Research On The Method Of The 3-D VSP Multiwave Ray Tracing Forward Modeling

Research on the seismic waves's propagation plays an important role ingeophysics exploration. Until now the seismic ray method has been used in manyaspects of the seismic prospecting. For example, the method is used to calculate theseismic wavefield in 3D isotropic and anisotropic medium. Seismic ray method canalso solve some complicated forward and inversion problems of transverse anisotropymedium in the field of seismology and exploration activity. This paper mainly studythe segmentally-iterative ray tracing forward and Gaussian beam forward modeling.From the Eikonal equation, this paper study iteration segment by segment raytracing that can adapt to 3D VSP any complex layered media. This method is based onSnell theorem and Fermat's principle and only .The main idea is by use of one-orderTaylor incomplete expansion to expand Travel time equation, and ignore the secondentry point to get a computational reflection (transmission point) formula. Startingfrom an arbitrary given initial ray path, ray-t racing is iteratively calculated segmentby segment. The procedure is kept on until the sum of adjustment quantity in thewhole path is in the range of precision. Formula contains only include add, subtract,multiply, divide calculated to improve the computational efficiency.In complex multi-layered media three-dimensional inclined VSP forwardray-tracing, through the horizontally layered model, tilted layered model and arandom fluctuation layered media model modeling, iteration segment by segment torealize 3-D deviated well VSP ray tracing in the application of results.Ray methods Play a vital role in seismic exploration .Among all ray methods,Gaussian beam method is a fast method of seismic wave field modeling .The seismicwave field obtained by this method has wave properties in both kinematics andhigh-frequency dynamic. By merging wave equation with the ray theory,the method obtains ray tracks by the kinematical ray tracing,and obtains distributions ofhigh-frequency by the dynamic ray tracing . As a result,it costs little calculation time,and shows good precision.Finally I give out several numerical examples of typical model to syntheticseismogram with Gaussian beam. Its purpose is to analyze the characteristics ofGaussian beam and to reflect the applicability of gaussian beam forward modeling.