RESIDUAL MIGRATION VELOCITY ANALYSIS IN THE OFFSET-DEPTH DOMAIN

摘要

Migration velocity analysis in the offset-depth (x-z) domain usually requires top down layer stripping migration. Here we propose a method of velocity analysis using data already migrated with an initial trial velocity. By analysis of the offset-depth residuals in the migrated common image gathers (CIGs) we show how to interactively update the velocity depth model. For each common image gather (CIG) we first create a mapping of ray parameters (p) as a function of depth (z) using a local 1D assumption. We calculate the residual migration depth corrections in the p-z domain and map these depth corrections back to the x-z domain to test trial velocities using the previously migrated CIGs. Since we calculate the residual migration depth corrections in the p-z domain, the interval velocities are derived directly by top down residual migration. Hence we do not have to explicitly do a layer stripping migration to isolate the interval velocity corrections. Applications on synthetic and real data show that the analysis of the residuals followed by remigration of the original data produce an excellent result.