Amplitude features of formation wave in acoustic full waveform of casing wells
套管井声波全波列中地层波的幅度特性

We utilize formation wave of acoustic full waveform in casing wells to detect cementing quality of the secondary interface. Except for formation attenuation and casing wave disturb, the formation wave is mainly influenced by acoustic impedance gradient of the secondary interface. Hence, based on acoustic potential function and boundary condition on solid interface, we get reflection coefficient and refraction coefficient of longitudinal wave and transverse wave on solid-solid interface, and provide approximate formula of the reflection coefficient and the refraction coefficient about the first critical angle of incidence. We analyze relation between the refraction coefficient and acoustic impedance. Numerical results show that the amplitude value of the formation wave reduces with increasing acoustic impedance gradients of the secondary interface. The relation is nonlinear. After attenuation correcting and disturb correcting, we reprocess the formation wave by acoustic impedance correcting based on refraction coefficient of critical incidence in order to eliminate formation acoustic impedance factor of influencing the formation wave. In field data processing, we utilize the formation wave amplitude to estimate cementing quality of the secondary interface, and gain good results.