Research On The 2D Acoustic And Elastic Wave Prestack Reverse Time Migration Imaging Methods

Reverse time migration(RTM)is an important method for complex structure imaging,which is also the research focus in recent years.Conventional RTM method for acoustic wave has satisfactory results,and has been widely applied in industry.RTM for elastic wave attracts more attention due to the raising requirements for imaging precision.However,implementing conventional cross-correlation imaging condition in elastic wave RTM could induce polarity reversal problem,which influences the imaging accuracy.This paper introduces research on several aspects including numerical simulation,wavefield decomposition,imaging condition and denoising aiming at increasing the imaging accuracy and calculation efficiency of elastic wave.In the aspect of numerical simulation,the factors influencing dispersion are analyzed.It is testified that optimal staggered-grid finite difference scheme has higher precision than the Taylor expansion method.Based on the research before,the optimized time evolution scheme in 3D is derived.In the aspect of wavefield decomposition,research on two kinds of elastic wave equations including decoupled elastic wave and velocity-dilatation-curl equation is conducted,which could obtain vector elastic wavefield.In the aspect of imaging condition,inner product imaging condition is applied,which could avoid polarity reversal.A fast imaging scheme is proposed to reduce calculation cost and storage requirement.In the aspect of denoising,Laplace filering and wavefield separation methods are introduced.