Elastic-Wave Imaging Using P-P, Sh-Sh, and Sv-P Events: Modeling and Data Processing
Ermolaeva, Elena 1988-
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This thesis focuses on using seismic data that were generated by a vertical vibrator and recorded by a vertical geophone to build two different subsurface images: a conventional P-P section and a converted-wave SV-P section. Radiation patterns are calculated based on Miller and Pursey’s equations that show P- and S-wave radiation from a vertical point source. Elastic modeling is performed for simple models to study the P- and S-wave modes propagating within the medium and to test the effectiveness of an SV-P processing flow. This special flow is designed to carefully attenuate noise and P-P signal while keeping the low-frequency SV-P signal intact. The processing builds separate P-P and SV-P subsurface images. The original vertical-vertical and an additional pure shear (SH-SH) datasets were processed to obtain 2000 m P-P, 350 m SV-P, and 500 m SH-SH depth images, their corresponding velocity fields, and Vp/Vs values (Vp/Vs=6 on average). The resulting images are tied to the interpreted shallow 140 m well logs for quality control of the data processing and compared. The P-P and SH-SH images tie well with the conductivity logs and accurately show the targeted shallow sand intervals. The SV-P image features similar reflectors as the P-P and SH-SH images. These SV-P events, although less continuous, provide subsurface information down to about 300 m depth and have better resolution in the shallow part of the image compared to the P-P image. Despite several drawbacks of this method, there is promise in SV-P extraction and imaging especially for shallow targets with all of the benefits of the converted-wave seismic method.