The Research Of Prestack Gaussian Beam Depth Migration In Viscous Media

With the development of oil and gas exploration work,the main target of oil and gas exploration is gradually turning to small and complex medium subtle reservoirs,which puts forward higher requirements for seismic exploration technology.As the core part of seismic exploration technology,the importance of seismic data processing technology is self-evident,has always been the focus of geophysics research.Seismic migration imaging method is a key step in seismic data processing.Its main purpose is to realize the spatial homing of the reflection interface and recovery reflection interface space wave field characteristics,amplitude change and reflection coefficient of the reflection interface space to improve the spatial resolution and fidelity of seismic exploration.Meanwhile,seismic migration imaging method can provide good seismic profile for subsequent earthquake interpretation and reservoir prediction work.Conventional seismic migration imaging methods are mostly based on the ideal assumptions of completely elastic,but the viscosity in the real underground media is widespread.If the traditional method based on the completely elastic assumption is used to process the strong viscous seismic datasets,it will lead to the final seismic section of the deep reflection of the weak energy and reduce the imaging resolution,which adversely affects the subsequent interpretation of seismic data and reservoir prediction work.Seismic prestack depth migration technology plays an increasingly important role in the current oil and gas exploration work as an important means for accurate imaging of underground media.For the current massive seismic data,it is necessary to consider the imaging accuracy and computational efficiency of the imaging method in the process of imaging.However,for the general prestack depth migration method,imaging accuracy and computational efficiency are often difficult to achieve simultaneously.The prestack depth migration method commonly used in the industry is Kirchhoff migration method,which has high computational efficiency,but its imaging accuracy is low,and the reverse time migration method with high imaging accuracy is inefficient.As an improved method of ray type migration,Gaussian prestack depth migration method has the advantages of high imaging precision and high computational efficiency,and has high flexibility,so it has high research value and application prospect.In recent years,the research on the Gaussian beam migration method of complex media has been developing rapidly,but most of them have been focused on anisotropic media.The research on the Gaussian beam migration method of viscous media is rare.In this paper,we choose the Gaussian prestack depth migration method as the research object,and the Gaussian prestack depth migration method of viscous medium is developed under the premise of maintaining its computational efficiency,and its application range is further expanded.The main contents of this paper include the following aspects:(1)Based on the traditional Gaussian prestack depth migration method and referring to the one-way wave migration compensation principle,we analyze the influence of the viscous medium on the Gaussian beam complex value travel time.Then,the forward and backward extension wavefields are compensated by correcting the complex value of the Gaussian beam.And the Gaussian prestack depth migration method of the viscous medium is developed by using the cross correlation imaging condition.Combined with the angle information of the Gaussian beam propagation process,the corresponding angle gathers are extracted.Finally,the correctness and validity of the method are verified by the model test.(2)In this paper,we consider the influence of the viscous and anisotropy of the underground medium on the Gaussian beam migration.By modifying the ray tracing equation and correcting the Gaussian beam complex value travel time,the Gaussian beam prestack depth migration method for visco-acoustic VTI media is realized.Then it's validated by model trial.(3)In this paper,based on the elastic wave Gaussian beam migration method,according to the decoupling elastic wave field downward-continuation formula,by correcting the P-wave and S-wave Gaussian beam complex value travel time and then compensate for the P wave and S wave field respectively,we achieve the realization of the viscoelastic medium for the Gaussian beam vector wave prestack depth migration method using cross-correlation imaging condition.(4)In this paper,the optimization algorithm used in the Gaussian prestack depth migration method is briefly introduced,and the selection criteria of the Gaussian beam parameters are given by theoretical analysis and numerical examples.