Methods to evaluate conventional cements with logging data may not yield valid results in foamed cements. Logging tools commonly used in cement evaluation are the traditional cement bond log (CBL) tools and the modern ultrasonic scanning tools. CBL tools provide waveform images and acoustic amplitudes that together help describe cement-to-pipe and cement-to-formation bonding. Ultrasonic scanning tools contribute circumferential images and detailed information regarding the cement-to-pipe bond. The major problem in evaluating foamed cements is that their impedance values can be below that of annular fluids, such as mud or water. Thus, a standard interpretation of ultrasonic images and data in foamed cements may provide an incorrect diagnosis of the cement bond and could lead to unnecessary remedial cementing activities.
A new interpretation method expands and improves on previously published methods to effectively evaluate foamed cements with the common cement-evaluation tools. This method uses ultrasonic scanning data to provide detailed information regarding the cement-to-pipe bond and allows foamed cement to be distinguished from mud or spacer fluid behind casing. Cement-slurry weight and composition do not affect this technique. The technique does not require additional logging tools or passes and thus does not introduce additional logging or rig expenses.
Examples are presented showing that the new method is valid and is effective in both time and cost. These examples will illustrate several new ultrasonic cement-bond curves that were developed as a result of the new method and that, when used in conjunction with CBL amplitude data, improve foamed-cement evaluation. In the examples, the interpretation is focused to answer the basic question, "Should remedial cementing be performed, or should the well be perforated for production?"