Study On Seismic Forward Modelling Of Simulated Prestack Depth Migration

Seismic pre-stack depth migration is a key technology for depict the underground structure and reflectivity information.To obtain migration imaging results,seismic acquisition or forward modeling,conventional processing and migration processing are required.However,forward modeling and migration imaging still have many problems in practical application,such as large amount of calculation and long running period,and the conventional processing and migration process is complicated.In order to obtain theoretical imaging results efficiently,and avoid a series of cumbersome processes such as forward modeling,conventional processing and migration,a novel forward modeling method for simulating pre-stack depth migration imaging is developed in this paper.In this method,the source information,observation system parameters and ray path information are directly used to construct the point spread operator without forward modeling and migration processing,and according to the velocity model and reflectivity information,the theoretical imaging results are generated.The method is simple,efficient and accurate.The imaging results can quickly detect the problems existing in the observation system and the quality of seismic data,provide reference for optimizing the parameters of the observation system and evaluating the imaging quality,provide evidence for seismic interpretation,and meet the research needs of acquisition,processing and reservoir interpretation.Since the simulated imaging method in this paper can be used as the evaluation standard of imaging method,combined with the background of the increasing difficulty and requirements of exploration and the increasing demand for complex structures and amplitude preserving imaging,in this paper,novel reverse-time migration and least square reverse-time migration based on meshfree finite difference are developed.The meshfree imaging methods have an important characteristic that it can calculate the velocity model with arbitrary irregular shape,so that it can be directly applied to the imaging of velocity model with rugged topography,which overcomes the restriction for seismic exploration in complex surface areas.In comparison of meshfree and traditional regular-grids imaging methods,it can be found that the meshfree method can better depict the underground structure with fewer discrete elements,especially the curved and steep interface.The meshfree imaging method can not only save computational memory,but also provide higher precision imaging result for seismic exploration.In addition,the principle of simulated imaging method and how to construct imaging operator quickly by ray tracing is expounded in detail.In the imaging operator analysis,it can be found that with the increase of depth,the spectral bandwidth of the imaging operator becomes narrower,the wavelength becomes longer,and the imaging resolution represented by the operator gradually decreases,which conforms to the actual law.Finally,several numerical examples are used to introduce the application of simulated imaging method in evaluating imaging quality,guiding the establishment of field observation system and assisting the research of depth domain inversion methods.The practicability and convenience of the method in this paper are verified.