Study on Experiment of Acoustic Transmission in Pipe String

As a feasible option, surface signals can be transmitted downhole by taking downhole oil pipe as channel and sound waves as medium. In this paper, a longitudinal wave transmission experiment is conducted for oil pipes with limited length, and experimental environment and equipment are prepared. The experimental objects include 10 oil pipes of three sizes, and each pipe is arranged with a set of velocity sensor. The experiments of impact signals and continuous sine signals are performed, revealing the time-domain and frequency-domain properties of sound waves during transmission through different pipe nodes. Through detailed analysis of the experimental results, it is concluded that spectral distribution of longitudinal wave in pipes presents a comb filter structure with alternating passband and stopband, which is validated in respect of frequency domain and time domain. Moreover, distortion and attenuation of longitudinal wave signals may occur within passband frequencies.