不同偏振方向的偶极子声源在HTI地层井孔中激发声场的实验研究

本文首先制作了TI地层模型井,对模型井的速度、密度等物理参数进行了测量,通过快速模拟退火算法得到了该介质的五个TI刚性系数,然后采用缩尺的偶极子探头在HTI地层井孔内进行超声测量实验模拟了实际的偶极子声波测井,并结合数值模拟的结果,研究了不同偏振方向的声源在HTI地层井孔中进行偶极子声波测井的响应特征.模拟结果表明,弯曲波的幅度和速度随声源的偏振方向不同而不同.正交分量的波形幅度在声源偏振方向平行或垂直于快横波面方位时最小,在与快横波面方位呈一定夹角时较大;同向分量波形幅度随声源的偏振方向的变化规律同正交分量相反.弯曲波速度在声源的偏振方向与快横波面方位的夹角小于30°或者大于60°时,分别接近于快弯曲波和慢弯曲波的速度,对于夹角的变化不敏感;当夹角在30°和60°之间时,弯曲波的速度对该夹角变化非常敏感,由接近快弯曲波速度快速变化到接近慢弯曲波速度.

Experimental study of the acoustic field in the borehole surrounded by HTI formations excited by dipole sources with different orientations

We firstly made several TI borehole model wells,and measured the compressional, shear velocities and density of the material. The equivalent TI elastic parameters were obtained by a fast simulated annealing algorithm. Then we simulated dipole acoustic logging by ultrasonic measurement experiments in the borehole surrounded by a HTI formation using small-scale dipole transducers. Combined with numerical simulation results, the influence of the orientation of dipole sources on acoustic logging response is analyzed. The results showed that the amplitude and velocity of flexural waves changes with the orientation of dipole sources. The amplitude of cross-line waveforms gets the minimum when the orientation of dipole sources is perpendicular or parallel to the fast shear direction, and is relative large when the angle between the orientation of dipole sources and the fast shear direction is neither 90° nor 0°. The variation of inline waveform amplitude is contrary to that of the cross-line waveforms. When the angle between the orientation of dipole sources and the fast shear direction is less than 30° or greater than 60°, the velocity of the flexural waves is close to that of fast flexural waves and slow flexural waves respectively, and it is not sensitive to the angle. When the angle is between 30° and 60°, the velocity is quite sensitive to the angle, and rapidly changes from the velocity of fast flexural waves to the velocity of slow flexural waves as the angle increases.