Research Of Shortest Path Ray-Tracing And Travel-Time Tomography In TI Media

With the increasing demand for oil and gas resources in the world economy,the requirements for seismic exploration's accuracy are becoming higher and higher.Conventional pre-stack depth migration and velocity modeling method based on isotropic assumption can no longer meet the high requirements for the imaging of complex underground structures.As one of the most effective methods in seismic data processing,the travel time tomographic method is widely used in field static correction,velocity modeling,and neglecting the existence of underground anisotropy will influence the accuracy of static correction and migration imaging quality.Therefore,it is of great significance to carry out the anisotropy travel time tomographic method.The method of travel time tomographic method is mainly composed of two parts,the first is forward modelling.In this paper,we derive the elastic wave equation of the general heterogeneous medium under the assumption of linear elastic medium,and obtain the phase velocity and group velocity in TI media by solving the Christoffel equation.Then we use the shortest path ray tracing algorithm to calculate the travel time and the ray path under the assumption of anisotropy.During the algorithm implementation process we use the Newton's method to solve the phase velocity accurately and by introducing the secondary node we get the efficiency improved.In aspects of inversion: On the basis of ray tracing algorithm,we deduce the ray tomography equation in TI medium,and introduce the corresponding regularization method and LSQR algorithm to optimize the equations solving process.Through the analysis of the sensitivity of TI medium parameters we formulate the Inversion strategy.Finally,through the model test we demonstrate the correctness and validity of this method.