Method for evaluating the quality of cement surrounding the casing of a borehole

摘要

A method for evaluating the quality of the cement surrounding a borehole casing is provided. The method generally comprises obtaining signals which were recorded by a CET tool known in the art, and processing the signals by: dividing each signal into particularly defined time windows; determining absolute magnitudes for each signal which are functions of the energy of the signal in the respective windows; determining normalized magnitudes for each signal from the absolute magnitudes and normalization parameters; and evaluating the quality of cementation as a function of the fact that the normalized magnitudes for each signal obey a predetermined law, and as a function of the relationship between each normalized magnitude and a pair of threshold values respectively associated therewith. According to another aspect of the invention, information obtained from a CBL tool known in the art is compared to the information gained from the CET tool. If the curves output by the respective tools diverge, the presence of gassy cement is determined. If, after correcting for gassy cement the curves diverge, additional information as to the environment beyond the casing may be obtained.