偶极源井孔声场中纵横波的计算及分析

Numerical Simulation and Analysis on The Compressional and Shear Wave Excited by A Dipole Source in Borehole

在分析垂直割线和极点对偶极源井孔声场中分波和全波贡献的基础上,给出了数值计算纵横波部分的方法,即纵波是纵波垂直割线和复极点的综合贡献,而横波是横波垂直割线和实极点构成的传播模式的贡献。结合实际算例对该方法的正确性进行了验证,指出了以往应用垂直割线积分计算纵横波的局限性。对纵横波部分的频率激发谱和传播行为进行了分析,结果表明在泊松比较大的慢速地层中复极点对纵波头波的贡献较大;横波的幅度及横波垂直割线和实极点对横波的贡献大小随声源的激发频率发生变化。

After studying vertical branch cuts and pole contributions to the borehole wave field, a method of separating compressional and shear wave arrivals is provided. Numerical results demonstrate that contributions of complex poles together with compressional branch cut integration represent the compressional wave arrival, while the contributions of real poles incorporated with vertical shear branch cut integration may be considered as shear wave component. The validity of this method was verified by real algorithm examples, and limitation of the method of calculating compressional and shear wave arrivals by vertical branch cut integration was given. The wave components both in the time and frequency domain are analyzed, the result of which shows that the contributions of complex poles to head wave are larger for slow formations with larger poissons ratio, and center frequencies of the sources influence amplitude of the shear wave arrival, the contributions of real poles, and vertical shear branch cut.