Experiments were conducted to study how sonic and ultrasonic cementation logs are affected by microannuii. By creating both gas- and liquid-filled microannuii of known sizes at the casing-to-cement interface, measurements could be recorded and analyzed.

Depending on the nature of the fluid and the size of the microannulus, results showed that all cementation logs were sensitive to microannuii. Gas at the casing-to-cement interface had a very strong effect on the ultrasonic measurement but had minimal effect on traditional sonic Cement Bond Log (CBL) measurement if the microannulus was in the range of one μm. CBL measurement was very sensitive to water-filled microannuii. Ultrasonic measurements were capable of evaluating the quality of the cement behind a water-filled microannuii as large as 100 μm. Liquid-filled microannuii could be identified through the large coupling attenuation measured with multi-spacing sonic tools.

Analysis of these experiments brings new insights to cementation-log interpretation.

You can access this article if you purchase or spend a download.