A Systematic Approach to Interpreting Cement Bond Logs

Abstract To achieve a more consistent and disciplined approach, and to achieve a higher rate of accurate conclusions, a cement bond log interpretation method has been organized and applied to hundreds of operations around the world. This method approaches the bond log from a "cementing perspective" and when applied to previously interpreted logs, resulted in an accuracy increase from approximately 30 % to greater than 90 %. This study of three-hundred and twenty five wells also showed that the most common error was the misinterpretation of logs for wellbore sections containing a microannulus. This paper details a five-step process, including an example of the numerous observations and decisions that are typically made, and introduces forty-three wellbore effects that may be key to accurate bond log interpretation. Besides accuracy, the vast majority of cement bond logs have been "under-interpreted," lacking important details. This new integrated approach to bond log interpretation is designed to provide a full interpretation, hence the zonal isolation summary, the nature and cause of any cement defects, and recommendations for remediation or future improvements, are all key parts of the final interpretation.