横向各向同性介质中的AVO

介质各向异性是影响振幅随炮检距变化的重要因素之一。本文将Ａｋｉ和Ｒｒｃｈａｒｄａ的方法进行推广，推导出两个弹性横向各向同性介质密接条件下平面波反射和透射系数，并给出弱弹性ＴＩ假设下的近似式。近似式的物理意义明确，而且精度明显于前人的结果。

AVO in transverse isotropic medium

The anisotropy of medium is one of the significant factors which disturb ampli-tude variation with offset (AVO)- The reflection and transmission coefficient ex-pressions of plane waves in two elastic transversely-isotropic (TI) media underwelded contact condition have been deduced by generalizing the expressions of Akiand Richards,and the approximate expressions of the coefficients in weak elastic TImedium are given in this article- The expressions have definite geophysical meaningsand bring higher accuracy than others. The P-P approximate expression indicatesthat Thomsonsen's anisotropic parameter 3 difference between upper and lower lay-ers plays an important role in AVO when incident angle ranges from small degreesto middle degrees, but the difference of P-wave anisotropic parameter fy can havestrong influence on AVO when incident angle is above 2O degrees. As far as P-Pwave AVO fitting is concerned,TI doesn' t affect zero-offset reflection coefficients,but causes direct influence on the "gradient"- For three types of isotropic gas sand-stones (high impedance,near zero impedance contrast,and low impedance),we anal-yse the influence of TI overlying shale on P-P AVO. The research says that TI over-lying shale may make a water-bearinR sandstone exhibit better AVO Dhen0menOn.