基于孔隙粘弹性介质的AVO正演模拟及衰减分析

AVO forward modeling and attenuation analysis based on porous viscoelastic media

岩石的孔隙度、含流体饱和度、地层品质因子等参数是影响地震波振幅随偏移距变化(AVO)的重要因素。从孔隙介质的基本理论出发,在孔隙介质反射率法弹性波正演模拟的基础上,引入粘弹性介质模型,推导了孔隙粘弹性介质的频率-慢度域反射系数和透射系数表达式,建立了孔隙粘弹性介质反射率法正演模拟方法;采用反射率法求取了孔隙介质中快、慢纵波的反射系数和透射系数,分析了孔隙粘弹性介质的AVO特性和孔隙度、流体类型、品质因子等因素对AVO响应的影响。研究表明:通过慢度/角度转换,采用反射率法得到的反射系数和Zoeppritz方程精确解得出的反射系数基本吻合;气藏模型中的孔隙度和含水饱和度对储层顶、底的AVO特征都有影响,相比之下孔隙度的影响更大;由于粘弹性引起的振幅衰减只与介质本身的粘滞性有关,与顶、底界面的波阻抗差异无关;孔隙介质的参数和粘弹性参数都对AVO响应特征产生影响。

The parameters including porosity,fluid saturation and quality factor(Q)are important impact factors of AVO.Starting from the basic theory of porous media,on the basis of forward modeling by using reflectivity method on porous media,by introducing viscoelastic media model,we deduced the formula of reflection coefficient and transmission coefficient in frequency-slowness domain for porous viscoelastic media,and established the forward modeling by using reflectivity method on porous viscoelastic media.Moreover,reflectivity method was used to acquire the reflection coefficient and transmission coefficient of fast P-wave and slow P-wave in porous media.Meanwhile,the impact of porosity,fluid type and Qof porous viscoelastic media on AVO responses was studied.The research reveals that reflection coefficient obtained by reflectivity method matches well with the exact solution computed by Zoeppritz equation.The porosity and water saturation of gas reservoir model affect the AVO characteristics of reservoir at the top and the bottom, the porosity has more influence on the trend of AVO in contrast. Seismic wave attenuates greatly in viscoelastic medium.The amplitude of attenuation is involved in the viscosity of media,and not involved in the difference of wave impedance between the top and bottom boundary.The porous medium parameters and viscoelastic parameters both impact the characteristics of AVO responses.