Study On Multiwave And Multicomponent Reverse Time Migration

Reverse time migration is based on two-way wave equations to extrapolate the wavefield.It has no dip restriction and can applied to image complex structural areas.It is one of the most accurate imaging method at present.Multiwave and multicomponent seismic data contain more P-wave and S-wave information.Making full use of multiwave and multicomponent seismic data can get more information about underground structure and lithology,and improve the accuracy of seismic exploration.Multiwave and multicomponent reverse time migration can better image complex structures and identify special structures related to fluids.However,there are some problems during implement of multiwave and multicomponent reverse time migration,such as crosstalk noise between different wavefield,low resolution and polarity reversal problem of converted wave and so on.To solve these problems,this paper intensive studies multiwave and multicomponent reverse time migration method based on previous studies.In this paper,this paper mainly does the following work:1)This paper studies staggered grid finite difference numerical simulation for elastic wave equations in isotropic media and VTI media.2)This paper systematically studies the principle,workflow and key problems of isotropic elastic reverse time migration.And this paper studies multiwave and multicomponent reverse time migration based on decoupled equations in isotropic media.The P-wave and S-wave can be decomposed quickly by decoupled equations,and then the vector P-wave and S-wave can be used to image to suppress the crosstalk noise and improve the imaging quality.The polarity reversal of converted wave is well corrected by the vector imaging condition.In addition,this paper also study the elastic reverse time migration method based on the excitation amplitude imaging condition,which can save memory cost and improve computational efficiency.3)This paper studies elastic reverse time migration of VTI media.The influence of anisotropy is well corrected by elastic reverse time migration of VTI media.Because it is difficult to separation the elastic wavefield in anisotropic media,this paper proposes a wavefield separation method in anisotropic media which is based on pseudo-acoustic equations.And this paper further proposed an elastic reverse time migration method in VTI media based on pseudo-acoustic equation.Vector P-wave and S-wave in VTI media are obtained by the new method to suppress the crosstalk noise and improve imaging quality.The polarity reversal of converted wave is well corrected by the vector imaging condition.In addition,this paper also studies the elstic reverse time migration in VTI media based on the excitation amplitude imaging condition.4)This paper systematically studies the principle and optimization algorithm of least squares migration.And this paper introduces the elastic least-squares reverse time migration in isotropic media in detail and achieves this method.Through the analysis of radiation patterns for different kinds of source,this paper found there exists serious crosstalk noise between different wave modes.In order to suppress crosstalk noise,this paper proposes elastic least-squares reverse time migration based on wave mode decomposition and also proposes decoupled adjoint state equations.Furthermore,this paper proposes new gradients equations based on wave mode decomposition to update the P-and S-wave images.The proposed new elastic least-squares reverse time migration can suppress crosstalk noise between different waves and improve imaging quality.5)This paper proposes elastic least-squares reverse time migration in VTI medium.The new elastic least squares reverse time migration method can better correct the influence of anisotropy and improve the migration imaging quality.