一种新型井下声波发生装置及其声波传播特性

井下有限空间内声波的有效发生与声能量的高效传递是声波在钻柱中稳定、长距离传输的前提,高效可靠的发生装置是实现井下信息声波传输技术现场化应用的关键。为了实现速度快、准确性高、抗外界因素干扰能力强的井下信息传输,基于超磁致伸缩换能器设计加工了一种井下声波发生装置,并通过建立试验系统,对该装置的功能性及关键参数设计开展了研究。研究结果表明:①带内孔的单级圆锥变幅杆是辐射声波首选,换能器在圆锥变幅杆小端激励的声波辐射进入钻柱中能够获得平面波;②在变幅杆放大系数极小值点附近设计长径比能够有效提高低频段声波能量传递效率;③黄铜材料的声传递介质具有较高的滤波质量与声能量传递效率;④声波能量传递效率随换能器预紧力增加,先增加后保持不变,7.20 kN预紧力能够获得最佳传递效率。结论认为,在井下声波发生与中继装置的设计过程中,应充分考虑换能器声波辐射方式与结构参数对声波能量传递效率的影响;建议进一步研究声发射端机械结构、声载波参数等因素对钻柱中声传播特性的影响,以加快井下信息声传输技术现场应用的步伐。

A new downhole acoustic wave generator and its acoustic propagation characteristics

Effective generation of acoustic waves and efficient transmission of acoustic energy in the limited downhole space are prerequisites for the long-distance stable transmission of acoustic waves in drill strings, so an efficient and reliable generator is the key to the field application of downhole acoustic signal transmission technology. In order to realize the downhole information transmission of high speed, high accuracy and strong external factor immunity, we designed a downhole acoustic generator and it was manufactured based on the giant magnetostrictive transducer. Then, an experimental system was built up to study its functions and key parameters. And the following research results were obtained. First, a single-stage conical horn with an inner hole is the first choice for acoustic radiation, and the plane waves can be obtained by the transducer when the acoustic wave radiation enters the drill string from the small end of the conical horn. Second, the energy transfer efficiency of low frequency acoustic waves can be effectively improved when the horn length-diameter radio is designed near the minimum amplification coefficient point. Third, acoustic transfer medium made of copper has a higher filtering quality and transfer efficiency of acoustic energy. Fourth, the transfer efficiency of acoustic wave increases first and then remains unchanged with the increase of transducer pre-tightening force, and the optimal value is obtained at the pre-tightening force of 7.20 kN. In conclusion, the impact of transducer's acoustic radiation mode and structural parameters on the transfer efficiency of acoustic energy shall be fully considered during the design of the downhole acoustic generating and relaying device. And it is recommended to research further the effects of the mechanical structure of the acoustic emission end and the acoustic carrier parameters on the acoustic propagation characteristics in drill strings so as to speed up the field application of downhole acoustic signal transmission technology.