随钻声波测井四极子发射换能器的设计

The design of quadrupole transmitting transducer used in LWD acoustic logging

随钻四极子发射换能器作为随钻声波仪器的核心部件,其工作性能直接影响随钻地层横波的测量效果。提出一种基于金属基片结构的随钻四极子发射换能器,其一阶弯曲模式可用于随钻四极子声源。利用有限元法对该换能器进行了设计分析,结果表明在5 kHz附近存在一阶弯曲振动模态,其径向位移值分布及发射电压响应均优于现用的瓦片状四极子换能器,非常适合随钻四极子工作频率及声场的测量需求。针对一阶弯曲振动模态,数值模拟了几何尺寸对金属基片结构的四极子换能器性能参数的影响。换能器谐振频率随着陶瓷片厚度、陶瓷片高度、陶瓷片张开角度、金属基片厚度的增大而升高。最大发射电压响应随陶瓷片高度、陶瓷片张开角、金属片厚度的增大而升高;随着陶瓷片厚度的增大先升高后逐渐降低。金属基片采用铝片可以使换能器有较大的发射功率。数值模拟结果可以对随钻声波测井仪四极子发射换能器的设计提供参考。

As the core component of logging while drilling(LWD)acoustic logging tool,performance of quadrupole transducer directly affects measurement accuracy of formation shear wave.This paper proposes a kind of LWD quadrupole transmitting transducer based on metal substrate structure,and its first longitudinal bending vibration mode can be used for the LWD quadrupole acoustic source.The finite element method is used to design and analyze the transducer.The results show that the resonance frequency of the first longitudinal bending vibration mode is about 5 kHz,and its radial displacement distribution and transmitting voltage response are better than existing arc-shaped piezoelectric vibrator.This transducer’s resonance frequency and acoustic field characteristic are suitable for the measurement requirements of LWD quadrupole acoustic logging.Aimed at this first mode,the influence of geometrical size on the performance parameters of the transducer is simulated numerically.The resonance frequency will rise as thickness,height,opening angle of ceramic plate,or thickness of metal substrate increases.The maximum transmitting voltage response will rise as height,opening angle of ceramic plate or thickness of metal substrate increases,and increase first and then decrease gradually with thickness of ceramic plate increases.Aluminum metal substrate can make transducer have higher transmitting power.The numerical simulation results play a good guiding role on design of the quadrupole transmitting transducer.