各向异性衰减薄层地震响应特征研究

薄储层的叠前地震响应特征研究,特别是针对具有速度各向异性的含流体薄层,对储层描述具有十分重要的意义.文中基于波动方程数值模拟方法,正演得到各向同性弹性、各向同性衰减、速度各向异性、各向异性衰减模型的地震波场,并对比分析了四种模型的纵波(PP)和转换横波(PS)地震反射特征.研究结果表明:在衰减介质背景下,引入各向异性,PP和PS波的反射波振幅较弹性介质均减弱,且衰减因素对薄层振幅的影响强于各向异性.同时,VTI各向异性衰减在单频PS振幅曲线上表现出强差异性,而HTI各向异性衰减则会影响PP和PS波单频振幅曲线的极值点幅值和位置,通过分析单频振幅曲线的极值点振幅和极值点位置对各向异性衰减薄层预测有指导作用,尤其对平时较难分辨的VTI各向异性衰减薄层,单频分析方法的优势更明显.

An analysis of seismic responses in thin anisotropic-viscoelastic reservoirs

Study on the prestack seismic responses of thin reservoirs, especially of the thin fluid-saturated layer with velocity anisotropy, is of great significance in reservoir interpretation. In this paper, the seismic wavefields in isotropic-elastic, isotropic-viscoelastic, velocity anisotropic and anisotropic-viscoelastic media are constructed by use of the numerical method, and a comparison is made to reveal seismic reflection characteristics of PP and PS waves. The results show that the reflection amplitude of PP and PS waves in the anisotropic-viscoelastic medium is weaker than that of the elastic medium when anisotropy is added to the viscoelastic medium, and the effect of attenuation on the thin-layer amplitude is stronger than that of anisotropy. At the same time, VTI attenuation shows strong difference in the single frequency PS amplitude curve, and the HTI attenuation affects the magnitude and position of the extreme points on both of PP and PS wave single frequency amplitude curves. The characteristic of amplitude and position of the extreme point on the single frequency amplitude curve gives a perspective to predict anisotropic-viscoelastic thin reservoirs, especially the viscoelastic VTI thin-layer reservoirs.