Sensitivity analysis of seismic depth migrations: Complex structural models

Accurate velocity estimation is essential for successful seismic depth migration. There is a need to quantify methods for determining the effect of velocity on depth migration since velocity errors will ultimately lead to improper positioning and poor focusing of migrated reflection events. We describe mathematical relationships between inaccurate input velocities and depth positional errors on the migrated section. Additionally, we perform sensitivity analysis for velocities derived from prestack depth migrations. As a final step, we examine the migration errors for realistic Canadian Foothills model seismograms. Results demonstrate that systematic velocity errors, rather than random errors, are problematic, especially with prestack depth migration. In practice, an iterative and interpretive approach is needed in order to refine images of complex folds and faults. Our results identify the need to quantify uncertainties in migrated images in order to help assess the risk involved in hydrocarbon exploration and development.