Application Of Reverse Time Migration Method In Anisotropic Viscous Media

At the stage of oil development,the exploration and development objects we face d are becoming more and more complex,mainly based on the discovery and understa nding of complex structures,thin interbedded reservoirs and concealed reservoirs.How ever,the current conventional seismic data imaging accuracy can no longer meet the r equirements of fine detail.It needs more high-resolution and high-precision seismic im aging technology to greatly improve the resolution capability of seismic data for small-scale geological bodies,and provide technical support for the development of fine ex ploration and development in the middle and later stages.The two-way wave inverse time migration imaging technology based on wave propagation extension provides the basis for the joint imaging of three different frequency bands and different observatio n methods for cross-hole seismic,VSP and ground seismic.On the basis of extracting the effective seismic wave field,the forward continuation source wave field and the reverse continuation shot collection record the wave field,and then imaging conditions are used to extract the imaging values.Joint imaging can not only maintain the adv antages of ground seismic imaging for the main underground structures and formation interfaces,but also combine the advantages of cross-well seismic between micro-ampl itude structures and thin interbeds,and effectively improve the vertical and horizontal resolution of seismic data.Solving the problem of insufficient resolution of seismic da ta opens up new technological approaches.The actual underground medium encountered in seismic exploration is generally v iscous.The seismic wave passes through the underground stratum.Even if the attenua tion caused by transmission loss,geometrical diffusion and other factors are compensated,the deep energy is still weaker than the shallow layer.Based on the above theor etical analysis,in order to improve the imaging effect and realize the amplitude-preser ving migration imaging,this paper is based on the theory of visco-acoustic medium o f the standard linear solid viscoelastic mechanism model to realize the reverse-time de pth migration of the visco-acoustic medium and the visco-acoustic medium.Combinin g the reverse time migration with the least squares idea,the least squares LSRTM of the viscoelastic medium with amplitude compensation is developed.The trial results of the model data are good.It is verified that the reverse-time migration and the leas t squares offset of the visco-acoustic medium can compensate the absorption attenuatio n of the seismic wave by the viscoelastic medium,and the amplitude-preserving imagi ng can be performed.In each iteration of the traditional LSRTM,three forward or re verse modeling is required.The calculation cost of the forward modeling based on th e linear wave equation is twice that of the conventional forward modeling.Therefore,the computational cost of N iterations of LSRTM is 2.5N times that of traditional R TM.The high computational cost makes this method unusable for large 2D and 3D models.Whether it is LSRTM or traditional RTM,their computational cost is related to the number of shots.Similar to the plane wave offset,multiple shot gathers can b e encoded into a super gather by phase encoding techniques.Using super gathers can reduce the amount of computation and cost effectiveness.