Study Of Wave Equation Based Seismic Illumination Modeling And Seismic Observation System Optimization Design

In the dual-complexity area, the effects of focusing, defocusing and high-velocity layers lead to seismic data with low signal-to-noise ratio and poor migration. Seismic illumination analysis technology is a kind of model based analysis technology which can be used to study the distribution of seismic amplitude or wave-field in the target area. Seismic illumination can obtain not only the distribution of seismic wave-field generated by seismic source, namely unidirectional illumination, but also the bidirectional illumination which can represents the source excitation effect and Geophone receiving effect. So seismic illumination analysis based optimal seismic observation system design will improve the detectivity of seismic layout for better imaging. Although a lot of scholars at home and abroad have done a mountain of work on seismic illuminaton analysis technology, so far there is yet no an unified cognition and application standards about seismic illumination whose industrial application effect and acceptance are uneven. Seismic illumination has gradually turned into wave equation theory era from ray tracing theory era. One-way wave equation based seismic illumination can not satisfy the highly complex region. In contrast, full-way wave equation with high simulation precision, abundant wave-field information, no angle limitation and other advantages can adapt any complex area. Therefore full-way wave equation based seismic illumination analysis technology has great application prospect.On the basis of previous study, begin with the basic principle and concept of seismic illumination, the major existing seismic illumination functions were systematically summarized, and a number of classification standards were introduced. Further more, any seismic illumination functions can be assigned to two categories, namely of unidirectional illumination only considering source or receiver and bidirectional illumination taking both source and receiver. According to the seismic wave theory, One-way wave equation and full-way wave equation were deduced. In addition, their numerical modeling method were studied in detail. This is the basis of approach to study of wave equation based seismic illumination analysis technology. The numerical simulation results show that the defects in one-way wave equtation result in inaccurate seismic illumination energy, especially in subsalt area with strong scattering loss. Though full-way wave equation can obtain more accurate seismic illumination energy, there could are some interference patterns caused by the interaction between upgoing and downgoing wave-field misleading the seismic illumination analysis. For this reason, Poynting Vector was applied to seperate the full-way wave equation based seismic wavefield into reflection wavefield only containing upgoing waves and incident wavefield only containing downgoing waves. Then two new seismic illumination functions were developed, namely of incident illumination and reflection illumination. The numerical simulation results proved that the Poynting Vector based wavefield decomposition method is correct, and the incident illumination can describe the distribution characteristics of downgoing wavefield better than full-way wave equation based unidirectional illumination. One-way wave equation based bidirectional illumination was improved, including XIE-WU bidirectional illumination and DUC-DC bidirectional illumination. The improved bidrectional illumination methods not only enhance accuracy of bidirectional illumiantion, but also break through the defect of XIE-WU bidirectional illumination which can not satisfy the fact that geophones at different places should receive different wavefields. Moreover, the double focus theory based double focus illumination analysis tecnology was taken into this research and a geometry prestack migration resolution function was proposed. In the end, the study of seismic layout optimal design using wave equation based seismic illumination was carried out, achieving the optimization of target-oriented source or receiver surface area, the seismic wave focus direction design of array source in infill area, the parameter optimization of seismic layout meeting the need of prestack migration resolution.