【作者】 刘冰；

【导师】 张凯；

【作者基本信息】 中国石油大学(华东) ， 地质资源与地质工程， 2019， 硕士

【摘要】 全波形反演(FWI)可以构建高分辨率的速度模型,它是根据叠前地震波场的运动学、动力学信息来重建地下速度结构,能够揭示复杂地质背景的结构和岩性细节信息。根据实际需要,可以在时间、频率、拉普拉斯域实现全波形反演。从计算方法的角度来看,全波形反演的实现方法主要包括梯度引导法和牛顿法(高斯牛顿法)。但是在实际勘探数据处理方面仍然存在许多问题:由于地下波场的复杂性,会导致反演问题的非线性性增强,在寻优的过程中易陷入局部极值;常规的全波形反演无法解决数据低频缺失的问题,当地震数据缺乏低频信息时,如何恢复地下介质的长波长分量是问题的重中之重。为了解决这个问题,在本文中,首先从正演开始,推导了相关公式,给出了加PML边界和无PML边界波场炮记录的对比图,然后通过对FWI分辨率进行分析,给出了FWI方法对地下介质尺度的反演极限,及其与观测系统的关系,再根据分辨率分析的结论,提出利用经验模态分解(Empirical Mode Decomposition,简称EMD)的方法对观测数据进行分解,使观测数据分解为有限个本征模函数(Intrinsic Mode Function,简称IMF),所分解出来的各IMF分量包含了原信号的不同时间尺度的局部特征信号,从而得到对应地下大尺度构造的波形,然后用于波形反演。经验模态分解方法是以傅立叶变换为基础的线性和稳态频谱分析,该方法是依据数据自身的时间尺度特征来进行信号分解,无须预先设定任何基函数。因而在处理非平稳及非线性数据上,具有非常明显的优势,适合于分析非线性、非平稳信号序列,具有很高的信噪比。所以,经验模态分解法在地震记录分析方面相比于其他方法具有很大的优势。论文最后,利用盐丘模型测试表明了上述方法的有效性。更多还原

【Abstract】 Full waveform inversion(FWI) can construct a high-resolution velocity model,which reconstructs the subsurface velocity structure based on the kinematics and dynamics information of the prestack seismic wavefield,and can reveal the structural and lithological details of the complex geological background.According to actual needs,full waveform inversion can be realized in time,frequency and Laplacian domain.From the point of view of calculation methods,the implementation methods of full waveform inversion mainly include gradient guidance method and Newton method(Gaussian Newton method).However,there are still many problems in the actual exploration data processing: due to the complexity of the underground wave field,the nonlinearity of the inversion problem will be enhanced,and it will fall into the local extremum in the process of optimization;the conventional full waveform inversion cannot To solve the problem of low frequency data loss,when the seismic data lacks low frequency information,how to recover the long wavelength component of the underground medium is the most important issue.In order to solve this problem,in this paper,we first derive the relevant formula from the beginning of the forward performance,and give a comparison chart of the PML boundary and the PML-free boundary wave field cannon record.Then,by analyzing the FWI resolution,we give The FWI method’s inversion limit of the subsurface medium scale and its relationship with the observation system,according to the conclusion of the resolution analysis,it is proposed to use the Empirical Mode Decomposition(EMD)method to decompose the observation data.The observed data is decomposed into a finite number of Intrinsic Mode Functions(IMFs).The IMF components are separated into local characteristic signals of different time scales of the original signal,so that the waveform corresponding to the underground large-scale structure is obtained,and then Used for waveform inversion.The empirical mode decomposition method is a linear and steady-state spectrum analysis based on Fourier transform.The method performs signal decomposition based on the time scale characteristics of the data itself,without pre-setting any basis functions.Therefore,it has obvious advantages in dealing with non-stationary and nonlinear data.It is suitable for analyzing nonlinear and non-stationary signal sequences and has a high signal-to-noise ratio.Therefore,the empirical mode decomposition method has great advantages in seismic record analysis compared to other methods.At the end of the paper,the salt hill model test shows the effectiveness of the above method.更多还原