Seismic estimation of the fluid factor and shear modulus plays an important role in reservoir fluid identification and characterization. Various amplitude variation with offset inversion methods have been used to estimate these two parameters, which are generally based on approximate formulations of the Zoeppritz equations. However, the accuracy of these methods is limited because the forward modeling ability of approximate equations is incorrect under the conditions of strong impedance contrast and large incidence angles. Therefore, to improve the estimation accuracy, we have used the Zoeppritz equations to directly invert for the fluid factor and shear modulus. Based on the poroelasticity theory, we derive the Zoeppritz equations in a new form containing the fluid factor, shear modulus, density, and dry-rock velocity ratio squared. The objective function is then constructed using these equations in a Bayesian framework with the addition of a differentiable Laplace distribution blockiness constraint term to the prior model to enhance the fluid boundaries. Finally, the nonlinear objective function is solved by combining the Taylor expansion and the iterative reweighted least-squares algorithm. Numerical experiments indicate that the inversion accuracy of our method may heavily depend on the parameter of the dry-rock velocity ratio square that is assumed to be static. However, tests on synthetic and field data show that our method can estimate the fluid factor and shear modulus with satisfactory accuracy in the case of choosing a reasonable static value of this parameter. In addition, we determine that the accuracy of this method is higher than that of the linearized formulation.

中文翻译：

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流体因子和剪切模量的稳健 AVO 反演

流体因子和剪切模量的地震估计在储层流体识别和表征中起着重要作用。已经使用偏移反演方法的各种幅度变化来估计这两个参数，这些参数通常基于 Zoeppritz 方程的近似公式。然而，这些方法的准确性是有限的，因为在强阻抗对比和大入射角条件下，近似方程的正演能力是不正确的。因此，为了提高估计精度，我们使用 Zoeppritz 方程直接反演流体因子和剪切模量。基于多孔弹性理论，我们推导出了包含流体因子、剪切模量、密度和干岩速度比平方的新形式的 Zoeppritz 方程。然后在贝叶斯框架中使用这些方程构建目标函数，并向先验模型添加可微拉普拉斯分布块状约束项以增强流体边界。最后，结合泰勒展开和迭代重加权最小二乘算法求解非线性目标函数。数值实验表明，我们方法的反演精度可能在很大程度上取决于假设为静态的干岩速度比平方参数。然而，对合成和现场数据的测试表明，在选择合理的静态参数值的情况下，我们的方法可以以令人满意的精度估计流体因子和剪切模量。此外，