Residual Statics using CSP gathers

Xinxiang Li, John C. Bancroft

All the conventional methods for residual statics analysis require normal moveout (NMO) correction applied on the seismic data. The statics estimates from these methods are affected by the inaccurate velocity information and the NMO time variant effects. These can be easily demonstrated by experiments with different NMO velocity fields and with different horizon pickings.

We present a new method that is designed to estimate residual statics before NMO correction. This method is based on the concept that migration and its inverse operation (modeling) can provide reference correlating traces for the undesired timeshift estimation.

Equivalent offset migration (EOM) technique introduces a new way to perform pre-stack Kirchhoff time migration. An intermediate step of this migration is to construct a new pre-stack data volume called CSP gathers. This construction process is a partial migration process that does not involve any time direction energy distribution. This no-time-shift partial migration and its inverse operation make up a faster and better way to create static model data by "migration-modeling" technique. And, the partial migration and its inverse operation are both insensitive to preliminary velocity information. In addition, an asymptotic solution for the CSP gather construction, which is basically related to post-stack migration, is totally velocity independent.

We present some results from synthetic and real seismic data. The statics estimatedby our method are comparable to the results from conventional methods.