Mapping of ultrasonic Lamb-wave field in elastic, layered structures using acoustic and 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 ensure that the cement annulus between the rock formation and the steel pipes provide hydraulic isolation between 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 which may compromise zonal isolation. We present laboratory measurements using piezo-electric needle probes and laser interferometry, as well as comparative modeling results along spatial and temporal dimensions to visualize and quantify leaky-Lamb-wave propagation for a variety of homogeneous liquid and solid layers behind a steel sheet in planar and cylindrical geometries. We characterize several annular materials with compressional velocities, which are higher or lower than the Lamb phase speed 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.