Acoustic frequency selection in acoustic logging tools

Abstract

A logging system has a sonde in a borehole, which transmits sonic waves with one or more dipole sources to optimally excite dipole flexural mode sonic waves in the borehole. The system first determines the Airy frequency of the borehole. Then, the dipole sources are fired at a dipole firing frequency selected based on the Airy frequency.

Description

technical field [0001] This invention relates to methods for characterizing the physical properties of subterranean formations by emitting acoustic waves in a borehole and processing the resulting acoustic waveform data, and in particular to optimal excitation of dipole bending in the borehole by selecting the acoustic frequency at which the acoustic waves are emitted method of sound waves. Background technique [0002] In the production of natural hydrocarbon (eg, oil) formations, wellbores are generally drilled from surface locations into the subsurface. Measurements of various phenomena and properties downhole are typically performed to determine various properties related to subsurface resources or formations or other properties related to wellbore treatment. To make such measurements, various borehole sensors or detectors may be placed in the drill bit, in the bottom hole (or borehole) assembly (BHA), in the drill string above the downhole motor, or below the surface ...

AI Technical Summary

Problems solved by technology

However, this approach requires a detection system with a larger (and thus more expensive and complex) dynamic range and higher power consumption in generating such a wide frequency band of signals

Since utility logging tools have power-limited transmitters and limited-dynamic-range receivers, they cannot transmit sufficient power and broadband signals, but only use a narrow frequency range

However, in this case, if the wrong excitation pulse frequency is used for a given borehole and structural feature, no useful signal can be obtained over a sufficient frequency band

Another problem with using a broadband dipole source is that the resulting audio waveform can contain undesired patterns such as dipole-squeezed waveforms

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