Cementing is also done for other purposes such as zonal isolation and creating a hydraulic seal.
Centralizers are used to ensure that the casing is centered in the borehole and does not lean against the borehole wall.
Trenchlesspedia Explains Cement Bond Log
A cement bond log measures the integrity of the cement bond and is obtained using sonic tools which measure the amplitude of sound pulses from the transmitter to the receiver. The acoustic signal travels down the casing wall in between a transmitter and receiver. The maximum amplitude can be observed in unsupported pipe and is least in a casing that has been cemented well. The wave train of amplification is displayed as a variable density log (VDL) with positive and negative waves.
A cement bond log works on the principle that in the presence of cement, the acoustic signal is more attenuated than when no cement is present.