气体钻井钻柱拉应力对纵波特性的影响

The Effect of Tensile Stress on Longitudinal Wave Characteristics of Drill String for Gas Drilling

为分析气体钻井钻柱中拉应力对纵波传播特性的影响,提升声信号传输质量及距离,采用声弹理论建立了应力-纵波波速分析模型,对波速随拉应力的变化规律进行了分析,并利用研制的试验装置测试了纵波波速及频谱特性随拉应力的变化规律。研究结果表明:拉应力是钻柱中纵波特性的重要限制因素,波速随拉应力增加呈线性减小,实际钻柱中的声-应力系数需进行标定;随拉应力增大,频谱低频与中频段表现出通带发生偏移、带宽变窄、幅值降低及衰减为阻带的不利变化,高频段通阻带特性相互转变尤为明显。所得结果可用来指导气体钻井钻柱中声载波参数优选及系统结构设计,从而降低拉应力对钻柱中声信号的不利影响。

To analyze the influence of tensile stress of drill string on the propagation characteristics of longitudinal waves during gas drilling,and to improve the quality and distance of acoustic signal transmission,a stress-longitudinal wave velocity analysis model is established using acoustic elastic theory.The law of wave velocity changes with tensile stress is analyzed.The developed test device is used to test the changes of longitudinal wave velocity and frequency spectrum characteristics with tensile stress.The research results show that tensile stress is an important limiting factor for longitudinal wave characteristics in drill string.The wave velocity decreases linearly with the increase of tensile stress.The acoustic-stress coefficient in the actual drill string needs to be calibrated.With the increase of tensile stress,the low and middle frequency spectrum shows a shifted passband,narrowed bandwidth,reduced amplitude,and amplitude attenuation to unfavorable stopband.The interconversion of high frequency pass and stop band characteristics are particularly obvious.The results obtained can be used to guide the selection of acoustic carrier parameters and system structure design of drill string for gas drilling,thereby reducing the adverse effects of tensile stress on acoustic signals on the drill string.