Research On Viscoelastic Least-squares Reverse Time Migration Imaging

With the development of seismic exploration,the contradiction between deepening and complicating of exploration targets and functional limitations of conventional imaging methods is getting more and more acute,and the demand for high-precision imaging methods for complex structures is growing.Compared with the traditional methods such as one-way wave migration method and ray migration method,the reverse-time migration method has the advantage of imaging complex structures because of the introduction of two-way wave equation,Now the reverse-time migration method has been widely used.Because of the viscosity in the real underground media,the amplitude attenuation and phase distortion will occur when the seismic wave propagates in the media.The inverse time migration imaging method based on acoustic and elastic wave will form the fuzzy imaging results,even the wrong phase.Therefore,in order to improve the accuracy,resolution and fidelity of seismic imaging,the least square inverse time migration imaging method of viscoelastic wave for seismic data is studied in depth.And the main achievements are as follows:?1?Based on the finite difference numerical simulation method,the forward modeling of acoustic wave,viscoacouctic wave,elastic wave and viscoelastic wave equation was realized.Simulated the seismic wave field with layered model and Salt velocity model,The results show that Viscoelastic wavefield simulation approach entirely considers the vector characteristics of seismic wave propagation and attenuation effects of the subsurface,which is well consistent with wave propagation in subsurface structures with attenuation.?2?Study of reverse time migration imaging,made a deep study of absorption boundary condition,wave field reconstruction,noise treatment.?3?Propose a stained wavefield inverse optimization method to improve the imaging quality of the target area and the occlusion area of salt model,in which the stained area is imaged clearly.?4?The least square reverse time migration method was studied,and the accurate imaging of underground structure velocity disturbance was realized;Derive the forward operator and adjoint operator of acoustic,viscoacoustic and elastic LSRTM,and realize LSRTM for prestack seismic data,which can effectively suppress migration artifacts and improves the image quality of seismic data.?5?The viscoelastic wave least square inverse time migration method is developed.Aiming at the characteristics of amplitude matching of L₂ objective function,a zero-delay cross-correlation objective function based viscoelastic wave least square inverse time migration method is studied.Apply a pseudo-analytic step method to image the multicomponent seismic data with strong attenuation.Numerical examples have shown that the proposed method is insensitive to the amplitude errors and can provide improved image quality.?6?To provide an accurate background velocity model for proposed viscoelastic LSRTM approach,an exploratory study on the viscoelastic full waveform inversion?FWI?is carried out.A Marmousi-2 model example has shown that viscoelastic FWI can improve the reconstruction accuracy of P-and S-wave velocity by incorporating the P-and S-attenuation parameters.Compared with the conventional elastic FWI,viscoelastic FWI has faster convergence rate and higher inversion precision.