The Research Of Lamb Waves In Layered Solid Plates At Oblique Incidence

Ultrasonic cement bond quality evaluation logging is one of the more widely used method that can effectively evaluate the quality of cementing.The Isolation Scanner(Schlumberger's new cementing quality assessment instrument)can accurately and effectively evaluate the quality of the cement bond by combining vertical incidence technique and ultrasonic oblique incidence method.Based on the working principle of the Isolation Scanner,This paper simplify the cased-hole model as the plane multilayer dielectric model,then simulated the wave ultrasonic oblique incidence from the fluid onto the interface of the Casing by using the two-dimensional rotated staggered grid finite difference method.Then analysised the relationship between the wave and the cement.We selected two incident angle: angle(38°)and angle(38°),when esearching ultrasonic oblique incidence.The numerical simulation results show that: A0 mode Lamb wave,S0 mode Lamb wave and Stoneley wave can be excited in the casing by using two angle oblique incidence;When using the angle(18°)oblique incidence,the S0 mode wave amplitude is smaller than A0 mode wave amplitude;When using the angle(38°)oblique incidence,the A0 mode wave amplitude is much smaller than the amplitude of the S0 mode wave;The sound attenuation coefficient of S0 mode wave increases with the increasing of the acoustic impedance of cement.The sound attenuation coefficient of A0 mode wave increases with the reducing of the acoustic impedance of cement.In summary,we use the sound attenuation coefficient of A0 and S0 to evaluate the quality of the cement bond.