Research And Effect Analysis On High Precision Velocity Analysis Methods

In high resolution seismic data processing, high resolution velocity analysis is an important procedure. Conventional velocity analysis methods generally carry out velocity analysis using coherence measures, which don't take interference events, AVO and non-hyperbolic moveout into account and didn't consider the influence of non-random noise. As to similar or interference events, there is maximum value of the stacking energy within a rather large range which effected the time-velocity resolution. Just for this reason, we should develop some new velocity analysis method suitable for different situations. At first, the basic principles of some conventional velocity analysis methods are described, the criteria of their algorithms is discussed. Based on this, we discuss some factors affecting the resolution and accuracy of velocity analysis, including spread length, signal to noise ratio, velocity sampling interval, NMO stretch removal factor, width of time window and fold number.Because of the deficiency of conventional velocity analysis, phase correlation velocity analysis method which can effectively improve the time resolution and velocity resolution of velocity spectrum is studied. After introducing the background, principle and algorithm, we conduct test and calculation using synthetic and real data. The results show that the method has higher resolution in velocity and in time and has better anti-noise property compared with conventional methods.Based on the conventional semblance method, we introduce a modified formula for a generalized semblance attribute, which is suitable for velocity analysis of prestack seismic gathers with AVO character. This method is not affected much by the anomalous amplitude and allows for accurate velocity picking. Conducting test and calculation using synthetic and real data demonstrates the improvements in AVO velocity analysis via modified semblance method. For real data, anisotropy is well known in subsurface medium. As the moveout curve is nonhyperbolic because of the anisotropy in different scales, especially large offsets or steep dips, we adopt the anisotropy velocity analysis method, which is dominated by NMO velocity Vn mo and anellipticityη. Based on the principle and algorithm of this method, anisotropy velocity analysis software is developed, which can perform conventional hyperbolic NMO and non- hyperbolic moveout. Conducting test with synthetic data demonstrates the feasibility of the software. The effect of the application in field data shows that the information of far-offset event can be greatly corrected. Apart from that, anisotropy velocity analysis can greatly improve the S/N ratio and resolution and can provide more effective information in the following processing.