基于波动方程的叠前地震反演

随着地震勘探和开发的不断深入,面向地质目标的精细储层预测技术变得越来越重要.由于透射损失、层间多次波、波模式转换以及随机噪声等的影响,观测地震数据和待反演的地下介质属性之间呈现出很强的非线性.考虑到这些非线性,本文基于积分波动方程开展叠前地震反演,从观测地震数据中恢复出介质属性和整体波场,其中反演参数是波动方程中的压缩系数、剪切柔度和密度的对比度,相比于常规线性AVO反演的波阻抗弹性参数,它们对流体指示有更强的敏感性.在反演过程中,从平滑的低频背景场出发,交替迭代求解数据方程和目标方程.采用乘性正则化方法于共轭梯度框架下求解反演参数,采用优化的散射级数Neumann序列获得整体波场,这种方法不易陷入局部极值,能收敛到正确解.测井资料和典型山前带模型测试表明,利用上述反演方法能获得高分辨率的深度域地下介质属性,可直接进行储层预测和解释.

Prestack seismic inversion based on wave-equation

With the steady deeping of seismic exploration and development, geological target oriented fine reservoir prediction technology becomes more and more important. Because of the influences of transmission loss, multiple waves, mode-conversions and random noise, the relationship between observational seismic data and subsurface media property is essentially nonlinear. In view of this nonlinear relationship, a prestack seismic inversion based on integral wave equation was carried out in this work, which recovers the subsurface media property and total wavefield from the observation seismic data. During this process, the inversion parameters in the wave equation are contrasts of compressibility (1/bulk-modulus), shear compliance (1/shear modulus) and density. These parameters show stronger sensibility to oil and gas fluid indication than impedance properties that logically follow from the linearized reflectivity model. Starting from a smooth background, the data equation and domain equation were alternatively and iteratively solved, in which contrast parameters were inverted with multiplicative regularization based on the conjugate gradient method, total wavefield were updated with scattering series Neumann sequence. With this scheme, it seems less likely to be trapped in local minima and converges to the exact solution. Tests on well-log synthetic and the typically foothill belt model show high resolution of inversion results in the deep domain from the suggested inversion method in this paper, which could be used directly for reservoir prediction and interpretation.