Tomographic velocity analysis of PP- and PS-waves for VTI media: Field-data application

Mode-converted PS-waves can provide valuable information for anisotropic parameter estimation that cannot be obtained from compressional waves alone. In a previous paper, we developed an efficient tomographic methodology for 2D joint velocity analysis of PP and PS data from VTI (transversely isotropic with a vertical symmetry axis) media. The algorithm is designed to flatten image gathers of PP-waves as well as of pure SS reflections computed using the PP+PS=SS method. An important additional constraint is provided by codepthing of the migrated PP and SS sections. The model is divided into square cells, and the parameters VP0, VS0, ε , and δ are defined at each grid point. Here, this methodology is applied to multicomponent data recorded on a 2D line from an OBS (ocean bottom seismic) survey acquired at Volve field in the North Sea. Although the parameter-updating procedure did not include any borehole information, the VTI model obtained by joint tomography of the recorded PP-waves and constructed SS-waves produced generally well-focused PP and PS depth images. The depth consistency between the migrated PP and PS sections also corroborates the accuracy of the velocityanalysis algorithm.