HTI构造煤方位AVO正演

Azimuthal AVO in HTI tectonic coal

以HTI介质为例,在已知入射波射线参数条件下,精确求解了透射波速度和角度,在此基础上,推导出方位AVO响应的精确表达式,并通过分析两种模型的AVO散射系数曲线,得到以下认识:1对于上层为均匀各向同性介质,下层为HTI介质的模型1,纵波反射系数最大值出现在90°方位,在靠近90°方位上波动小,在靠近0°和180°方位上波动大;快横波反射系数经过裂隙面和对称轴面发生极性反转,且峰值未出现在裂隙面和对称轴面,慢横波反射系数变化规律与之相反。2对于上、下层均为HTI介质,且对称轴夹角取不同值的模型2,方位角相差180°的纵波反射系数曲线重合;当上、下层介质对称轴夹角为0°和90°时,纵波反射曲线关于裂隙面和对称轴面重合;快横波反射曲线在对称轴面发生连续性反转,在裂隙面发生间断性反转,慢横波反射曲线的变化规律恰恰相反。3在裂隙面和对称轴面上,快、慢横波只出现一种。通过对比快、慢横波反射系数经过裂隙面和对称轴面极性反转的特点,可以准确地确定裂隙走向。

When the incident ray parameter is known,we can obtain the exact transmitted velocity and angle in HTI media.Then we deduce the exact AVO formula in azimuth based on this theory.Weobtain the following observation with analysis of AVO scattering curves of two models:1the maximum reflectivity of compression wave occurs at the azimuth of 90°on Model 1with isotropy homogeneous media over HTI media.The reflectivity changes little near 90°,but it changes a lot at 0°and 180°.At the same time the reflectivity of the fast shear wave has polarity reversal when it propagates across the symmetry axis plane and the fracture plane,but the reflectivity peak does not occur in these two planes.For the slow shear wave,it is opposite.2 As for model 2 with HTI over HTI whose symmetry axis planes have an arbitrary angle,whatever the angle of both symmetry axis planes is,the reflectivity of compression wave is the same if its incident angle difference in azimuth is 180°.When the angle of both symmetry axis planes is 0°and 90°,the reflectivity of compression wave is the same about the symmetry axis plane and the fracture plane.The reflectivity of fast shear wave has continuous polarity reversal across the symmetry axis plane,but discontinuous polarity reversal across the fracture plane.For slow shear wave,it is opposite.3 On the symmetry axis plane and the fracture plane,either fast shear or slow shear can occur.Based on the characteristics of fast and slow shear waves,we can precisely pinpoint the fracture strike.