Cement bond log

What is it?

CEMENT BOND LOG (CBL)

A cement bond log (CBL) is a type of log thatmeasures the loss of acoustic energy as itpasses 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.

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.


What is it used for?

Cement bond logs are used to detect thepresence or absence of external cementbehind 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 surface3. For isolating producing zones from water-bearing zones (hydraulic bond)


Concept of CBL:

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.


What are welooking for?

Minimum interval of continuous 60% bondedcement in a continuous confining shale.

Rule-of-Thumb: < 10mV on amplitude curvefor x-amount of feet.

For heavier casings, can sometimes accept< 12mV or < 13mV but this is fairly RARE.

CBL Interpretation Guide:

Cement bond log

Science