【作者】 杨路；

【导师】 贾晓峰；

【作者基本信息】 中国科学技术大学 ， 固体地球物理学， 2017， 硕士

【摘要】 在二维地震偏移成像中,染色算法被证实可以有效地提高弱照明区域的信噪比。染色算法应用于逆时偏移过程中,与目标成像区域相关的染色波场和常规的震源波场同步正向传播。分别将染色波场和震源波场与反向传播的检波点波场进行互相关运算,我们可以获得两个成像结果:仅包含目标结构的成像结果,以及传统的逆时偏移成像结果。该成像过程需要消耗巨大的计算机内存用以存储波场,尤其是在大尺度三维地质模型中。为了使染色算法适用于三维逆时偏移,在交错网格有限差分机制下,我们提出一种将染色算法应用于三维声波模拟的方法,该方法适应于有限差分算子的空间精度。同时在染色算法应用于弹性波,电磁波等波动方程有限差分模拟问题中,该方法同样适用。考虑到内存消耗问题,在检波点波场反向传播的过程,我们采取随机边界条件(RBC)。利用保存的最后一步的检波点波场,我们可以重建所有时刻的检波点波场。同时,在染色波场和震源波场正向同步传播的过程中,我们采取拟最佳匹配层(NPML)边界条件。复杂地质模型上的数值实验表明RBC-NPML联合策略不仅可以最大程度地减少内存消耗,同时可以保证高质量的成像结果。通过该策略,我们将染色算法应用于三维逆时偏移成像。数值实验表明染色算法可以给出目标结构高信噪比的成像结果。更多还原

【Abstract】 The staining algorithm has been proven to generate high signal-to-noise ratio(S/N)imaging results in poorly illuminated areas in two-dimensional cases.In the staining algorithm,the stained wavefield relevant to the target area and regular source wave-field forward propagate synchronously.Cross-correlating these two wavefields with the backward propagated receiver wavefield separately,we obtain two images:the lo-cal image of the target area and the conventional reverse time migration(RTM)im-age.This imaging process costs massive computer memory for wavefield storage,espe-cially in large scale three-dimensional cases.To make the staining algorithm applicable to three-dimensional RTM,we develop a method to implement the staining algorithm in three-dimensional acoustic modelling in a standard staggered grid finite difference(FD)scheme.The implementation is adaptive to the order of spatial accuracy of the FD operator.The method can be applied to elastic,electromagnetic,and other wave equations.Taking the memory requirement into account,we adopt a random boundary condition(RBC)to backward extrapolate the receiver wavefield and reconstruct it by reverse propagation using the final wavefield snapshot only.Meanwhile,we forward simulate the stained wavefield and source wavefield simultaneously using the nearly perfectly matched layer(NPML)boundary.Experiments on a complex geologic model indicate that the RBC-NPML collaborative strategy not only minimizes the memory consumption but also guarantees high quality imaging results.We apply the staining al-gorithm to three-dimensional RTM via the proposed strategy.Numerical results show that our staining algorithm can produce high S/N images in the target areas with other structures effectively muted.更多还原