Research On Nonlinear Velocity Inversion Method Based On Seismic Full Wavefield Information

With the deepening of the oil and gas exploration and development,complex reservoirs have become the focus of exploration and development.However the structure and lithology of these reservoirs are more complex than conventional reservoirs,which requires us to obtain high precision velocity model of underground geological structures.Compared with other conventional velocity analysis method,the nonlinear velocity inversion method based on seismic full-waveform makes full use of the kinematics and dynamics information of seismic wave during the propagation process,so that the velocity information of complex geological structures can be accurately obtained.This paper has thoroughly studied the nonlinear velocity inversion method based on seismic full-waveform information on the basis of predecessors’ research,and realized complete process of nonlinear velocity inversion.Specific research work is as follows:1)Dispersion problem,stability conditions,boundary conditions in the process of forward simulation are analyzed in detail.With the quantitative analysis of the dispersion problem in the forward modeling process,we can get more reasonable parameters,so as to improve the efficiency of our inversion.The validity of the forward modeling method is verified by the model test.2)Continuous and discrete gradient calculation formula of nonlinear waveform inversion method based on gradient method is derived in detail,then we give the specific process of nonlinear velocity inversion.3)We adopt multigrid method to optimize local extremum problems in wavefom inversion process;how to choose the appropriate frequency are discussed in detail in the process of using multigrid method.4)Finally,a complete nonlinear velocity inversion algorithm is implemented by C language programming,whose testing result shows the effectivity of simple models and complex models,which also comfirmed it’s validity and correctness.