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] The present invention relates to a method of characterizing the physical properties of subsurface formations by transmitting acoustic waves in a borehole and processing the resulting acoustic waveform data, and in particular to optimal excitation of dipole bending in a wellbore by selecting the acoustic frequency of the transmitted acoustic waves sonic method. Background technique [0002] In the production of natural hydrocarbon (eg, oil) formations, wellbores are typically drilled into the subsurface from a surface location. Measurements of various phenomena and properties downhole are typically performed to determine various properties associated with subsurface resources or formations or other properties associated with wellbore treatment. To make such measurements, various wellbore sensors or detectors can be placed in the drill bit, in the bottom hole (or wellbore) assembly (BHA), in the drill string above the downhole motor, or below the surfac...

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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