A technique to evaluate the cement bond quality through filtering the ultrasonic reflected wave

Cement bond quality is very important to keep an oil well from hydraulic communication between zones.In cement bond quality detection,the ultrasonic echo method is widely used for its capability of channeling azimuth detection.Because of the high acoustic impedance of the casing,the amplitude of the reflected wave outside the casing is small and cannot easily be used to evaluate the cementing job.The wave that can propagate into cement and formation through the casing concentrates closely on the casing resonant frequency.To reduce the amplitude of the reflected wave from casing inner surface and highlight the part of the reflected wave which carries cementing quality information,we filter the reflected full wave according to the casing resonant frequency.There are several wave packets in the filtered waveform.These wave packets are different for different cement conditions,so that the cement bond quality can be told from the differences.Reflection of an acoustic beam with finite width is modeled to reveal the sensitivity of the amplitude of the received ultrasonic reflected wave to the incident angle.