It is a promising measure to transmit downhole information by acoustic wave through drill string. However, the transmission distance and quality of acoustic signals in field conditions are still not satisfied because the acoustic frequency spectrum in drill string is vulnerable to interference. This paper studied acoustic frequency spectrum characteristics in periodic drill string by experiments under different axial tensile forces. The multilevel method is established to evaluate frequency spectrum through drill string based on improved radar chart. The impact of axial tensile force on spectrum characteristics is analyzed by the proposed method. The results indicate that the axial tensile force has remarkable impact on the acoustic frequency spectrum and passband characteristics. The spectrum characteristics change with axial tensile force. These changes are reflected in the position, width, and attenuation of different passbands. And the extent of changes is distinct to different passbands. Both the evaluation indicators of each passband and spectrum are change with increasing axial tensile force. The spectrum quality is excellent in the range of 17‐134 MPa for axial tensile force in drill string. And when the force exceeds 152 MPa, methods such as adjusting the carrier frequency and relay installation location are necessary to improve the transmission quality of acoustic signals.

中文翻译：

---

张力下周期性钻柱的声学频谱特性

通过声波通过钻柱传输井下信息是一种很有前途的措施。但是，由于钻柱中的声频谱容易受到干扰，因此仍不能满足现场条件下的声信号的传输距离和质量。本文通过不同轴向拉力的实验研究了周期性钻柱的声频谱特性。建立了基于改进雷达图的钻柱频谱评估方法。提出的方法分析了轴向拉力对光谱特性的影响。结果表明，轴向拉力对声频谱和通带特性有显着影响。光谱特性随轴向张力而变化。这些变化反映在不同通带的位置，宽度和衰减中。变化的程度对于不同的通带是不同的。每个通带和频谱的评估指标都随轴向拉力的增加而变化。钻柱轴向拉伸力的光谱质量在17-134 MPa范围内极佳。而且，当力超过152 MPa时，必须采用诸如调整载波频率和继电器安装位置的方法来改善声信号的传输质量。钻柱轴向拉伸力的光谱质量在17-134 MPa范围内极佳。而且，当力超过152 MPa时，必须采用诸如调整载波频率和继电器安装位置的方法来改善声信号的传输质量。钻柱轴向拉伸力的光谱质量在17-134 MPa范围内极佳。而且，当力超过152 MPa时，必须采用诸如调整载波频率和继电器安装位置的方法来改善声信号的传输质量。