1980. Society of Petrophysicists & Well Log Analysts
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ABSTRACT Since the introduction of Cement Bond Logging (CBL) in the mid- 1950''s, much has been learned about the factors affecting interpretation of logging data. From past experience, logging data may not always be representative of the actual cement-to-casing bond. In fact, improper logging and/or cementing techniques have frequently resulted in misleading cement bond interpretations resulting in unnecessary squeezing or completions having annular communication. Various procedures can be used to ensure that meaningful cement bond information is obtained. The most critical for the operator is to use cementing techniques that minimize the formation ofmicro-separation between the casing and the cured cement. Since these separations impede the acoustic coupling between casing and cement, the recorded casing signal is not representative of the integrity of the cement job. The CBL recording exhibits a unique response to micro-separations, and when they are noted the logging environment must be changed to obtain representative data. The transmitter-receiver configuration and spacing are also important -- both for defining cementbond quality and for ascertaining measurement validity. For example, the casing signal amplituderesolution in bonded casing is determined by transmitter-receiver spacing: a short spacing provides better resolution. Also, a single receiver transit time measurement can provide quality control by indicating when, or whether, recorded amplitude signal is truly representative of casing-to-cement bond conditions. Tool design is, therefore, critical. By controlling these factors and utilizing interpretation techniques that consider all the cement and casing variables, the operator can monitor and improve primary cementing and squeezing operations.
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