Quantitative criteria for predicting by the use of the cement bond log whether interzone fluid communication will take place through the casing-formation annulus are derived for cementing and logging conditions on the Cedar Creek Anticline. These criteria consist of a critical amplitude above which combination will take place and critical interzone distance below which communication will take place. These criteria were derived by correlation in 28 wells of conclusive communication tests with cement bond logs which meet certain quality control and calibration requirements. It is found that adequate control of the cement bond logs for quantitative application is dependent on four factors:
Acoustic properties of fluid in the casing,
Satisfactory repeatability,
Satisfactory centralization, and
Appropriate response in unbonded casing and in unbonded casing collars.
In this study, adequate calibration was obtained by requiring specified responses of the CBL in unbonded casing and in unbonded casing collars and by comparing the logs from the different available systems in a common test hole. It is shown that other phenomena which significantly affect CBL response but which are not associated with log quality control or with the presence and strength of the cement in the annulus are "early arrivals" opposite high velocity formations, the apparent presence of a "micro-annulus" between casing and cement sheath, and a change in apparent bonding with time when gilsonite cement was used. The significance of the micro-annulus to interzone communication has not been established and is still under study.
