Acoustic transmission along the drill string for measurement while drilling (MWD) is an effective solution to the problem of the low transmission rate that results from mud pulse transmission. However, the actual downhole acoustic waves are affected by many factors, such as drilling fluid properties and, formation boundaries, and their effects on acoustic wave transmission in drill string are not thoroughly understood. To solve this problem, a longitudinal vibration model was proposed for acoustic wave propagation in drill string, and the coupling effect of the viscous damping of drilling fluid and the contact between the drill bit and formation was taken into account. The finite difference method with second-order accuracy is used to solve the mathematical model. The results show that an increase in drilling fluid damping causes the amplitude of the acoustic wave to decrease linearly, but the effect is not significant. The formation boundary mainly affects the low-frequency response of the drill string channel, while having little impact on the high-frequency response. Based on the above analysis, this paper proposes adding an acoustic isolator in the bottom-hole-assembly that can be used to mitigate or eliminate the influence of the formation boundary on the acoustic signal in drill string. The numerical results indicate that such an acoustic isolator can effectively attenuate the noise and improve the amplitude-frequency characteristics of a low-frequency signal induced by acoustic transmission along the drill string.

中文翻译：

---

钻井液与地层边界耦合对声波在钻柱中传播影响的研究

沿钻柱随钻测量的声波传输（MWD）是有效解决泥浆脉冲传输导致传输速率低的问题的方法。然而，实际的井下声波受许多因素的影响，例如钻井液的性质和地层边界，并且它们对钻柱中的声波传输的影响还没有被完全理解。为解决这一问题，提出了一种纵向振动模型，用于声波在钻柱中的传播，并考虑了钻井液的粘性阻尼和钻头与地层之间的接触的耦合作用。采用具有二阶精度的有限差分法求解数学模型。结果表明，钻井液阻尼的增加导致声波幅度线性减小，但效果不明显。地层边界主要影响钻柱通道的低频响应，而对高频响应的影响很小。基于以上分析，本文提出在井底钻具组合中增加隔声器，以减轻或消除地层边界对钻柱中声信号的影响。数值结果表明，这种隔声器可以有效地衰减噪声，并改善沿钻柱的声传输引起的低频信号的幅频特性。地层边界主要影响钻柱通道的低频响应，而对高频响应的影响很小。基于以上分析，本文提出在井底钻具组合中增加隔声装置，以减轻或消除地层边界对钻柱中声信号的影响。数值结果表明，这种隔声器可以有效地衰减噪声，并改善沿钻柱的声传输引起的低频信号的幅频特性。地层边界主要影响钻柱通道的低频响应，而对高频响应的影响很小。基于以上分析，本文提出在井底钻具组合中增加隔声装置，以减轻或消除地层边界对钻柱中声信号的影响。数值结果表明，这种隔声器可以有效地衰减噪声，并改善沿钻柱的声传输引起的低频信号的幅频特性。本文提出在井底钻具组合中增加一个隔音器，以减轻或消除地层边界对钻柱中声信号的影响。数值结果表明，这种隔声器可以有效地衰减噪声，并改善沿钻柱的声传输引起的低频信号的幅频特性。本文提出在井底钻具组合中增加一个隔音器，以减轻或消除地层边界对钻柱中声信号的影响。数值结果表明，这种隔声器可以有效地衰减噪声，并改善沿钻柱的声传输引起的低频信号的幅频特性。