Residual error correction in common imaging gathers for prestack migration: Sand area example, Qinghai field, China

Abstract

Summary Near surface velocity and layer thickness variation cause time anomalies that can be approximated as surfaceconsistent static time shifts. The conventional methods for residual static estimation are based on NMO corrected data, where all traces in a CMP gather are supported to have similar structures. However, pre-stack Kirchhoff time or depth migration is to time shift all input traces within the migration aperture for aligning horizontally their reflection events by using a good velocity model without structure assumptions, before stacking for generating common imaging gather (CIG). These corrected traces provide a powerful dataset to estimate the residual error and maximizing the stack power of a CIG stack. Also, migration by applying the residual error corrections at CIG can provide us with high solution imaging compared to the conventional methods. In addition, it can make the traveltime error up because of an inaccuracy shallow velocity model. Using this approach into real data, which was acquired in the sand land, Qinghai filed of China, shows us that the reflection event continuities and imaging resolution of the pre-stack Kirchhoff migrations are improved.