基于孔隙介质理论的地震反射特征分析

在地层中传播的地震波特征受到岩性、孔隙结构、含流体性质等因素的复杂改造作用,孔隙介质理论可以更有效地模拟和分析储层的地震反射特征。将实际介质等效为固体基质和孔隙流体组成孔隙介质,按岩石物理建模方法,建立含流体储层弹性参数与物性参数之间的定量关系,根据孔隙介质的Zoeppritz方程详细讨论了几个典型储层物性参数变化对反射波AVO特征的影响,并将其与按球面波理论正演模拟计算的归一化振幅的AVO特征进行对比分析,发现孔隙介质理论的反射系数与归一化振幅更为接近,尤其是在入射角较小时。泥质含量和孔隙度可导致储层AVO类型发生变化,而孔隙流体性质变化引起AVO截距发生变化,但AVO类型基本不变。孔隙流体性质对AVO特征的影响相较于泥质含量和孔隙度要小得多。本文的方法为利用地震数据进行流体识别提供了更为可靠的理论依据。

Analyses of seismic reflection characteristic based on porous medium theory

The characteristics of seismic waves propagating in reservoirs are complicatedly altered by factors such as lithology, pore structure and fluid properties, Based on the porous medium theory, the seismic reflection characteristics of the reservoir can be simulated and analyzed more effectively. In this paper, the actual medium is equivalent to the porous media composed of solid matrix and pore fluid. Based on rock physical modeling, the quantitative relationship between elastic parameters and physical parameters of fluid saturated reservoir is established. According to the Zoeppritz equation of porous media, the influence of physical parameters on the AVO characteristics of reflected waves are analyzed and compared with that of normalized amplitudes of forward-modeled CMP gathers based on the spherical wave theory. The results show that the reflection coefficients of porous media theory and normalized amplitudes are much closer, especially when the incidence angle is small. Changes of shale content or porosity lead to changes in the AVO type. Changes of fluid properties cause changes only in the AVO intercept to change, while the AVO type remains unchanged. The effect of pore fluid properties on AVO characteristics is much smaller than that of shale content or porosity. The method in this paper provides more reliable theoretical basis for fluid identification using seismic data.