Research On Gaussian Beam Migration Method Based On Attenuation Compensation

Gaussian beam migration is an elegant and efficient depth migration method with accuracy comparable to the wave-equation migration and flexibility comparable to the Kirchhoff migration.The viscosity of subsurface media cause amplitude attenuation and phase distortion of seismic waves,which decrease the seismic data resolution and imaging precision.The paper aims for compensating the seismic wave absorption in viscoelastic media,and improving the resolution of seismic imaging,especially in deep section.It is concerned with systematic study of attenuation compensation with Gaussian beam methods.In order to simulate the wave propagation in a viscoelastic medium using Gaussian beam,we introduce the complex velocity Q(quality factor)-related and exact viscoelastic Zoeppritz equation based on the elastic Gaussian beam concept.To compensate for attenuation of seismic records,first,we based on Gaussian beam migration algorithms operating on common-shot gathers,derive expressions about attenuation and compensation and correct amplitude attenuation and phase distortion caused by Q to implement Q-compensated Gaussian beam migration.Numerical test and real data show that this method compensates for deep reflection energy effectively,improve the quality of migration image.Afterthat,we synthesize direct wavefield and backward wavefield using Green function,realize Gaussian beam reverse-time migration(GBRTM)based on the cross-correlation imaging condition.Then,introduce the Q-related absorption(compensation)on the basis of GBRTM,compare Green’s functions’ accuracy between Gaussian beam wave field and frequency domain wave equation forward,given compensation principles and compensation processes,and implement Q-compensated Gaussian beam reverse-time migration.The Q-compensated GBRTM compensate for the energy loss in direct wavefield and backward wavefield simultaneously,and correct the complex traveltime.Numerical examples indicate the accuracy of Q-compensated GBRTM is close to that of Q-compensated wave equation reverse-time migration(WERTM).PP-and PS-wave data can both be obtained in multicomponent seismic exploration.Compared with pure PP-wave,the PS-wave carries different information of target area in subsurface,which can provide more physical parameters and improve the accuracy of seismic prospecting.Therefore,in order to make full use of multicomponent seismic data,we propose the attenuation-compensated multicomponent Gaussian beam migration and the attenuation-compensated multicomponent GBRTM.First,the wavefield is decomposed into PP-and PS-wave,then,do migration based on the scalar acoustic wave equation.The purpose is to provide a new and effective multi-component data imaging technique,compensating the attenuation effect of multi-component seismic records simultaneously.Numerical simulations suggest that the two approaches both improve the imaging precision and resolution for multicomponent seismic data,especially for highly attenuating geological environment.