Imaging of 3-D Three-Component Vertical Seismic Profile Data Based on Horizontally Layered Azimuthally Anisotropic Media

Three-dimensional (3-D) three-component (3D3C) vertical seismic profile (VSP) survey has been widely implemented recently. Nevertheless, realizing the joint imaging of VSP PP- and PS-waves considering anisotropies is still problematic. Unlike ground 3-D seismic data, which are rich in source-receiver orientations, the receivers of 3-D VSP are positioned in a well, and only the distribution of sources is multidirectional. Therefore, the data processing methods considering azimuths for ground seismic data are barely applicable to VSP data. We proposed a joint imaging method based on prestack time migration (PSTM) for 3D3C-VSP PP- and PS-waves of horizontally layered azimuthally anisotropic media and presented the detailed strategies to update migration velocities and correct the anisotropy effects on the moveouts of image gathers. The theoretical basis of our method is the azimuth-dependent moveout equation of ground PP-wave, which was shown to be applicable to borehole PP- and PS-waves. In the imaging process, the VSP upgoing PP-, PSV-, and PSH-wave shot records were first divided into different shot point-image point azimuth sectors, where PSTM was performed to produce common image point (CIP) gathers and implement anisotropic migration velocity analyses. The correction of the anisotropy effects on CIP gathers was aimed at two aspects. One is the moveout anomalies jointly induced by horizontal layering and fractures, and the other is PS-wave splitting. We applied the proposed method to a synthetic dataset and an actual work area, demonstrating that it can produce high-quality anisotropic migration results of PP-, PS1-, and PS2-waves, and predict fractures reliably.