Method Study Of Velocity Obtain At Complex Geology Region In The Northern Of South Sea

A sonic log represents direct measurement of the velocity with which seismicwaves travel in the earth as a function of depth.seismic data, on the other hand,provide an indirect measurement of velocity. Based on these two types of information,the exploration seismologist derives a large number of different types of velocity:interval,apparent,phase,group,root-mean-square(rms),instantaneous,normalmovement(NMO),stacking,and migration velocities. However,the velocity that can be derivedreliably from seismic data is the velocity that yields the best stack. The medium speedof seismic wave propagation is one of the significant parameters in the geophysicalexploration. For geophysicists, the objectives they’ve been always striving to pursueare to acquire a precise velocity of stratum and to transform the expected researchfindings from time-domain to depth-domain. The abyssal zone in QDN basin at theboundary of northern mainland in the southern sea, which is the falut depression basinborne in Cenozoic era. And the low amplitude is the range of profitability explorationin the abyssal zone, it’s because this zone goes along with oil source, with goodescape route of oil and gas, and the baring is very good. However,the singularitygeology structure and sedimentary environment cause the tranverse velocity changeacutely, it make the method study of exact interval velocity is very difficult withoutthe actual log data.The target zone BD3D exploration is near the south of BD sunken, the north ofSongDong sunken,standing on the overturn of SongTao bulge in the east of the QDNbasin. The trend of sea floor is falling from north-west to the south-east, the delta timeis almost270ms, the delta depth is almost200m. The CNOOC drilled the NO.1and2in2002and2010, to the3rd leng inthe LingShui geologic group.The Dix equation，Stacking velocity inversion,and Coherent inversion areresearched by deriving the fundamental principle and analysing the fault,after all, I relize the character of national ways of evaluation. the dix equation includes severalimportant faults as following:1st, it’s just suitable for the layer cake model andmicrospread offset,2nd,the seriously error magnification effect,3rd,it can’t adapt togreat changing horizontal layer model.a valid technique is proposed to resolve thequestion,The technology obtain good application results in actual seismic data fromSouth-Sea BD target area, it can resolve the question about vertical continuous andhorizontal variation, the horizon in computed profile next to the actual horizon curve,and describe the structure detail clearly. Above all, the processing system provides asolution for the development of other seismic data processing software, andcontributes to the reservoir prediction.To solve this question, I propose these ways as following:1st,adopting a newcompacted-sediment,asymptotically bounded,exponential vertical velocity model thatrepresents the effect of gradually increasing velocities with depth is proposed. Thevelocity model is constrainted by geologic condition, it can adapt to the normal seafloor structure, the abrupt changing high pore pressure and other related discontinuouszone. It can control the transverse continuance of interval velocity.2nd, creating theinterval velocity mesh configuration for inversion.3rd, defining the radius for theconstrainted inversion.4th, inserting the rms velocity and the related parameter toensure the inversion result.5th,interpolatting the velocity cube after getting the exactinversinal interval velocity.finally,we get the exact interval velocity cube andcontinue to do the following steps of seismic data analysis.The EAB model enables better control of the lateral velocity continuity becauseof the smaller number of parameters required to describe vertical velocity profiles.Above all, it can be used in many velocity analysis or inversion, such as tomographyor constrained velocity inversion. In this paper, we analyses the sensitivity of theparameter and the numerical example is good. The3D velocity inversion based onEAB velocity model can be distinguished in three types of velocity inversion:1st, novelocity discontinuities occur at interfaces,2nd, velocity discontinuities occur atinterfaces,3rd, the discontinuity at the sea bottom and discontinuities along velocityanomaly points. We apply this3D velocity inversion in the low amplitude structuralseismic data in the South Sea of China, it tell us that the fitting curve fit in with theVSP curve, and the layers in the velocity field can be see clearly. After all, we get thegeologically and stable EAB model. We can know the low amplitude structure,describe the detail of this, and attribute to the reservoir prediction.