裸眼井中弹性波传播的非对称模式的数值研究

本文从数值上研究了裸眼井中弹性波传播的非对称模式,给出了合成微地震图和导波（弯曲波）的频散曲线,发现在“硬”地层和“软”地层的井中,导波都是高度频散的,其最大相速度等于地层的横波速度,其截止频率低于对称模式的伪瑞利波的截止频率;在低频（2-3kHz）和长源距（3-4m）的条件下,由非对称的声源（如声偶极子）所产生的微地震图中,初至信号是以横波速度传播的,而以纵波速度传播的信号被抑制。本文的结果对研制横波速度测井仪是有意义的。

A NUMERICAL STUDY OF ASYMMETRIC MODES OF ELASTIC WAVE PROPAGATION IN A FLUID-FILLED BOREHOLE

A numerical investigation of asymmetric modes of elastic wave propagation in a fluid-filled borehole is treated in this paper. The dispersion curves of guided waves (called flexural waves) and synthetic microseismograms are presented. The guided waves are found to be highly dispersive, with the phase velocities decreasing from the formation shear wave velocities in both hard and formations, They have much lower cut-off frequencies than the pseudo-Rayleigh waves in axisymmetric modes of propagation. We found that under conditions of low frequency (2-3 kHz) and long source-receiver separation (3-4 m), the flexural wave is the prominent arrival in a microseismogram generated with an asymmetric source, traveling with a phase velocity equal to the formation shear wave velocity, while the compressional wave arrival before that is generally suppressed. The results of this study may be meaningful for designing a shear wave logging tool.