井间地震导波速度特征研究

A study of the velocity characteristics of cross-hole seismic guided waves

本文研究了井间地震勘探中单界面和低速层导波的速度特征。理论分析说明，单界面可能会存在一种不均匀衰减但不频散的漏能振型波，而不存在Stoneley波。本文推导了低速层导波的频散关系。数值模型计算表明，低速层导波是频散的，其频散关系和相速度大小是与地层速度结构、厚度密切相关的。在相同频率处，可能存在具有不同截频的多阶振型。

In the paper, the velocity charactedstics of guided waves along single interface and low-velocity lay-er in cross-hole seismic surveys are researched. The theoretical analysis shows that there may exist an in-homogeneous, attenuating but non-dispersive leaky-mode guided wave along the single interface while there is no Stonley wave present. We deduce the dispersion relation of the. guided wave along low-veloc-ity layer in the paper. The numerical modeling indicates that the guided wave along low-velocity layer is dispersive, which dispersion relation and phase velocity are closely related to the velocity structure andthickness of strata. At the same frequency, there may be multiple order modes with different cut-off fre-quencies.