多组垂直裂缝诱导各向异性的HTI近似及其特征分析

在裂缝诱导各向异性理论研究中通常使用等效HTI介质来近似多组裂缝所引起的综合效应.由于构造运动的复杂性,多组裂缝普遍存在于地壳与油气储层中.为了研究多组裂缝的地震属性特征,分析常用的等效HTI模型对于多组裂缝近似精度及附加裂缝对介质属性特征的影响,本文利用线性滑移模型进行了多组垂直裂缝的单斜各向异性等效介质理论计算,并利用空间搜索方法求取与其最为接近的HTI介质各向异性弹性参数.重点研究了在两种各向异性介质中纵波速度、快慢横波速度和极化特征及其差异,量化分析附加裂缝对于地震属性如速度、极化方向和走时等的影响,研究对附加裂缝敏感的地震属性.此研究结果和方法为进一步研究多组裂缝的反演及识别方法提供基础,同时对于将高阶对称性各向异性介质中已存在的计算方法应用于低阶对称性时的适用程度、精度分析及相关方法研究具有重要作用.

Equivalent HTI approximation and characteristics of anisotropy induced by multiple sets of vertical fractures

Equivalent HTI medium is commonly used to approximate combined effects of multiple groups of fractures in theoretical study of fracture-induced anisotropy. Due to complex tectonic movement, multiple sets of fractures are prevailed in crust and oil and gas reservoirs. In order to study the seismic attributes and analyze the approximation accuracy of the equivalent HTI model for multiple sets of fractures, this study uses a linear slip model of the equivalent medium theory to calculate the monoclinic anisotropy for multiple sets of fractures and obtain the closest equivalent anisotropic elastic parameters of the HTI medium by scanning the shortest spatial distance. The differences in P wave velocity, fast and low shear wave velocity and polarization characteristics of the two types of anisotropic media are discussed in detail and quantitative analysis of the effects of additional cracks on seismic attributes such as velocity, polarization direction and travel time is conducted to find the most sensitive attribute to the existence of additional fractures. The results provide a basis for development of inversion methods of multiple sets of fractures and play an important role in the applicability, precision analysis and research on application of relevant existing methods as the high-order anisotropic symmetry is used to approximated the low-order symmetry.