Visualization of Leaky Ultrasonic Lamb Wave Experiments in Multilayer Structures

Leaky ultrasonic Lamb waves propagating in liquid-filled steel pipes are widely used by the oilfield service industry in wellbores to measure the acoustic properties of the material located outside the pipe. Typically, the annular region between the steel pipe and the geological formation is cemented to provide mechanical integrity and to ensure hydraulic isolation between different geological layers in the well. We present results from an experimental study along spatial and temporal dimensions to visualize the propagating waveforms of such measurements for liquid or solid annular materialsbehind the steel pipe. Our measurements focus on the lowest-order flexural waves. These radiate energy into neighboring layers if the flexural phase speed is supersonic with respect to the bulk compressional- or shear-wave phase speeds of the adjacent media. In the case of a compressional phase speed higher than the flexural phase speed, the resulting flexural mode attenuation is then strongly reduced. Several annular materials with compressional velocities higher and lower than the flexural phase speed were investigated to demonstrate this effect. Finally, the propagation of compact flexural-wave packets along the steel pipe was recorded, and the results were compared with computed modal dispersion and attenuation curves.