Research On AVO Forward Simulation In Angle Gather And Nonhyperbolic Moveout Method

AVO technology is a better approach to indicate hydrocarbon directly and estimate lithologic parameters of crust. The Zoeppritz equation is the fundamental basis for AVO analysis. In the beginning of the second chapter, I introduce the basic principles of AVO technology firstly, and then generalize P-P wave approximations according to the Zoeppritz equations, compare the essentials, backgrounds, suppose conditions, specialties and the functions in detail, and calculate the P-P wave reflection coefficient versus incidence angle with different model of each approximations. On the basis, I discuss the basic principles and achieving steps of the method of AVO forward simulation in angle gather which makes use of the different approximate formulae of Zoeppritz equations to invert various AVO attributes. In the final part of second chapter, I study the AVO characteristic response and its change rules on three types of Gas-bearing sand.In the beginning of third chapter, I introduce a modified formula for a generalized semblance attribute, which is suitable for velocity analysis of prestack seismic gathers with AVO character. While the conventional semblance can be interpreted as squared correlation with a constant, the modified semblance is defined as a correlation with a trend. Analytical derivations and numerical experiments prove the feasibility of this method. Using synthetic and field data examples, I demonstrate the improvements in AVO velocity analysis via modified semblance. In the other part of third chapter, I show that, by estimating local event slopes in prestack seismic reflection data, it is possible to accomplish all common time-domain imaging tasks, from normal moveout to prestack time migration, without the need to estimate seismic velocities or any other attributes, and I have proved this point by using synthetic and field data examples.The hyperbolic approximation of P-wave reflection traveltimes in common-midpoint gathers plays an important role in conventional seismic data processing and interpretation. It is well known that the normal moveout formula is based upon homogeneous isotropic media. The conventinal hyperbolic approximation of P-wave reflection moveout is exact for homogeneous isotropic or elliptically anisotropic media above a planar reflector. Any realistic combination of heterogeneity, anisotropic coefficient, and nonelliptic anisotropy will cause departures from hyperbolic moveout at large offsets. Therefore, nonhyperbolic moveout gives exact traveltimes for elliptically anisotropic media overlaying a plane dipping reflector. In the forth chapter of this paper, I show a theoretical description of P-wave reflection traveltimes and compare the degree of nonhyperbolic moveout with different anisotropic parameters.Velocity analysis is a primary component in seismic data processing. Isotropy is used in conventional velocity analysis. But 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, the nomal moveout velocity is not equal to the real imaging velocity, the events is not flat in CMP, CRP and CIP gathers. Ignoring of anisotropy will lead to the information missing in steep-dip stratum, so we adopt the bi-spectral residual velocity analysis method, which is based on VTI medium and can correct the far-offset event. And in the fifth chapter of this paper, I have explained the principles and processes of Bi-spectral residual velocity analysis method deeply, and discussed the effect of the application in detail. After modification, the information of far-offset event will be corrected. Apart from that, Bi-spectral residual velocity analysis can even improve the S/N ratio and resolution. It can provide more effective information in the following processing, such as AVO analysis.