January 2013
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Ultrasonic Lamb wave measurement method based on oblique incidence can solve some difficult problems, such as low density cement evaluation or II interface cement bonding quality. Lamb wave propagation in multilayer medium in casing well is studied by using the finite element method in this paper. Acoustic field and received waveforms are simulated when Lamb wave propagates in different annulus materials. Results indicate that when ultrasonic wave is incident upon interface of liquid and casing, it propagates along the interface while leaking energy into the liquid and cement. And it forms leaky Lamb wave which consists of strong energy AO Lamb mode and weak energy SO Lamb mode. When AO Lamb mode propagates along the casing well, only shear wave is excited and measured in fast cement, however, both shear wave and compression wave are excited in slow cement. Therefore, the thickness of cement sheath or second interface cement bonding quality can be detected according to the reflection wave from interface of cement sheath and formation.