TX 75083-3836 U.S.A., fax 01-972-952-9435. AbstractThe completions of ultra-deepwater wells in the Gulf of Mexico are requiring higher mud weights and heavier casing strings in order to economically maximize production rates and to control high-pressure reservoirs. Many operators are completing multiple wells using synthetic oil-based mud weights in excess of 15 lbm/gal, casing with a wall thickness of more than 0.625 in. and special cement materials. Standard cement bond logging tools, however, may not be well suited to evaluate the extreme casing conditions or analyze the casing/cement interface because of the acoustic properties of these materials.In order to obtain quality answers to the casing/cement evaluation questions, a study was performed to evaluate the results provided by sonic and ultrasonic tools in the different casing materials.The results were obtained from a combination of special small-scale experiments and field applications. This work provides the technical background for extending the ultrasonic measurements beyond normal industry conditions.The measurement resolution and limitations in these extreme conditions are also discussed. It was found that the latest generation of ultrasonic cement evaluation tools could provide high-quality measurements of the casing dimensions and the cement acoustic impedance properties when utilizing the proposed procedures. Field examples are presented to illustrate the actual application and the response of the ultrasonic tools to various extreme cement evaluation conditions.