Abstract

A new technique for evaluating both the strength and distribution of cement behind casing has been successfully developed and operated in Indonesia. This new method overcomes the limitation of conventional cement bond logging systems by providing 8 directional measurements of the bond quality around the casing.

Small radial segments of the casing are stimulated in thickness resonance with an ultrasonic pulse from each of 8 transducers. The casing reverberates and the rate of decay of the reverberation as measured by each transducer can be related to the quality of the cement behind the casing. By appropriate choice of operating frequency it is possible to minimize the effect of micro-annulus. Additional analysis of the reverberation decay allows the detection of outer casing strings, fast formation arrivals and gas in the annulus.

A direct, visual, presentation of the cement quality along 8 sections of the casing allows for a rapid identification of channeling and good cement bonding without ambiguity.

In addition the technique can provide extremely precise indications of casing internal diameter and distortion along 8 radii.

A description of the tool principle and a selection of example results from Indonesia are presented and discussed to demonstrate the wide applications of the technique.