Study On3-D Velocity Analysis

In high precision seismic exploration,fine Superposition is an important step, whichcan only be achieved when accurate stacking velocity is obtained..The stacking velocity isvarying versus the azimuth angle in the3-d seismic exploration, ignoring it and using thehyperboloid of revolution to fit the time-distance curve when conduct the NMO andvelocity analysis will cause some error on the stacking velocity in different azimuth anglewhen the interface is sloping. The inaccurate velocity would not only lower the stackingamplitude, but also distort the waveform and affect the quality of the stacking signal;Onesignificant advantage of the3-d seismic exploration is the abundant information itcontains,therefor ignoring the stacking velocity varying means ignoring much usefulinformation, Therefore ignoring the variety of stacking velocity means neglecting muchuseful information, which makes the3-d seismic exploration unable to play its full use.sobuilding the accurate3-d velocity field is of great significance to the fine seismicexploration and gaining the parameter of the underground layer.First carrying out some analysys and calculation about the resuilt and the error whenusing an identical velocity for NMO and stacking, mainly considering the influence in thestacking signal and the velocity spectrum,these mainly related with the arrangementmode,stratum geological parameters sucn as the dip and the trike,when the arrangement islonger,the azimuth included is more,the dip is bigger,then the erroe is bigger and thestacking signal is more bad,then explain the importance to consider the velocity varyingwith the azimuth. Another problem in the3-d seismic exploration is the resolution of thevelocity spectrum. To solve this problem, the eigenvalue velocity analysis can be applied to3-d velocity analysis, which would improve the resolution of the velocity spectrum as wellas noise attenuation.The distribution of the stacking velocity is related with three parameters, which are the RMS velocity,angle,trike respectively,this paper introduced two methods to gain thesethree parameters.The first method is the sector analysis method,gain the three parametersthrough extracting profile in more than three azimuth and conduct the velocity analysis;thesecond method is the iterative scan about the three parameters.Desirable resuilt obtainedwith model test improved these two methods are effective,and the iterative process isconvergent，then can build the velocity field with these three parameters.The traditional stacking profile is obtained from extracting CMP gather,and thenthrough velocity analysis,NMO,stacking,when the underground structure iscomplicated,the CRP is diverging,and the gather is not the really CRP gather,the PROmethod is directly handle with the common shot record,and the stacking gather is the reallyCRP gather.Desirable resuilt are obtained when this method applied in the3-d seismic dataprocess,it have advantage in noise attenuation compared with the2-d method.