地震映像正演模拟分析及应用

发布时间：2018-04-25 17:18

本文选题：地震映像 + 正演模拟　；参考：《湖南科技大学》2015年硕士论文

【摘要】：地震映像法是在最佳偏移距反射波地震勘探的基础上发展起来的,具有数据采集高效、快捷,采集方式灵活和数据处理相对简单等优势,能有效的对空洞、溶洞、起伏基岩面、管线和大型混凝土构件的质量进行探测,作为浅层地震勘探的一种新方法已得到较为广泛的使用。地震映像资料中包含有时域和频域资料,目前在资料处理中主要利用时域数据,对频域资料利用甚少。利用时、频域对地震映像资料进行综合分析处理能有效提高解译的准确性。因此,对地震映像进行正演模拟,分析和总结不同模型条件下的地震映像记录的时频特征具有重要的理论和实际意义。本文在有限差分理论的基础上,采用交错网格法对二维弹性波动方程进行数值求解,获取差分格式,通过分析,选取二维一阶弹性波动方程交错网格有限差分作为震源处理方法,以变系数吸收边界为人工边界,建立了各向同性半空间模型、水平层状介质模型和含有低速异常体模型。在数学模型的基础上,编写相应地震映像正演模拟程序,进行数值模拟,获得了不同模型的地震映像波形记录和不同时间点的波场快照,并选取相关记录道进行S变换,得到S变换时-频分布图。从时域及频域角度分别对正演模拟所获得的成果进行分析、总结,得到以下几点认识:①在各向均匀介质中,地震波由激励点呈圆弧形向四周传播,能量逐步衰减,波形记录中以直达波为主;②介质呈水平层状结构时,波场快照显示,波传播层界面时会产生反射、折射和透射现象,波型发生转换,各种波在界面附近叠加,使波场复杂化,波形记录中存在着折射波、反射波和面波三种强能量,而在时-频分布图中表现为两个能量团,折射波和反射波因波至时间相差不大,在S变换过程中无法分离,叠加形成一个能量团,另一能量团由面波形成,随时间增长频率逐步衰减;③地震波传播在过程遇到低速体时,在低速异常体的角点处将会产生绕射现象,对角点附近的波场产生干扰,地震波在低速异常体顶部界面上无法产生折射波,但在底部界面能产生折射波,使接收到折射波的波至时间较两侧大,同时面波在低速异常体位置会出现振幅偏小甚至缺失现象,在时-频分布图上显示,面波主频较均匀介质和层状介质明显偏低,且地震波传播至低速体后频率迅速下降,能量快速衰减。将上述规律应用到实测地震映像资料的解释中,取得了较好的应用效果,验证了地震映像正演模拟结果的正确性,同时表明,通过正演模拟获得的不同模型条件下的时频特征对实测数据的解释具有一定的指导意义。
[Abstract]:The seismic mapping method is developed on the basis of the best offset reflection wave seismic exploration. It has the advantages of high efficiency, fast data acquisition, flexible acquisition method and relatively simple data processing. It can effectively deal with cavities, caverns and undulating bedrock surfaces. As a new method of shallow seismic exploration, the quality of pipeline and large concrete members has been widely used. There are time-domain and frequency-domain data in seismic image data. At present, time-domain data are mainly used in data processing, but frequency-domain data are seldom used. Comprehensive analysis and processing of seismic image data in time and frequency domain can effectively improve the accuracy of interpretation. Therefore, it is of great theoretical and practical significance to carry out forward modeling of seismic images and analyze and summarize the time-frequency characteristics of seismic image records under different model conditions. In this paper, based on the finite difference theory, the staggered grid method is used to solve the two-dimensional elastic wave equation numerically, and the difference scheme is obtained. Two dimensional first order elastic wave equation staggered grid finite difference method is selected as the focal processing method. The isotropic half-space model, horizontal layered medium model and the model with low velocity anomaly are established with the absorbing boundary of variable coefficient as artificial boundary. Based on the mathematical model, the corresponding forward simulation program of seismic image is compiled to simulate the seismic image waveform of different models and the snapshot of wave field at different time points. The time frequency distribution of S transform is obtained. The results of forward modeling are analyzed from time domain and frequency domain respectively, and the following conclusions are obtained: in every direction of homogeneous medium, the seismic wave propagates from excitation point to circumference, and the energy gradually attenuates. The wave field snapshot shows that reflection, refraction and transmission will occur at the interface of the wave propagation layer when the direct wave is the main medium with horizontal layered structure in the waveform recording, the wave pattern will be converted, and all kinds of waves will be superimposed near the interface, which will complicate the wave field. There are three kinds of strong energy in the waveform record: refraction wave, reflected wave and surface wave, but in the time-frequency distribution diagram there are two energy groups. The difference between refraction wave and reflected wave arrival time is not different, so it can not be separated in S transform process. Superimposed to form an energy mass, the other energy mass is formed by a surface wave. The propagation of seismic waves gradually attenuates with the increasing frequency of time. When the slow velocity body is encountered in the process, diffraction will occur at the corner of the low velocity abnormal body. The wave field near the diagonal point interferes, the seismic wave can not produce refraction wave at the top interface of the low velocity anomaly body, but it can produce the refraction wave at the bottom interface, so that the arrival time of the received refraction wave is longer than that of both sides. At the same time, the amplitude of the surface wave will be smaller or even absent in the position of the low velocity anomaly body. In the time-frequency distribution diagram, the main frequency of the surface wave is obviously lower than that of the homogeneous medium and the layered medium, and the frequency of the seismic wave decreases rapidly after the seismic wave propagates to the low velocity body. The energy decays rapidly. The application of the above rule to the interpretation of the measured seismic image data shows that the validity of the forward modeling results of the seismic image is verified, and it is also shown that, The time-frequency characteristics of different models obtained by forward modeling have a certain guiding significance to the interpretation of measured data.
【学位授予单位】：湖南科技大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P631.4

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