Research On The Elastic Wave Least Squares Reverse Time Migration

With the increasing complexity of the oil and gas exploration field,the requirements for seismic data imaging accuracy have also increased significantly.Elastic wave RTM(reverse time migration)can make full use of the wavefield information in multi-component seismic data to achieve accurate imaging of underground structures.On this basis,combined with the inversion idea,elastic wave least squares RTM method is implemented to improve the imaging resolution,which is beneficial to oil and gas exploration and development deployment.This paper focuses on the study of elastic wave least squares RTM.First,based on the first-order velocity-stress equation,high-precision staggered grid finite difference method is used to realize elastic wavefield numerical simulation.In order to extract the P wave and S wave,discuss the wavefield decomposition method based on Helmholtz decomposition,decoupling equation,and wavefield decomposition method in the wavenumber domain.Furthermore,the decomposition effect and calculation efficiency of them are compared and analyzed.According to different wavefield decomposition methods,cross-correlation imaging condition,inner product imaging condition,and excitation amplitude imaging condition are used to image the structure respectively.For the polarity reversal phenomenon in imaging results,an energy norm imaging condition is used for imaging.Model tests prove that the imaging condition effectively avoids polarity reversal phenomenon.In order to correct the polarity reversal phenomenon in cross-correlation PS imaging,a common shot domain polarity correction method is adopted.For the polarity reversal phenomenon produced by inner product PP imaging and excitation amplitude PP imaging,P-wave stress imaging is used as the supplement of imaging.In the imaging process,effective boundary storage strategy for source wavefield reconstruction is used to reduce storage burden.In order to improve the quality of imaging profile,on the basis of elastic wave RTM,derive the de-migration operator and adjoint operator,establish the misfit function,and use the conjugate gradient method to iteratively optimize the calculation,thereby achieving the elastic wave least squares RTM method.Model tests show that elastic wave least squares RTM can effectively suppress crosstalk,improve the lighting range,and obtain underground reflectivity results with high-resolution and balanced amplitude.