Integration of Geology and Geophysics for Subsalt Post-Stack Inversion

There are many challenges in the subsalt areas such as low signal-to-noise, uncorrected seismic velocity and poor illumination. One of the main goals of seismic inversion in the subsalt areas is to obtain high resolution relative and absolute impedance for reservoir properties prediction. In order to understand whether seismic inversion of wide azimuth (WAZ) wave equation migration (WEM) seismic data is robust enough to estimate reservoir characterization and reservoir development in subsalt areas, we performed the post-stack inversion in 50 OSC blocks in Green Canyon, approximately 481.25 square miles. A total of three subsalt wells and four subsalt seismic interpreted horizons were used in the inversion process. The other well was used for blind test. Our post-stack inversion method used iterative discrete spike inversion method based on the combination of space adaptive wavelet processing (SAWP) to invert for relative acoustic impedance. Then, the dips were estimated from seismic and converted them to a horizon-like, layer sequence field (LSF) that was used as one of the inputs into the low frequency model (LFM). The background model was generated by incorporating the well velocities, seismic interpreted horizons and the previously derived layer sequence field in the low frequency model. Then, the relative acoustic impedance volume was scaled by adding the low frequency model to match the calculated acoustic impedance logs from the wells for absolute acoustic impedance. Subsequently, the geological information and rock physics were incorporated into the reservoir properties assessment for sand-shale prediction in two main target reservoirs in the Gulf of Mexico in the Miocene and the Wilcox formations. Overall, the post-stack inversion results and the sand-shale prediction showed very good tie at the well locations, especially in the blind test well. Hence, the approach of incorporating rock physics and geology enables the post-stack inversion in subsalt areas.

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California