Professional Use of Borehole Geophysical Logging for Cement Bond Quality Evaluation in Gas Production Wells, Offshore Nigeria

Wellbore integrity in offshore gas production wells depends critically on the quality of cement placement in the annular space between the casing and formation, and inadequate cement bonding represents one of the most significant sources of sustained annular casing pressure and well barrier failure in Nigerian deepwater operations. This professional study evaluates the application of acoustic cement bond logging and ultrasonic imaging tools for cement quality assessment in six gas production wells in a deepwater block offshore Nigeria. Cement bond logs, including conventional bond logs and variable density logs, were acquired in all six wells. Ultrasonic cement mapping using the PulsEcho tool was also acquired in three wells to provide azimuthal coverage. Log interpretation followed the API recommended practice for evaluating cement bond quality, with acoustic impedance values derived from ultrasonic measurements providing quantitative cement fill assessment. Results indicate that five of the six wells have segments of microannulus or partial channelling identified in the upper cemented sections, with one well showing a continuous gas migration pathway identified by elevated free-pipe amplitude responses over a 45-metre interval. A remedial squeeze cementing programme was designed using the log-identified channel positions as injection targets. Post-squeeze logs confirm channel isolation in four of five treated intervals. The study develops a cement quality evaluation workflow incorporating both acoustic and ultrasonic data types that reduces interpretation subjectivity and improves remediation planning efficiency. Keywords: cement bond log, borehole logging, gas wells, wellbore integrity, offshore Nigeria