Study On P-wave Multi-component NMO Velocity Of3D Gathers Model In Complex Media

According to propagation characteristics of P-wave multi-component in3D gathers in complex media, in this thesis, I start with the hyperbolic time-distance of P-wave in CMP gathers of horizontal reflection interface in isotropic media, from simple to complex, from horizontal interface reflection to complex interface reflection of common inclined, from P-wave CMP gathers to multi-component of P-wave CRP gathers, and then to P-SV component and CCP gathers, get time-distance relationship and NMO velocity. On such basis, this paper extends the study of time-distance relationship and NMO velocity to anisotropic media. Moreover, this analyzes time-distance relationship and NMO velocity of multi-component of P-wave in TTI media, like VTI media and HTI media.Referring to the study of anisotropic and NMO velocity at home and abroad, by analyzing the research statues, research method and the problem to solve, I noticed that the treatment of slant interface gathers in the past mostly were approximateWith the isotropic horizontal interface or CMP gathers, while TTI media with dipping symmetric axis is common in real formation. That will lead to bad result of approximate treatment. To analyze the propagation law of elastic wave in anisotropic media, I compare the elastic parameters of variety P-wave components of3D gathers with anisotropic parameters by Thomsen parameter and Tsvankin parameter.The hyperbolic time-distance relationship of P-wave CMP gathers of horizontal interface in isotropic media is the foundation of the model research. The NMO velocity shows elliptic characteristics in plane. The time-distance equation of P-wave CRP gathers is similar to the approximate formula of time-distance equation of P-wave CMP gathers. While the ratio between offset and depth in the direction normal from common reflection point of CRP to three-dimensional dipping interface(X/H) is less than2, we can get the morphological parameters of interface and travel time of P-wave CRP by using the iteration method. The formula of approximately hyperbolic travel time of P-wave CRP is the function of offset distance and apparent dip. Moreover, the NMO velocity of P-wave CRP gathers in a variety of azimuth angles of the survey lines shows the characteristics of elliptic, and the NMO velocity of which is decreasing while the dip angle of3D inclined interface is increasing. The model tests show that when X/H is smaller than1.6, the approximate hyperbolic curve of travel time of P-wave CRP gathers can be dynamically corrected to a plane at all directions line.This paper applies the approximate method to deal with time-distance relationship of theory parameters of P-SV component and CMP gathers of the converted wave, and the accuracy of the travel time decreases with the increase of the ratio of offset distance to the P-wave or S-wave. Inversion morphological parameters of3D inclined interface, azimuth of survey line and velocity by time-distance equation of P-SV component of the converted wave. The NMO velocity of the study P-SV component shows elliptic characteristics. For P-SV component CCP gathers, the iterative method is available to get morphological parameters of model and travel time of gathers, and its time-distance curve is approximate to hyperbolic, which is similar to that of P-wave CMP gathers. The approximate hyperbolic travel time is close to theoretic travel time while the time-distance of P-SV component CCP gathers is not far offset distance. The NMO velocity of P-SV component CCP gathers of the converted wave produces elliptic curve during the variety of dip angle line. Moreover, the NMO velocity of that is decreasing with the increase of the dip angle of3D inclined interface. When ratio between offset and depth in the direction normal from common convertion point of CCP to three-dimensional dipping interface (XIH) is less than0.8, the curve of travel time of P-SV component CCP gathers of the converted wave can be dynamically corrected to a plane at all directions line.On the basis of the relationship between the symmetry axis of TTI media and3D inclined interface, the travel time of the components of P-wave in anisotropic media can be expressed as the travel time of the components of P-wave in isotropic media plus the variety travel time of the perturbation in the asymmetric direction. Calculating NMO velocity of components of P-wave in anisotropic TTI media by the second derivative of the offset distance to travel time, I find that their NMO velocity is both elliptic. That is to say, no matter the symmetry axis of anisotropic TTI media is parallel to or vertical to the normal 3D inclined interface, the NMO velocity is elliptic. The NMO velocity of CRP gathers in TTI media is influenced by the strength of anisotropic and value of the dip angle of3D inclined interface mostly. The maximum of the NMO velocity and the direction of the symmetry axis of elliptic is not sensitive to the dip angel, while the minimum one is decreased rapidly with the increase of the dip angle. The NMO velocity of P-wave CRP gathers in anisotropic TTI media is bigger than that in isotropic media.3Dseismic data processing should take anisotropic and the variety of reflection interface into account.