VSP reverse-time migration using two-way nonreflection wave equation
Zhu Jinming Dong Minyu Li Chengchu
VSP data are usually recorded in common-shot gather and contain less informations.It is difficult,therefore,for us to obtain good mig- ration result by using conventional migration methods.Both inner in- terface reflections and interformational multiples can be removed by reverse-time migration with the use of two-way nonreflection wave equation;besides,boundary reflection in VSP can be eliminated using Clayton's absorption boundary condition.It is proved that reverse-time migration is able to improve migration quality.The imaging condi- tion is still obtained by generalizing Claerbout's imaging principle and solving eikonal equation.This is a very practical wave equation migration method.This method is applicable to prestack VSP data, conventional multiple-offset shot gather and the simultaneous migra- tion of VSP data and surface seismic data.Besides,it is adaptable to various velocity variations. Before applying the method to VSP data processing,we should fi- nish the following processing work:muting the first arrivals,tailing the boundary traces(or putting a damping on boundary traces),inter- polating traces,frequency filtering etc.;otherwise we'll fail to make good VSP migration.