The Cement Bond Tool

The present Cement Bond Log (CBL) provides a measurement of the compressive strength of the cement layer between the casing and the borehole walls. It also gives a qualitative estimate of the cement to formation bond. The Cement Bond Tool (CBT) has been developed specifically to evaluate cemented casings while eliminating the deficiencies of the standard CBL tool: sensitivity to tool centering, fluid attenuation, receiver sensitivity, temperature drifts and calibration. The CBT tool is a 2 3/4" sonic tool which provides a BHC ratio attenuation measurement with two receivers symmetrically located between an upper and a lower transmitter. The measurement is self-calibrating, and is not affected by mud attenuation, temperature effects, and eccentering (up to 0.3"). In addition to attenuation, it records an amplitude CBL log for transmitter-receiver separations of .8", 2.4", and 3.4". The 0.8" separation is used when logging in fast formations; its use is limited to casings smaller than 7". The 2.4" separation provides an amplitude log similar to the current 3" CBL with an improved signal-to-noise ratio.