Modeling and simulation analysis for an acoustic isolation structure in a drillstring channel

Aiming at the reduction of a sound signal's transmission performance caused by uplink downhole noises and their echoes generated in the bottom of a drillstring while drilling, based on the transmission characteristics of low-frequency acoustic waves in mismatched acoustic impedances and a periodic pipe structure transmission channel, an acoustic isolation structure with a periodic groove structure was designed here. According to the noise features and the central frequency of acoustic isolation stopband in a drillstring channel, the frequency response features and sound reduction indexes for a single acoustic isolator and a combined acoustic isolator were compared. Then, the two acoustic isolation structures were induced into the drillstring channel. By applying a finite-difference algorithm for the one-dimensional propagation of longitudinal waves along the drill string, the acoustic isolation performances of the two acoustic isolators in the drillstring channel were analyzed with time domain and frequency domain simulations. The simulation results showed that the combined acoustic isolator can achieve a wider acoustic isolation frequency bandwidth with a 20~40 dB reduction of noise, and lead to the improvement of signal-to-noise ratio and the increase in transmission rate, the results provide a methodological foundation for optimal design of acoustic telemetry systems.