Mohanad E. Drais, Amer Al-Khalidy
Pre-stack depth migration is an important method for accurate subsurface imaging in areas with complex structures and strongly lateral velocity changes. In the North Ekhaider area of Western Iraq, seismic imaging is greatly affected by variations in the velocity of the weathering layers. These variations cause conventional time-domain results to be mispositioned and poorly defined structurally. This study worked on building an accurate initial Earth model and applying iterative updates via tomography inversion, combined with Kirchhoff Anisotropic Pre-stack Depth Migration under a Tilted Transverse Isotropy assumption. The near-surface velocity model was built from deep-hole data to represent lateral and vertical heterogeneity. The deeper velocity model was built depending on the final velocities of the Pre-Stack Time Migration. These two models were merged, and Thomsen’s anisotropic parameters (ε and δ), together with dip and azimuth information, were incorporated to generate the TTI earth model. The quality control is performed after the update of each tomography by checking the well mis-tie, comparing the updated velocity with the well velocity, and the flatness of reflectors in the Common Image Point gathers to ensure accurate event focusing. The final KAPSDM image demonstrates an improvement in the subsurface focusing, minimizing mis-ties and eliminating pseudo structures caused by unresolved near-surface anomalies. This workflow has proven effective in structural and stratigraphic interpretation in the North Ekhaider field by obtaining a high-resolution subsurface image.