Angle Domain Common Image Gathers Based On Reverse-time Migration In TI Media

In recent years,seismic exploration targets have become increasingly complex,and the accuracy of seismic exploration technology has become increasingly demanding.Based on the full wave equation,the RTM can deal with wave propagation in all direction without angle limitation.The imaging precision of RTM is high,it can handle not only multi-arrivals,but also overturned reflections.The anisotropy exists in the earth medium generally,and the TI medium is one of the most common in sedimentary rocks.The research on anisotropy has become a hot topic in the context of the current seismic exploration towards high precision.The traditional isotropic RTM method has great limitations in the imaging of complex media.Therefore,the development of the anisotropic reverse-time migration method is very meaningful.The inverse time migration method is very sensitive to the initial velocity model.The inaccuracy of the initial velocity model greatly affects the imaging accuracy.As an important output of RTM method,the angle-domain common-image gathers,can provide velocity information and amplitude information for velocity analysis and AVA.Accurate velocity model can be obtained by performing velocity inversion by angular gathers.The Poynting vector method is a fast and efficient method for extracting angle gathers.The method requires less storage and calculation,and the obtained angle gathers have higher resolution.The ADCIGs also has higher resolution than other methods.In this paper,firstly,on the basis of acoustic approximation,the first-order qP-wave equations of different forms of VTI media are deduced from the basic theory of elastic waves and dispersion relations,and then the equations are generalized to TTI media according to the coordinate transformation relationship.In order to improve the stability of the equation,the physical parameters were introduced on the basis of previous studies,and the first-order stress-velocity qP wave equation in a stable TTI medium was deduced.In order to facilitate the study of anisotropic chromatography and velocity inversion methods,different angle gather extraction methods have been studied.This paper focuses on Poynting vector-based angle gathers extraction method,the superiority of angle-domain imaging conditions in suppressing low-frequency noise is analyzed.Triangular filter is optimized for diagonal gather,which is smooth and smooth.Finally,the anisotropic model was calculated to verify the stability of the method.The comparison between anisotropic and isotropic angle gathers shows that the method is effective and necessary.