High Quality Seismic Imaging Algorithm For Complex Media And Its Quality Control

Reflection migration is an important processing technique for detecting the sub-surface structure in oil and gas exploration. High quality seismic image depends not only on high quality seismic data and advanced migration method but also on accurate migration velocity model. This thesis focuses on improving the quality of seismic im-age in complex media. It includes improvement for image quality in shadow zone of the salt body, the correction for the image distortion, the influence of the near surface heterogeneities to the image quality and the improvement for one-way propagator.Due to limited acquisition aperture, complex overburden structure and target dip-ping angle, the migration often generates a distorted subsurface image. In this thesis, the staining algorithm is proposed to mark the subsurface target structure and obtain the seismic wavefield and data related to it. Applied to seismic modeling, this method can track the propagation of the wavefield and obtain the data related to the labeled target structure. In seismic migration, this method can image the target structure, especially those in the weak illuminated zone, exclusively so as to improve the image quality. When the marked target structure shrinks to a single scattering point, the pure scattered data from this scattering point can be obtained by using the staining algorithm. The point spreading function (PSF) can be calculated by imaging the scattering point using the scattered data. Illumination information for a given velocity model and acquisition geometry can be extracted from the PSF or its wavenumber spectra. By deconvolving the PSF from the original depth image, the biased image due to the joint effect of uneven illumination, complex subsurface structure and reflector dip angle can be corrected. The parameterized random media are used to characterize the near surface small-scale het-erogeneities. The PSF is used to investigate the relation of near surface small-scale heterogeneities and the seismic image quality.A hybrid acoustic one-way, one-return propagator for blocked inhomogeneous me-dia is also developed. Based on De Wolf approximation, the method combines tradi-tional one-way propagator and boundary element method. It calculates the free propaga-tion, boundary scattering and the volume scattering due to weak heterogeneities in each thin-slab, which together contribute to the total wavefield at the slab exit. This approach can overcome the limitation and difficulty of the traditional perturbative method.