Anisotropic Parameter Estimation Method Of QP Wave In VTI Media

The vast majority of seismic data processing theories and methods have been established based on the framework of the approximation hypothesis of acoustic waves in isotropic media for many years.This simplification reduces the difficulty of mathematical modeling for describing complex geological problems,and great achievements have been made in geophysical petroleum exploration in the past few decades.For instance,the classical stacking velocity analysis,dynamic correction,horizontal stacking and other technical means are still playing huge roles in the industry.However,with the continuous improvement in sophistication and refinement of exploration targets,particularly with the recent sharp drop in oil prices and severe reduction in exploration investment in recent years,the focus of research is turned to the exploration for unconventional reservoirs.Thus,the actual heterogeneity of the earth media must be considered.The earth media are complicated nonhomogeneous media,generally having varying degrees of fluctuation anisotropy.Seismic anisotropy is mainly reflected by that the velocity of seismic wave propagation is a function of propagation direction.In addition,anisotropy has also impacts on the polarization direction of seismic wave propagation and amplitude energy absorption attenuation.Given the complexity of the actual earth media,errors are inevitable using the conventional processing methods under the assumption of isotropy,and imaging results can be affected.Therefore,developing the seismic data processing techniques for complex media,especially for anisotropic media is absolutely necessary.In this paper,the anisotropic theory is firstly summarized and described,explaining the classification and geological signification of anisotropy,introducing anisotropy parameters and their physical significance,and deriving propagation velocities of seismic waves in anisotropic media according to wave equations(phase velocity and group velocity).Subsequently,the seismic wave propagation law and description method are studied,introducing four classical approximate formulas for travel-time curves: the trans-elliptic approximation nonhyperbolic moveout equation based on group velocity for VTI media proposed by Fomel(2004);the timeshift hyperbolic curve approximate equation proposed by Siliqi(2000);the series expansion continued-fraction approximation equation proposed by Thomsen(1994),Alkhalifa and Tsvankin(1995),Hake(1984)that is extensively used nowadays;and the non-hyperbolic approximation formula proposed by Aleixo and Schleicher(2009).After understanding the classical theory,a detailed study is carried out on the method for time domain VTI media anisotropy parameter estimation.Firstly,the root mean square velocity estimation method using data of small offsets(x/z<1)is introduced,and then the equivalent anisotropy parameter ? is estimated using the medium-far offsets(x/z>1)(two-step method);Secondly,the double-parameter root searching method(one-step method)is realized and improved,where an auto-picking algorithm is proposed to solve the problems relatively low resolution and relying on too much manual intervention in the conventional method.The method for parameter estimation on common scatter point gathers(CSP)is proposed to solve the problems of relying largely on the offset ranges and high SNR of seismic data using the above two methods.Finally,the anisotropic high resolution hyperbolic Radon transformation suppression multiple reflection methods and techniques are realized and good results are obtained using the above method in the model data and actual data processing.