品质因子反演与粘声波动方程偏移

发布时间：2018-01-12 06:41

本文关键词：品质因子反演与粘声波动方程偏移　出处：《西南石油大学》2017年硕士论文　论文类型：学位论文

【摘要】：地下介质并非理想的弹性介质,地震波在其中传播时存在吸收衰减现象。由于声波波动方程不反映介质的吸收衰减特性,故偏移结果不能准确地反映介质的岩性和物性变化。考虑到介质的粘弹性时,偏移处理应采用粘声波动方程,即在延拓的同时对衰减能量进行补偿。介质的吸收衰减特性可采用品质因子刻画,精准反演出品质因子是粘声波动方程偏移的前提。地震波的吸收衰减与其频率成分以及传播时间有关,频率越高、传播时间越长吸收衰减就越重。当衰减后的能量降低到数值计算精度范围以下时,直接对其进行粘声波动方程偏移就会引起不稳定现象,表现为补偿后能量异常,因此,稳定性条件是粘声波动方程偏移必须考虑的问题。针对品质因子反演中的难题,首先对粘弹性介质的吸收机理、波尔茨蔓原理及典型粘弹性介质模型进行了研究;随后阐述了时间域、频率域以及时频域具有代表性的品质因子反演方法及原理,并对数值模拟结果采用不同方法进行品质因子反演,分析不同方法的反演精度及抗噪性,选取最优方法。结果表明理想情况下,频谱比法反演精度最高,基于S变换的频谱比法次之,振幅衰减法最差;在含噪情况下,基于S变换的频谱比法反演精度最高抗噪性最好,频谱比法次之,振幅衰减法最差。针对粘声波动方程偏移过程中存在的不稳定现象,在前人研究基础上,结合逐层约束思想推导出新的稳定性条件公式。在波场延拓过程中,改变循环变量的层级结构,将深度循环置于最外层,从而可以求取不同深度对应的稳定性条件。首先使用相移法偏移对稳定性条件进行测试,再使用裂步傅里叶法对复杂模型正演结果进行偏移处理,最后利用本文方法对实际资料进行处理,本文方法处理结果较传统处理方法在能量补偿,拓宽频带以及提高分辨率方面有一定改善。
[Abstract]:The underground medium is not an ideal elastic medium in which the seismic wave propagates the phenomenon of absorption and attenuation. The wave equation of acoustic wave does not reflect the absorption and attenuation characteristics of the medium. Therefore, migration results can not accurately reflect the lithology and physical properties of the medium. Considering the viscoelasticity of the medium, the viscoacoustic wave equation should be used in migration processing. That is to say, the attenuation energy is compensated while the continuation is carried out. The absorption and attenuation characteristics of the medium can be characterized by the quality factor. Accurate inversion of the quality factor is the premise of viscoacoustic wave equation migration. The absorption and attenuation of seismic wave is related to its frequency composition and propagation time, and the higher the frequency is. The longer the propagation time, the heavier the absorption and attenuation. When the energy after attenuation is reduced to the precision range of numerical calculation, the phenomenon of instability will be caused by the visco-acoustic wave equation migration directly. Because of the energy anomaly after compensation, the stability condition is the problem that must be considered in the migration of viscoacoustic wave equation. In view of the difficulty in quality factor inversion, the absorption mechanism of viscoelastic medium is first discussed. The Poltzmann principle and the typical viscoelastic medium model are studied. Then the time domain and frequency domain are represented by the time frequency domain quality factor inversion method and principle, and the numerical simulation results using different methods to carry out the quality factor inversion. The inversion accuracy and noise resistance of different methods are analyzed and the optimal method is selected. The results show that the spectral ratio method has the highest inversion accuracy in ideal case, followed by the spectrum ratio method based on S transform, and the amplitude attenuation method is the worst. In the case of noise, the inversion accuracy of spectrum ratio method based on S-transform is the best, the spectrum ratio method is the second, and the amplitude attenuation method is the worst. On the basis of previous studies, a new stability condition formula is derived by combining the thought of layer by layer constraint. In the process of wave field continuation, the hierarchical structure of cyclic variables is changed and the depth cycle is placed at the outermost layer. Therefore, the stability conditions corresponding to different depths can be obtained. Firstly, phase shift migration is used to test the stability conditions, and then the crack step Fourier method is used to process the forward modeling results of the complex model. Finally, the method is used to process the actual data. The results of this method are better than that of the traditional method in energy compensation, broadening the frequency band and improving the resolution.
【学位授予单位】：西南石油大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：P631.4;P618.13

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