非均匀正交各向异性特征参数地震散射反演方法研究

摘要

在长波长假设条件下,水平层状地层中发育一组垂直排列的裂缝构成了等效正交各向异性介质.各向异性参数与裂缝弱度参数的估算有助于非均匀各向异性介质的各向异性特征描述,而弹性逆散射理论是非均匀介质参数反演的有效途径.基于地震散射理论,我们首先推导了非均匀正交介质中纵波散射系数方程,并通过引入正交各向异性特征参数,提出了一种新颖的正交各向异性方位弹性阻抗参数化方法.为了提高反演的稳定性与横向连续性,我们发展了贝叶斯框架下的正交各向异性方位弹性阻抗反演方法,同时考虑了柯西稀疏约束正则化和平滑模型约束正则化,最终使用非线性的迭代重加权最小二乘策略实现了各向异性特征参数的稳定估算.模型和实际资料处理表明,反演结果与测井解释数据相吻合,证明了该方法能够稳定可靠地从方位叠前地震资料中获取各向异性特征参数,减小参数估算的不确定性,为非均匀正交介质的各向异性预测提供了一种高可靠性的地震反演方法.%A single set of vertically aligned fractures embedded in a horizontal fine layer can be considered to be a long-wavelength effective orthorhombic anisotropic medium.The estimation of anisotropic parameters and fracture weaknesses is of great importance to characterize the anisotropy of heterogeneous anisotropic media.The elastic inverse scattering theory is one of the effective tools to realize the inversion for the elastic and anisotropic parameters of such media.Based on this theory,we first derive a linearized PP-wave reflection coefficient in terms of Thomsen anisotropic parameters and fracture weaknesses in heterogeneous orthorhombic media.A novel parameterization method of azimuthally anisotropic elastic impedance is then proposed using the variant formulations of anisotropic parameters.To improve the inversion stability and the lateral continuity,we develop an anisotropic elastic impedance inversion with angles of incidence and azimuth inversion method in the Bayesian framework using the regularization of the Cauchy-sparse constraint,smoothing model constraint and the nonlinear iteratively reweighted least squares (IRLS) strategy to estimate the anisotropic parameters and fracture weaknesses.Tests on synthetic and real data show that the results agree well with well log interpretation,and validate that this method can estimate the anisotropic parameters stably and reliably,providing a robust tool for inversion of heterogeneous orthorhombic media.