Mapping of ultrasonic Lamb-wave field in elastic layered structures using laser probes

Abstract

In the oil and gas industry, the nondestructive evaluation of cemented steel pipes in subterranean wells commonly involves the use of ultrasonic guided Lamb waves. These measurements help determine whether the cement annulus between the rock formation and the steel pipes provides hydraulic isolation between the different depth zones of the well. Such techniques employ the excitation of leaky flexural and extensional waves inside the highly contrasting steel layer to distinguish solids from liquids in the inaccessible region outside the pipe. Furthermore, the annular cement layer may exhibit defects such as cracks or channels that may compromise zonal isolation. We present laboratory measurements using laser interferometry and comparative modeling results along spatial and temporal dimensions to visualize and quantify the propagation of leaky Lamb waves for a variety of homogeneous liquid and solid layers behind a steel sheet in planar and cylindrical geometries. We characterize annular materials with different compressional velocities to demonstrate the effect on mode dispersion and attenuation. Furthermore, we study the effects on transmission and reflection of Lamb waves at discontinuities such as conduits in the inaccessible layer.