亚波长尺度裂缝地震散射分辨分析

裂缝储层地震特征的准确识别已成为当前地震勘探的难点之一, 特别是深层礁滩或碳酸盐岩储层, 其大部分裂缝都在亚波长尺度, 按照传统地震反射四分之一波长几何分辨准则是不能完全分辨的.传统研究裂缝地震响应的方法主要基于各向异性等效介质理论, 但由于亚波长尺度裂缝微小且其地震反射弱并存在噪声干扰等问题, 故该传统方法逼近精度有限.然而, 这类部分可分辨裂缝可在地震散射范畴来分析和预测, 本文基于散射聚焦分辨分析理论, 提出了表征裂缝系统空间分布和形态特征的波数域散射成像矩阵方法, 据此计算了含裂缝与不含裂缝的波数域成像矩阵之间的振幅差异性和结构差异性, 从散射能量及其各向异性的角度分析了亚波长尺度裂缝的地震可识别性.均匀和复杂背景介质下的算例表明, 振幅差异性随裂缝厚度和密度的变化规律显著, 结构差异性随裂缝角度变化规律更加明显.同时讨论了随机噪声和排列长度等因素对裂缝系统地震散射可识别性的影响.排列长度和噪声对于裂缝厚度响应影响较小, 主要影响高角度裂缝的识别, 同时要求排列长度大于三倍目标深度才可应用该方法进行裂缝参数识别.

Seismic scattering resolution analysis of subwavelength scale fractures

Accurately identifying the seismic characteristics of fractured reservoirs has become one of the main challenges in current seismic exploration, especially for deep reefs or carbonate reservoirs, which are mostly sub-wavelength scale and cannot be fully resolved using the traditional quarter-wavelength geometric resolution criteria of seismic reflection. Traditional methods for studying the seismic responses of fractures mainly rely on anisotropic equivalent medium theory. This paper proposes a wavenumber-domain scattering imaging matrix method based on the scattering focusing resolution analysis theory to characterize the spatial distribution and morphological characteristics of fracture systems. Specifically, this method calculates the differences in amplitude and structure between wavenumber-domain imaging matrices with and without fractures. This paper analyzes the seismic recognizability of sub-wavelength scale fractures from the perspectives of scattering energy and anisotropy. Numerical cases under uniform and complex background media demonstrate that amplitude differences are better suited for identifying the thickness and density of fractures, while structure differences are better suited for identifying the angle of fractures. The paper also discusses how complex media, random noise and array length affect the seismic scattering recognizability of fracture systems. The array length has minimal effect on the response of fracture thickness, but it significantly affects the recognition of high-angle fractures. Therefore, it is necessary that the array length be at least three times the target depth.