VTI介质单程波叠前深度偏移方法研究

发布时间：2018-05-27 06:09

本文选题：叠前深度偏移 + VTI介质　；参考：《长安大学》2017年硕士论文

【摘要】：随着现今油气勘探中勘探目标的日趋复杂,以往基于各向同性简单介质基本假设的基本成像理论越来越不能满足现阶段油气勘探的实际需求,这就使得研究符合地下实际地质模型的复杂介质的成像方法变得非常迫切。另一方面,各向异性普遍存在于地壳介质,因此在现阶段的地球物理研究中,开展地震各向异性的研究对于认知地球内部构造、油气田的勘探与开发以及地质灾害防治等方面都具有重要意义。基于各向异性介质的叠前深度偏移技术是现阶段对复杂地质情况成像效果最好的技术。在复杂构造区和更深部的地震勘探中应用叠前深度偏移技术,可以获得较为精细的成像效果。论文首先对各向同性介质声波方程进行单程波解耦,获得可直接进行波场上、下外推的单程波延拓算子。针对复杂介质,对延拓过程中的垂向波数利用不同的数学展开式进行近似展开,分别推导出裂步傅里叶(SSF)、广义屏(GSP)与切比雪夫傅里叶(CF)波场传播算子。针对VTI介质,结合地震叠前深度偏移的基本理论以及波场在VTI介质中传播的频散特性,分别推导了可适用于VTI介质的SSF、GSP、CF延拓算子。然后对比分析这三种算子的相对误差曲线和脉冲响应特征,总结了它们的优缺点。再借助于偏移成像理论,编程实现完整的VTI介质单程波叠前深度偏移。最后利用SEG VTI-HESS模型验证这三种偏移方法的成像效果及成像效率。对比分析裂步傅里叶(SSF)、广义屏(GSP)与切比雪夫傅里叶(CF)波场传播算子的相对误差、脉冲响应效果,对于横向速度差异较大、大倾角的介质,SSF算子将产生较大的误差,GSP算子效果优于SSF算子,CF算子误差最小、脉冲响应也更符合实际的波场传播过程。理论模型试算结果表明:要在复杂介质区获得较好、较精细的成像效果时,应选择切比雪夫傅里叶叠前深度偏移方法;在构造相对简单的地质区域,选择裂步傅里叶偏移方法可以大大节约计算成本;广义屏方法的效果是这两种偏移方法的一个折中。
[Abstract]:With the increasing complexity of exploration targets in the present oil and gas exploration, the basic imaging theory based on the basic assumption of isotropic simple medium is more and more unable to meet the actual demand of oil and gas exploration at the present stage. This makes it very urgent to study the imaging methods of complex media in accordance with the actual underground geological model. On the other hand, anisotropy exists generally in crustal media, so in the present geophysical research, the study of seismic anisotropy is of great importance to the cognition of the inner structure of the earth. The exploration and development of oil and gas fields and the prevention of geological disasters are of great significance. Prestack depth migration based on anisotropic media is the best technique for imaging complex geological conditions at present. The application of prestack depth migration technique in the seismic exploration of complex structural areas and deeper areas can obtain more precise imaging results. In this paper, we first decouple the acoustic wave equation of isotropic medium by one-pass wave decoupling, and obtain the one-pass wave extension operator which can be extrapolated directly from the wave field. For complex media, the vertical wavenumber in the extension process is approximated by different mathematical expansions, and the wave field propagation operators are derived, respectively, for the split-step Fourier transform (SSF) and the Chebyshev Fourier transform (CFF). For VTI medium, combined with the basic theory of seismic prestack depth migration and the dispersion characteristics of wave field propagating in VTI medium, the VTI GSP CF continuation operator suitable for VTI medium is derived respectively. Then, the relative error curves and impulse response characteristics of these three operators are analyzed, and their advantages and disadvantages are summarized. With the help of migration imaging theory, complete VTI medium prestack depth migration is realized by programming. Finally, the SEG VTI-HESS model is used to verify the imaging effect and efficiency of the three migration methods. By comparing and analyzing the relative errors of the propagation operators of split step Fourier transform (SSF), generalized screen (GSPs) and Chebyshev Fourier transform (CFD), the effect of pulse response is quite different for transverse velocity. The effect of SSF operator is better than that of SSF operator and the impulse response is more consistent with the actual wave field propagation process. The experimental results of theoretical model show that the Chebyshev Fourier prestack depth migration method should be chosen in order to obtain better and more precise imaging effect in complex media regions, and in geological areas with relatively simple structure, the method of Chebyshev Fourier prestack depth migration should be selected. The computational cost can be greatly saved by choosing the split step Fourier migration method, and the effect of the generalized screen method is a compromise between the two migration methods.
【学位授予单位】：长安大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：P631.4

【参考文献】