The Cement Bond Log (CBL) gives a continous measurement of the amplitude of sound pulses from a transmitter to receiver. This amplitude is maximum in unsupported pipe and minimum in well-cemented casing. The wave train can be displayed as a Variable Density Log (VDL) where the positive and negative cycles of the wave train are shaded black and white respecticvely.

CEMENT BOND LOG INTERPERTATION MODELS:

· “Amplitude” low. 
· “VDL” formation signals are strong. 
· Good cement. No need for squeeze

· “Amplitude” High. 
· “VDL” straight. No formation signals. "V" type Chevron patterns are seen at collars. 
· Squeeze cement needed.

· “Amplitude” is low and moderate. 
· “VDL” can shows both wiggly formation signals and straight casing signals 
· Squeeze can be necessary if the channel is long enough..

 *** 
4) MICROANNULUS (micro gap between cement and casing)

· “Amplitude” is moderate.. 
· “VDL” can shows both wiggly formation signals and straight casing signals 
·In case of doubt, repeat the log under 1000psi pressure to the well. The gap will be closed and log will change to "Good Cement"
· No need for squeeze..

*** 
 5) CEMENT WITHOUT BOND TO FORMATION

· “Amplitude” low. 
· “VDL” doesn't show casing and formation signals. Thin mud signals are visible 
· Squeeze needed 

Note: Keep in mind that gas in formation can give the same model. 

*** 
  6) CEMENT BOND IN HARD FORMATIONS 

· “Amplitude changes between low and high 
· Formation signals cover casing signals. 
· No need for cement...

---

CEMENT BOND WITH ACOUSTIC IMAGING
There are two types of cement bond evaluation tools :Sonic tools (as above) and ultrasonic tools (as below)