Prestack Reverse Time Migration And The Research Of Removing Artifacts

At present, Kirchhoff migration and one-way wave-equation migration havebeen the workhorse methods for prestack depth migration.Kirchhoff prestack depthmigration is based on the high frequency of the wave equation approximation,Inaddition, using ray tracing to approximate the Green’s function of wave propagationcan compromise the accuracy of Kirchhoff migration, especially when the wavefieldis complicated. Its further approximation, choosing a single ray arrival of thecomplicated wavefield at each image location guarantees a noisy image in areas ofmany ray arrivals. Multiarrival Kirchhoff migration algorithms overcome thisproblem.One-way wave-equation migration (OWEM) decompose seismic wavefieldsinside the earth into upgoing waves and downgoing waves under the assumption of nointeraction between these two wavefields; that is, no turning wave or verticalreflection generation during the synthesis of wave propagation. For a very large andgrowing body of examples,OWEM has solved the problems of multiarrivals betterthan single-arrival Kirchhoff migration.Reverse time migration which extrapolates inthe time direction to become a research hotspot.Theoretical advantages such as dipunlimited accurate wave propagation and improved amplitudes have providedsignificant imaging benefits in practice. For example,in complex subsalt and salt flankareas,the numerical Green’s function from the finite-difference solution of thetwo-way wave equation has better amplitude behavior. In addition to the ability tohandle extreme velocity complexity.In this paper, the study focuses on low-frequency noise in reverse timemigration, including the application of Poynting vector imaging conditions andremoving noises after imaging. The dissertation is mainly devoted to the followingprogress：1、Because of the highly intensive computation cost and massy memorydemand, we analyze the generation principle of reverse time migration with randomboundaries.2、Comparison with one-way wave,reverse time migration has the imagingadvantages of steep dips and complex geological structure and we point out that itsthree major issues, especially the low frequency noise generation mechanisms andcharacteristics.3、Using the theoretical numerical model to complete the spreadsheet andverify the effectiveness of the Poynting imaging conditions.4、Spatial domain high-pass filtering and derivative filtering can achievedenoising purpose, but they would destroy the effective information.5、The denoising effect is obvious when we use laplace.It is relatively simpleand fast to realize.