Study On Angle-domain Kirchhoff-type Migration

Kirchhoff prestack depth migration is an important tool for seismic explorationin complex media. But its precision is influenced by the accuracy of the initialvelocity model and the signal-to-noise of the original data, and the accuracy of themigration operation. To obtain the accurate velocity model is one of the goal of theseismic processes, throughout the whole process of seismic exploration tasks.In order to get a highly accurate velocity field, we need to proceed prestackmigration velocity analysis. Then velocity analysis usually uses the CIGs to correctthe original velocity model. When the value of the velocity model is not accurate, theevents of the CIGs will bend. But when the phenomenon of multiarrivls exists, theaccuracy of the velocity field will have errors though the events is straight. CIGs inangle domain describe the angle between the incident ray and the normal of theinterface, which uniquely ensures the ray path. So it can deal the problem ofmultiarrivals. So far, CIGs in angle domain is meetly suited to the migration velocityanalysis and amplitude analysis.In order to get a highly accurate velocity field, weneed to proceed prestack migration velocity analysis. Then velocity analysis usuallyuses the CIGs to correct the original velocity model. When the value of the velocitymodel is not accurate, the events of the CIGs will bend. But when the phenomenonof multiarrivls exists, the accuracy of the velocity field will have errors though theevents is flat. CIGs in angle domain describe the angle between the incident ray andthe normal of the interface, which uniquely ensures the ray path. So it can deal theproblem of multiarrivals. So far, CIGs in angle domain is meetly suited to themigration velocity analysis and amplitude analysis.Ray tracing method is mainly used to calculate the seismic wave propogating ina media about traveltimes, ray paths, and amplitude in the seismic wavefield numerical modeling.Traveltimes and ray paths can be calculated by kinematic raytracing and amplitude can be obtained by dynamic ray tracing. Among so many raytracing methods, wavefront construction method is the one that can calculate seismictraveltimes, ray paths, and amplitude in the meantime. Comparing with thetraditional ray tracing method, this method’s independent variable isn’t the arc lengthbut time. So it can acquire the seismic traveltimes and ray paths in the undergroundmedia at the same time.We obtain the angle gathers based in the wave-front ray-tracing in Kirchhoffmigration. And at the mean time, we obtain the migration profiles. Thus in this paper,we study the methods through three contents as followings:(1) we summary the dataof the seismic reflection and the characteristics of different gathers;(2) we also sumup principle of extraction of the CIGs. And we compare the specialty of method ofthe extraction through the Kirchhoff migration with the method of wave equationmigration.(3) Last, we extact the angle common-angle gathers based on thewave-front ray-tracing, and use the angle gathers to make Kirchhoff prestack depthmigration.The result of prestack Kirchhoff migration by abstracting the angle domaincommon image gathers from the different seismic data, proves that the angle-domainKirchhoff migration can be applied in migration. In future, the method should beused in the inhomogeneous velocity model, and consummates the ray tracing methodto diffract the quality of migration.