Study On High Precision NMO And Velocity Analysis

Underground medium is assumed isotropic when traditional data processing is conducting, however, seismic anisotropy will have a significant impact on wave propagation and data processing. Seismic anisotropy is widespread, mainly in the shale and broken rock, and also anisotropy can reflect the actual seismic model.NMO correction and velocity analysis are the basic steps in the seismic data processing.This article we studied on the high-precision NMO correction and velocity analysis of vertical transversely isotropic (VTI) media. First we reviewed the development history and current situation of seismic anisotropy NMO dynamic correction and velocity analysis,then given an overview of the significance and research ideas of this article.We studied high-precision NMO correction method of the large aperture horizontal layered VTI model.Based on travel time formula of VTI media,we contrasted the conventional NMO correction results of different formula.Although optimization formula improved the accuracy of the NMO correction to a certain extent, this change did not bring a substantial role in our process because the NMO stretching phenomenon has not been eliminated.The reason for NMO stretching is that wavelet itself has a certain length,therefore,time difference of shallow is larger than deep.Because of the middle point of wavelet unable to be determined after conventional NMO,the theory of anti-NMO stretching still has some defects.That is,at the same with traditional methods,stretched wave must be muted off before stack.In order to eliminate NMO stretching occurred by the conventional NMO correction, we studied on the constant normal-moveout(CNMO) method and longitudinal optimization normal-moveout.CNMO is obviously different from conventional NMO because CNMO performs NMO correction by applying a constant Δtnmo.Following the CNMO correction, muting may be significantly less severe compared with conventional NMO.Therefore, longer spreads of data may be used for CMP stack, velocity and AVO analysis, thus improving their resolution. Longitudinal Optimization NMO correction avoided false seismic event of long offset seismic traces affected by CNMO.At the same time,it also can make up correction deficiency caused by travel time formula.The significance of velocity analysis can never be overemphasized.Only with exact velocity analysis,the results of NMO correction, stacking and even migration can be more credible and more realistic to reflect the actual subsurface structure.Otherwise, the error of the velocity analysis will lead to more serious genetic error, which led to the process results not be trusted and greater difficulties to the interpretation of the data.Conventional velocity analysis method based on central point of wavelet, which has some shortcomings because central point travel time is not the real travel time of wavelet.Therefore, the stacking velocity scanned by central point travel time has greater error.this article based on the theory of first arrival time we modified traditional similarity coefficient formula and contrasted different result of two similarity coefficient formula.Numerical results of model shows that first arrival point travel time velocity and η inversion method can improve the retrieval accuracy Effectively,the result of this theory is more credible.