傅里叶有限差分法保幅叠前深度偏移方法

A method of Fourier finite-difference preserved-amplitude prestack depth migration

地震数据中饱含有丰富的走时信息和振幅信息.为解决传统偏移方法中几何扩散和入射角变化引起的振幅误差问题,本文提出了一种实用的波动方程保幅地震偏移方法.该方法从全声波方程出发进行单程波保幅分解,得到直观、高效率的直接面对地震波传播波场的压力分量进行延拓的保幅偏移单程波方程,进而推导出一个含有6项的傅里叶有限差分法保幅偏移的算子方程;修改边界条件和成像条件,使修改后的边界条件和成像方程中考虑振幅补偿,从而从三方面补偿几何扩散损失和入射角变化对振幅的影响.脉冲响应测试、单炮记录的数值试验以及SEG/EAGE盐丘模型的叠前偏移结果表明,该方法不但可以使散射能量聚焦、归位,提高成像精度;而且可以输出正确反映地下反射系数的振幅信息,为后续的地震属性分析(如AVO/AVA)提供更真实的地震信息.

Seismic data contain rich travel-time and amplitude information. In order to solve the problem of amplitude errors caused by geometric spreading and incidence angle variations, we propose a practical wave equation preserved-amplitude migration method. In this method, we derive the high efficiency direct-viewing one-way wave equation for preserved- amplitude migration from full acoustic wave equation using one-way wave＇s preserved-amplitude decomposition, which is extrapolated while facing the pressure component of the seismic wavefield. Then we derive a 6-item operator equation based on the method of Fourier finite-difference preserved- amplitude migration, and modify boundary conditions and imaging conditions to take amplitude compensation into account in modified boundary conditions and imaging equations. So we compensate for amplitudes affected by geometric spreading loss and incidence angle variations from three aspects above. Theoretical model testing and real data processing indicate that this method not only can make scattering energy be focused and migrated to the correct position to improve imaging accuracy, but also can output the amplitude information which reflects the correct subsurface reflection coefficients. So this method can provide more real seismic information for following attribute analysis, such as AVO/AVA.