Assessment of Reliability of Cement Bond Evaluation with Some Interesting Field Case Studies

Abstract

Abstract High numbers of lack of hydraulic zonal isolation and occurrences of numerous high annulus pressure problems in wells in Middle East which has led to more remedial cementing and also workover rig days, has encouraged the industry to consider more efficient cement bond evaluation methods and discriminate between zonal isolation and cement bond log interpretation. Therefore, in this paper the effects of the important parameters on cement bond logs including casing size, well deviation, type of fluid, and mud weight during the logging operations, surface applied pressure and microannulus, fast formations, type of formation, tool eccentricity, casing eccentricity, multiple casings, pressure and temperature, effect of cementing operations have been considered and the cement bond reliability has been discussed. In this study, by presenting interesting examples of different cement bond logs, a comprehensive assessment of different cement bond log evaluation methods (conventional CBL/VDL, Radial CBL/VDL, Ultrasonic logs like segmented bond logs, isolation scanner in multiple casing scenario) have been performed which shows sonic cement bond logs are under some reliability risks and may not be always descriptive of zonal isolation. As ultrasonic tools outperform sonic ones, they are suggested specially wells with special cases.