由实验和理论给出了应力集中是如何影响钻孔周围速度场,以及速度场是如何影响偶极各向异性测量的。在低频率,偶极波主要易受远场应力的作用,即标准声波测井解释结果恰能得出最大应力方向。在高频率,偶极波主要受近场应力集中的影响,致使快速极化方向与最小构造应力的方向一致。这些效应使得在快速极化方向和慢速极化方向测得的偶极波散曲线产生了交叉。根据宽频带偶极资料,偶极波散曲线交叉可被用来作为应力诱发各向异性超过弱的固有各向异性的标志。 Experiments and theories show how stress concentration affects the velocity field around the borehole and how the velocity field affects the dipole anisotropy. At low frequencies, dipole waves are predominantly subjected to far-field stresses, ie, the results of a standard sonic well log interpretation yield just the maximum stress direction. At high frequencies, dipole waves are mainly affected by near-field stress concentration, resulting in a direction of fast polarization consistent with the direction of minimum tectonic stress. These effects cause crossovers in the dipole dispersion curves measured in the fast and slow polarization directions. Based on the broadband dipole data, dipole dispersion curves can be used as a sign of stress-induced anisotropy over weak intrinsic anisotropy.