基于各向异性AVO的裂缝弹性参数叠前反演方法

基于各向异性理论,将具有水平对称轴的高角度裂缝介质等效为HTI介质。首先,通过分析HTI介质反射界面的纵波反射系数公式,研究裂缝介质振幅随偏移距和方位角的变化特征,探索了方位各向异性介质弹性参数和各向异性参数的叠前反演方法。其次,为更好地估测介质的弹性参数:纵波阻抗IP、横波阻抗IS以及各向异性梯度Γ,对反射系数近似式进行了简化,同时对简化公式的精度进行了对比分析。最后,选取2D逆掩断层模型,利用褶积公式制作不同方位的合成地震道集,并对合成地震道集添加随机噪声(信噪比为2∶1),将其应用于方位AVO叠前反演算法试算中。结果表明,当信噪比为2时,方位AVO叠前反演所得纵波阻抗、横波阻抗及各向异性梯度的估测值与模型真实值基本吻合,而且估测值能够较准确地反映原始模型的地层特征,验证了方位AVO叠前反演算法的准确适用性。

Method of Fracture Elastic Parameter Inversion Based on Anisotropic AVO

Based on anisotropic theory,the authors considered fractured reservoir with the horizontal axis of symmetry and high-angle equivalent of HTI media.First of all,by analysis of P wave reflection coefficient formula,it studied the characterization about amplitude versus offset and azimuth,and explored the pre-stack estimation method for anisotropic elastic and anisotropic parameters.Secondly,in order to estimate the elastic parameters of the medium: longitudinal wave impedance,IP,shear wave impedance,IS,and anisotropic gradient Γ better,the study made a simplification of the reflection coefficient,and analyzed the accuracy of the simplified formula.Finally,it selected 2D overthrust model to test azimuth AVO pre-stack inversion method.The authors used the convolution formula to produce synthetic seismic gathers in different directions,added random noise to synthetic seismic gather(signal to noise ratio is 2∶1),and applied it to the azimuth AVO pre-stack inversion algorithm test.The results showed that the value which estimated by using the azimuth AVO pre-stack inversion method,longitudinal wave impedance,shear wave impedance and anisotropic gradient,was consistent with the true value of the overthrust model basically,and the estimation value could more accurately describe the stratigraphic features of original model,and it verified the applicability accuracy of the azimuth AVO pre-stack inversion algorithm.