钻柱结构声传输特性试验研究

声传输方式因结构简单、成本较低、易于定向发射等优点成为研究的热点。为寻求更高数据传输速率和受工作环境影响更小的井下随钻无线传输技术，设计了近钻头声信号传输试验系统，论述了声传输的信道特性、影响因素和信号检测方法，分析了管箍界面以及泥浆介质的阻尼影响，通过色散曲线对钻杆中纵波传输的频域特性进行了详细分析，试验研究了近钻头中声信号传输时激励信号与接收信号的关系。结果表明，周期性钻柱结构具有复杂的声特性，在钻柱信道中，通带和阻带交替出现，且在一个频带周期内随着频率的增加，通带先变窄再变宽，阻带则先变宽再变窄。存在适合高速和大信息量传输数据的声信号频带和信号特征。

Acoustical Properties Experimental Study within Drill Strings

The technology of downhole acoustic telemetry has become research central issue because it has advantages of simple structure and low cost and so on. In order to obtain higher data transmitting rate and the wireless transmitting technology while drilling with less influence by working condition, the system of near bit acoustic signal transmission was designed. Acoustical properties of drill strings and influencing factors and checking ways were discussed. Influence of discontinuous boundaries on transient acoustical behavior of periodic drill pipes was analyzed. The attention was also given to effect of mud. Frequency-domain analysis was made using the dis- persion curves. The relations of the input signal to the receive signal within the drill string were studied. The results showed that drill string as a periodic structure has complex acoustical properties in time and frequency domains. The pass bands and stop bands present themselves alternately in this acoustical channel of drill strings. With the increase of frequency, the pass bands firstly narrow and then widen, and the stop bands firstly widen and then narrow in one frequency band. The results indicated the existence of frequency bands and signal characteristics which were virtually free of attenuation and suitable for data transmission at high bit rates.