Propagation Measurements for Acoustic Downhole Telemetry Systems
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AbstractAdvanced downhole communication technologies are used by well operators to monitor flow rate, temperature, and pressure data. Currently, the use of wired tools is popular although these tools present cost, maintenance, and reliability issues. Acoustic waves that propagate by vibrating the pipe's body inside the well are investigated as an alternative solution. While this technology offers great benefits, its propagation aspects inside the wells are unclear.This work explores the use of acoustic waves for downhole telemetry systems. A testbed was designed to investigate the propagation of acoustic waves over production pipes. The testbed comprises an acoustic tool that transmits data from inside wellbore to the surface without cables, an internally-developed receiver unit, and five segments of 7-inch production tubing that form a pipe string. Acoustic waves propagate by vibrating the pipe's body in this setup. Input frequencies from 100 Hz to 2000 Hz were investigated, and propagation measurements were taken along the pipe string. Further, the application of signal processing techniques is investigated to address the effects of dispersion and attenuation in the acoustic channel.Results of this work show that many harmonics propagate through the pipe string. Acoustic waves experience a frequency-dependent attenuation over the pipe string. Multipath reflections in the pipe string also cause noticeable signal dispersion. This work also shows that acoustic waves experience an extra frequency-dependent attenuation due to the presence of concrete; many high-order harmonics are heavily attenuated after encasing the pipe in concrete. Moreover, signal processing algorithms provide pronounced results in reducing the channel attenuation and dispersion. This work recommends that acoustic-wave technology is a promising cost-effective and reliable solution for wireless downhole telemetry systems. Furthermore, signal processing algorithms can be useful tools for the acoustic downhole communication systems.Technical contributions include: characterizing the channel response to different input frequencies along the pipe string; investigating the power spectral density, signal-to-noise ratio, and attenuation rate measures; studying the dispersion parameters of the channel; characterizing the effect of concrete on acoustic wave propagation; and applying signal processing algorithms.
