Method And Technology For Angle Domain Reverse Time Migration

RTM is widely evoked because it can handle multiple,turning wave,lateral velocity varied,large step dip and overhang structure.Characteristics of seismic wave in angle-domain processing such as reflection,scattering ect.can be used to image,illumination analysis,image correction,AVA and MVA.The thesis works on imaging in angle domain and corresponding problems.1.The mechanism of low wave-number in RTM is analyzed based on conventional RTM principle.People pay attention to the angle-domain method because procedure in angle-domain can truly reflect the influence of different wave during imaging.In order to improve angle decomposition efficiency,Poynting vector method is adopted,and local image matrix is constructed to analyze the influence of different wave during imaging.The low wave-number noise is removed by angle filter.2.ADCIG based on two-way wave equation is the gathers which is considered that no kinematics and dynamics false,more sensitive to migration velocity and reflect truly AVA of subsurface.A efficient ADCIG extraction method based on Poynting vector is discussed,and the numerical result is demonstrated.3.Seismic illumination technique can provide quantitative analysis for the imaging effective from acquisition aperture,complex overburden and target dip angle ect.Poynting vector is used to decompose source and receiver wave-fields in the thesis,according to which construct local illumination matrix.The local illumination matrix is a basis for angle-domain illumination analysis,which composes all the possible incident and scattering wave influence.The different illumination description and acquisition dip response of subsurface can be obtained by the interaction between incident/scattering wave in angle domain and reflectors.The numerical calculation is worked on SEG model and local illumination and ADR is calculated based on local illumination matrix.4.The migration image is a distorted image because of acquisition aperture,complex overburden and target dip angle ect.RTM imaging resolution and correction is discussed.Several amplitude correction methods are compared,which demonstrate that correction in dipangle domain has the best effect.By analyzing the mathematical process during imaging and the distorted factor,point scattering function(PSF)is introduced.According to the relation between PSF and ADR,the raw RTM image can be corrected by ADR in dip angle domain,which not only compensates the image amplitude,but also improves image quality,imaging noise is restrained to some extend.In addition,it is assumed that the illumination contribution for a dipping angle is equivalent,PSF deconvolutional compensation considers not only the dipping effective,but also the scattering strength for different direction,so the compensation effevitive is better.By embedded disturbing points in the model to compute PSF,the PSF deconvolution improves the imaging quality effevitvely.