含夹层孔隙介质分界面上反透射系数特征研究

Characteristics of reflection and transmission coefficients at the interface of porous media sandwiched with a porous medium saturated with a viscous fluid

研究地震波在含黏性流体孔隙介质中的传播特性,对于识别油气储层、刻画流体边界、判识油水界面等有重要作用.通常利用地震波在孔隙介质分界面上的反透射系数特征,来实现这些方面的研究.顶、底层孔隙介质之间存在含黏性流体孔隙介质夹层时,夹层内岩石骨架、孔隙因子、孔隙流体等参数会对反透射系数产生影响.本文推导出含夹层孔隙介质分界面上的反透射系数方程,针对方程建立不同孔隙度的含夹层孔隙介质模型;基于模型实现孔隙介质分界面上的反透射系数特征研究,分别分析不同夹层厚度、不同频率情况下,反透射系数随入射角的变化规律.研究表明,快慢纵波及横波的反透射系数都会受到孔隙夹层的影响,受影响程度主要取决于夹层厚度和地质背景等因素;慢纵波反射和透射系数数值极小,且后者随夹层厚度的增加而迅速衰减;频率通过反透射系数方程本身和地震波速度两个因素直接或间接的影响地震波反透射特征,其值的增加会引起快纵波和横波反透射系数不同程度的衰减.

Studying the characteristics of seismic wave propagation in porous media saturated with a viscous fluid plays an important role in identifying oil and gas reservoirs,characterizing fluid boundaries,and analyzing oil and water identification.Usually,the characteristics of reflection and transmission coefficients of seismic waves at the interface of porous media are used to realize the research and application of these aspects.However,when there is an interlayer porous medium saturated with a viscous fluid between upper and bottom porous media,the parameters of rock skeleton,pore factors and pore fluids in the interlayer will affect the reflection and transmission coefficients.In this paper,the equation of reflection and transmission coefficients at the interface of porous media sandwiched with an interlayer is derived,and a geological model of sandstone porous media with different porosities is established.Based on the model,the characteristics of reflection and transmission coefficients at the interface are analyzed.The variations of the coefficients with incident angles are studied under different interlayer thickness and different frequencies,respectively.The results show that the reflection and transmission coefficients of the fast P-,slow P-and SV-waves are affected by the porous interlayer,and the degree of influence mainly depends on the thickness of the interlayer and the geological background.The values of reflection and transmission coefficients of the slow P-wave are very small,and the latter attenuates rapidly with the increase of the interlayer thickness.The frequency affects the characteristics of reflection and transmission coefficients directly or indirectly through the coefficient equation itself and the velocities of seismic waves.And the increase of its value will cause the attenuation of the reflection and transmission coefficients of the fast P-and SV-waves in various degrees.