Broad-band acoustic low frequency collimated beam for ultrasonic imaging

Abstract

Ultrasonic and sonic imaging from a borehole is a widely used technique for hydrocarbon reservoir characterization. A typical acoustic transducer in a borehole can produce a narrow beam only at ultrasonic frequency hundreds of kHz or higher. On the other hand, high acoustic frequencies are rapidly attenuated in the formation and result in shallow penetration. To allow deeper penetration, low frequency operation is needed. We report on the development of a lower frequency broad band collimated and steerable acoustic beam source, which is sufficiently compact to fit inside a borehole and is capable of probing for rock information in the near-borehole environment. Some of the main advantages of the source presented in this study are related to: (1) the beam collimation for better spatial resolution, (2) beam steerability (360 degree in azimuth and inclination), (3) the broad-bandwidth (20–120 kHz) and (4) specific pulse shape for simpler signal processing and data analysis. Laboratory experimental data simulating open and cased wellbores will be presented.