【作者】 张晓明；

【导师】 何兵寿；

【作者基本信息】 中国海洋大学 ， 地球探测与信息技术， 2010， 硕士

【摘要】 与通常地面激发地震波,地面接收所得的地面地震剖面不同,VSP是在地面激发,在沿井孔不同的深度处接收所得。由于它是通过观测波场在垂直方向的分布来研究地质剖面的垂向变化,因此,波的运动学和动力学特征更加明显。与地面地震相比,VSP资料不但分辨率高,性噪比高,而且还可以同时记录上行波和下行波,可以为地面地震资料处理和解释提供较为精确的时深转换以及速度模型,可靠的识别地震反射层的地质层位,进行层位标定。在VSP资料中提取出的较纯的地震子波可以用于对地面地震资料的反褶积,提高地面地震资料的分辨率。非零井源距VSP还可以对井周围和远离井的地层构造进行较高垂向和横向分辨率的成像,通过对VSP资料中纵波和转换波的研究可以有效的求取地层岩性参数变化情况。本文的主要内容主要围绕非零井源距VSP的成像处理展开。地震正演模拟是一种十分有效的地震资料处理辅助手段,弹性波方程能全面准确地描述地震波的动力学特征和运动学特征,对非零井源距VSP弹性波方程做正演模拟,是了解地下介质中弹性波场特征和传播规律的一种重要方法,借此设计和制定更合理的处理方法和流程。在交错网格中对方程进行差分离散,推导出弹性波方程的二阶时间差分精度、高阶空间差分精度有限差分格式；采用完全匹配层(PML)吸收边界条件来解决截断边界处外行波的反射问题,通过数值计算得到高精度的合成记录。非零井源距VSP三分量观测中所记录的波场十分复杂,既有上,下行纵波,又有上,下行转换波等。各种波场往往交互混杂在一起,给分离工作带来很大的不便。本文根据三分量VSP记录中波的偏振特性和视速度特性制定出一种两步法来进行波场分离。首先通过基于角度扫描的偏振滤波,将原始记录中的复杂波场分离成为简单波场,再对简单波场进行视速度滤波,分离上下行波场,从而实现各种波的分离。利用VSP资料反演地震层速度具有相当大的优势,因为VSP资料包含有丰富的地震波速度信息,反演结果是真正的地震波波前传播的速度,因此反演结果更加直接和真实。本文利用射线追踪法求取层速度,首先利用下行波的初至时间求取观测井段以上地层的层速度,再利用上行波求取观测井段以下地层层速度。为逆时偏移提供更加准确的层速度模型。非零井源距VSP弹性波逆时偏移主要由三个部分组成：成像条件的计算,井中记录逆时传播的实现,成像条件的应用。本文从二维各向同性介质中的弹性波动方程出发,在交错网格空间中推导了弹性波场逆时延拓的高精度有限差分格式,给出了弹性波场逆时延拓的完美匹配层吸收边界条件,通过求解程函方程获取VSP地震资料逆时偏移的成像条件,在此基础上实现了非零井源距VSP多分量地震资料联合逆时深度偏移。更多还原

【Abstract】 Compared with surface seismic profile which is derived from the receiver on the surface, vertical seismic profile is derived from the receiver underground. The waves’ motive and dynamic characteristics are more conspicuous because it is by observing the wave field distribution in the vertical direction to study the geological section of the vertical changes. VSP not only has higher signal/noise ratio and resolution, but also can record up going and down going wave and can provide a more accurate processing and interpretation of time-depth conversion and velocity model for surface seismic processing and reliable identification of seismic reflection layer geologic position for calibration Compared with the surface seismic technology. VSP data to extract more pure seismic wavelet can be used on the surface seismic data deconvolution to improve resolution of surface seismic data. Offset VSP can also well away from the well of the ground around the structure and a higher vertical and horizontal imagination through the VSP P-wave and converted wave of research can effectively obtain the changes of lithology parameters. This article focus on the imagination of offset VSP processing.Seismic modeling is a very effective seismic data processing aids, elastic wave equation can be fully and accurately describe the dynamic characteristics of seismic waves and kinematics of offset VSP to do is wave equation modeling, is Mass media about elastic wave field characteristics and propagation of an important method, to design and develop a more rational approach and process. In the staggered grid of the discrete differential equations, elastic wave equation is derived time difference of second order accuracy, order accuracy finite difference scheme for differential space; with perfectly matched layer (PML) absorbing boundary condition to solve the truncated wave boundary layer reflection problem, the numerical accuracy of the synthetic records calculated.Three-component offset VSP recorded observation wave field is very complex. The various wave fields are often mixed together, to separate the work of a great deal of inconvenience. This article chooses a kind of two-step method for wave field separation by the polarization characteristics and apparent velocity characteristics of the wave field of three-component offset VSP data. the first scanning through the polarization filter based on angle, the original records in the complex wave field separation into simple wave field, and then a simple wave field as the velocity filter, separating the up going and under going wave field, in order to the separation of the various waves.Because the VSP data contains a wealth of seismic wave velocity, inversion of seismic wave in the real rate of spread, the result is more direct and true inversion, VSP seismic interval velocity inversion has a considerable advantage. In this paper, ray tracing method to find the interval velocity. The first arrival time of down going wave is used to strike the interval velocity of the layer in the above of the receivers; the up going wave is used to strike the interval velocity of the layer under receivers, for the reverse time migration interval velocity to provide a more accurate model.Offset VSP elastic wave reverse time migration mainly composed of three parts: computation of the imaging conditions, reverse time extrapolation of the recorded data, and application of the imaging condition at each time step during the extrapolation. This article derived a high order finite difference reverse time extrapolation scheme in the staggered grid for two dimensional isotropic media, and a perfectly matched layer(PML) absorbing boundary conditions applicable to reverse-time migration of elastic waves is also derived in the paper. The imaging condition is computed by solving the eikonal equations. On the basis of above techniques, a prestack reverse-time depth migration algorithm of multi-component offset VSP data is developed.更多还原