尺寸差异钻杆组成的钻柱中声传播特性测试

Tests for acoustic propagation characteristics in drill string composed of size-difference drill pipes

随钻实测信息声波传输技术是井下信息无线传输技术领域的一个重要研究方向。作为信息传输通道的钻柱是由尺寸存在差异的钻杆相连接构成,钻杆的尺寸差异对钻柱中声的传播是否存在影响是声载波选取及检测必须要了解的问题之一。建立了用于测试钻柱中声波传播特性的试验装置,对不同类型钻杆组成的钻柱中声波的传播特性进行了测试;利用基于声透层理论建立的钻柱中声传播特性研究模型对测试结果进行了理论分析。研究结果表明:组成钻柱的钻杆存在尺寸差异时,钻柱中声波传播特性有所改变,表现在通带的个数减少,有些通带消失,且通带的宽度变窄;尺寸存在差异的钻杆组成的钻柱中声衰减比周期性钻杆要大;低频通带声波受钻杆尺寸差异影响相对较小;存在着个别的排列方式,可以减小钻杆尺寸差异的影响。基于声透层理论的钻柱中声传播特性研究模型在计算前4个通带时较为准确。

The acoustic transmission of information, measured by MWD, is an important research direction of underground information wireless transmission technology. The drill string serving as information transmission channel was composed of size-difference drill pipes, so it is important to understand the relationship between the drill pipe size- difference and acoustic wave propagation characteristics in the column. That is related to the selection of sound carrier and detection measure. A test device for testing the drill string acoustic propagation characteristics was established, and relecant tests were carried out. The test results were analysed by using the model of sound propagation based on the acoustic permeable layer theory. The results show that： with the application of size-difference drill, the acoustic wave propagation characteristics of drill string will be changed, bands reduces, some of the pass-bands disappear, and the which behaves in the following aspects; the number of pass- pass-band width is narrowed; when acoustic waves propagate through the drill string composed of size-difference drill pipes, the attenuation is bigger than that through the cyclical drill. Less affected by differences in the drill pipe sizes are the low-frequency pass band acoustic waves; there is some arrangement with which the effect can be reduced. In the information carrier selection and testing, the impact of channel structure should be fully considered. The theoretical model of acoustic propagation is exact in the calculation of the first 4 pass-bands.