oa Post- vs Pre-Migration Residual Velocity Analysis: a Case Study in the Gulf of Thailand

Post-migration residual velocity analysis is part of routine process in standard processing sequence for both time and depth imaging. However, decision either to proceed with post-migration residual velocity or adding another iteration of velocity update prior to migration can be a challenging issue for such as tight turnaround project or due to poor velocity control from inaccurate well information. In this case, it is often to wrap up the modelling process even before adequately reaching a minimum level of residuals and let post-migration process to handle. Managing unoptimized model after migration can be harmful for seismic image quality as the approach completely disregards migration involvement in flattening the gathers and tying to the wells. Post-migration residual correction approach covering gather flattening and depthing, is a 1D solution and therefore, to a certain degree, helpless to recover any false image associated with suboptimal 3D imaging process. Thus, when the total residual corrections from post-migration gather flattening and depthing are numerically significant, then pre-migration velocity upgrade should be considered.