【摘要】 介质的各向异性、孔隙率、流体饱和度及有效压力等是影响地震波振幅随炮检距变化 (AVO)的重要因素。本文在现有的地震波反射系数表达式基础上 ,通过合理的假设 ,推导出弱横向各向同性 (TI)介质中的反射系数近似表达式 ,在不降低精度的同时 ,表达式的形式大大简化 (振幅是炮检距或入射角的显函数 ) ,物理意义明确。并且研究了双相介质 (水—气、油—气 )孔隙率、流体饱和度和上覆岩层压力变化对反射波 AVO的影响。由于岩石孔隙流体饱和度对介质密度、纵波和横波速度及反射波振幅影响较大 ,本文尝试把饱和度变化对反射系数的影响表示成关于速度和密度值的显函数 (饱和度修正项 ) ,从而使长期以来被人们定性分析的饱和度对速度、密度及反射系数的影响定量化 ,对于不同压力、不同孔隙流体情形 ,得到的饱和度修正项均适用。更多还原

【Abstract】 The anisotropy,porosity,fluid saturation and effective pressure are the significant factors which effect on amplitude variation with offset (AVO) of seismic wave in the medium. Based on the well known expressions of reflectivity of plane wave and after some reasonable simplification,the approximate expressions of reflectivity in weak transversely isotropic medium are deduced in this paper. With the same accuracy as the well known expressions,our expressions are more simple (explicit function of amplitude vs offset or incident angle) and have definite physical meaning. The paper also studied the effects of porosity,fluid saturation in diphasic medium(water gas and oil gas) and change of overburden pressure on reflection wave AVO. Considering that fluid saturation has strong effects on density of medium,P wave and S wave velocity and reflection amplitude,we attempt to express the variation of reflectivity with different saturation by an explicit function of velocity and density(the updated expression of saturation),which quantitatively expresses the effect of saturation on velocity,density and reflectivity that people qualitatively analyzed right up to now. The updated expression of saturation can be suitable for different effective pressure and fluid type.更多还原