近地表地震地质复杂性的一种定量分析方法  

A quantitative analysis method for the seismic geological complexity of near surface

作　　者：陈高祥[1] 符力耘[1] 于更新[1,2] 管西竹[1,3] 葛双成[4] 

机构地区：[1]中国科学院油气资源研究重点实验室中国科学院地质与地球物理研究所,北京100029 [2]北京华文学院,北京102206 [3]中海油研究总院,北京100027 [4]浙江省水利河口研究院,浙江310020

出　　处：《地球物理学报》2017年第3期1062-1072,共11页Chinese Journal of Geophysics

基　　金：国家自然科学基金项目(41130418;41374146);863国家高技术研究发展项目(2013AA064202)资助

摘　　要：复杂近地表散射衰减所有的地面观测波场,形成半随机半相干的近地表强散射噪音背景,弥漫整个炮集,淹没深层反射信号,是导致地震资料极低信噪比的主要原因.如何研究和评价近地表散射强度一直是石油勘探未解决的问题,这与起伏地表的粗糙度、近地表速度横向变化和结构倾角分布密切相关.基于前期复杂近地表边界元法波动方程数值模拟研究,本文提出一种复杂近地表散射振幅矩阵方法来分析近地表散射强度.首先对复杂近地表结构进行边界元配置方法离散,根据边界积分方程生成矩阵方程.我们不求解该矩阵方程(涉及海量计算),只是利用矩阵分析技术来解析矩阵方程中的散射振幅系数矩阵,研究复杂近地表结构对不同频率波场的散射强度.该方法利用边界元对近地表结构几何特征的精确表征,研究起伏地表和非规则地质分界面对地震波传播的影响,由基本解及其在边界上的法向导数经过高斯数值积分计算得到的散射振幅系数矩阵,不仅描述了任意两点之间的相互影响,同时还刻画了边界形状特征的影响,为评价不同地质结构的散射强度提供了可能性.作为初步评价手段,我们采用矩阵元素总和与矩阵维数之比作为表征散射振幅系数矩阵散射特征的标量复杂系数,通过理论和实际模型测试,形成了一套行之有效、计算快速的近地表复杂性分析方法.Complexity of the near surface is a major factor causing low signal-to-noise ratio in seismic data; it scatters and attenuates all the wavefields observed on the surface, which causes semi-random and semi-coherent near surface scattering background noise on shot gathers that mask deep reflected signals. How to study and evaluate the near surface scattering intensity has long been an unsolved problem in petroleum exploration, which is closely related to the roughness of surface, the near surface lateral velocity variation, and the angle distribution of oblique structures. Based on previous researches on wave equation numerical simulation for complex near surface amplitu surface structure de matrix structure using boundary element method, this article puts forward a complex scattering method to analyze the scattering intensity near surface. First the complex near is discretized and collocated according to the boundary element method so as to form the matrix equation of the boundary integral equation. Instead of solving the matrix equations, which involves massive computation, we analyze the coefficient matrix of scattering amplitude by matrix analysis techniques in quest of the influence of complex near surface structure on different-frequency wavefields. This strategy uses the advantage of the boundary element method in accurately describing the geometrical characteristics of arbitrary boundaries to investigate how undulating surface and non-regular geological interface affect seismic wave propagation. The coefficient matrix of scattering amplitude is obtained by Gaussian numerical integration of the normal derivative of the fundamental solution on boundaries. This not only describes the interaction between two arbitrary points, but also includes the effect of morphological characters of different boundary elements, which provides the possibility for the evaluation of scattering intensities of different geological structures. As a preliminary evaluation method, we divide the summation of the matrix elements by its

关 键 词：近地表复杂性定量分析 散射振幅系数矩阵 边界元离散 标量复杂系数 

分 类 号：P631[天文地球—地质矿产勘探]