钻柱信道内隔声体结构建模与仿真分析

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

在随钻声传输技术中自钻柱底部上行的井下噪声及回波干扰严重降低声信号接收性能.基于低频纵波在声阻抗突变处及周期性管结构信道内的传输特性,设计具有周期性凹槽的隔声体结构.结合信道内噪声特征及隔声阻带中心频率,比较分析单结构隔声体短节与组合结构隔声体频响特性及隔声量,并将隔声体引入钻柱信道,用钻柱内一维低频纵波传输有限差分算法,时、频域仿真分析隔声体在信道内的隔声性能.结果表明,组合隔声结构可实现较宽的隔声频带,使噪声水平降低20 ～40 dB,从而改善信噪比、提高传输速率,为钻柱声遥测系统优化设计提供方法基础.

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 telemewy systems.