Navegando por Orientadores "SCHOENBERG, Michael"

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Acesso aberto (Open Access)
Espalhamento elástico em meios anisotrópicos estratificados
(Universidade Federal do Pará, 1994-06-09) PROTÁZIO, João dos Santos; SCHOENBERG, Michael
AVO analysis is an importante tool for extracting lithological information from seismic data using the contrast in acoustic impedance at the lithological boundaries. The isotropic assumption behind this analysis does not hold in many cases. The advent of large offset surveys and multi-component data has revealed the presence of subsurface anisotropy. To interpret such data, the AVO analysis must include anisotropy. This work presents an AVO theory and numerical results for an anisotropic layered medium. This thesis contains three contributions. First, a new approach to the study of reflection-transmission at a plane interface between anisotropic media with a horizontal mirror plane is presented. The Zoeppritz equations are generalized to include anisotropy by the introduction of impedance matrices which greatly simplifies the previous formalisms. Second, the study of the P-wave reflection at an interface between an isotropic and a transversally isotropic medium is described and it is show that the reflected P-wave does not have information about the underlying anisotropic subspace for pre-critical incidence. Finally, the behavior of post-critical reflected and transmitted pulses through a stack of anisotropic layers is discussed. The post-critical pulses are show to carry valuable information on the anisotropy of the structure through which the waves propagate.
Acesso aberto (Open Access)
Modelagem sísmica e inversão na presença de anisotropia
(Universidade Federal do Pará, 1993-11-04) COSTA, Jessé Carvalho; SCHOENBERG, Michael
The assumption of anisotropic elastic models, in the context of exploration seismology, has been increasing since the advent of new aquisition tecniques: VSP, walkway VSP, crosshole tomography and large offset seismic surveys. Effective anisotropic elastic models can account for patterns of inhomogeneities at a scale much lower than the wavelength of the propagating seismic energy. Particularly, effective media can account for the most robust seismic data, i.e., traveltime measurements. This work investigates some aspects of wave propagation, raytracing and traveltime inversion in anisotropic media. The propagation of SH waves in a layered anisotropic medium in the most general case where these waves can occur, i.e., propagation in the mirror symmetry plane of a monoclinic medium, is studied. It is shown that SH reflected field from a stratified half-space is 'blind' to the possible anisotropy below. Fast ray tracing procedures for stratified anisotropic media in 3D are presented. Such ray tracing codes are a first step towards the development of traveltime inversion algorithms for non-flat anisotropic layers in 3D. Traveltime inversion of VSP and walkway VSP is a promissing approach to 3D velocity model building, starting from a well location. These velocity models are necessary for the migration of seismic data in the presence of anisotropy. The analysis of the nonlinear tomographic inversion, for a vertically inhomogeneous transversally isotropic medium with vertical axis of symmetry (TIV), is presented. The limitations of qP traveltime data are pointed as well as the consequences of the lack of full angular ray coverage for tomographic inversion. An algorithm for tomographic inversion is presented and evaluated in synthetic data seis. Application to real data is presented. This approach is attractive for cases where the formations are known a priori to be relatively flat, and where crosswell data itself shows a high degree of left-right symmetry. It also may be of use for preliminary surveys, where the layered estimate can be used as a background model to carry out more detailed analysis, e.g., as an anisotropic velocity model for migration, or as a calibration model for AVO analysis.