【作者】 巴晶；

【导师】 杨慧珠；

【作者基本信息】 清华大学 ， 力学， 2008， 博士

【摘要】 孔隙介质中的地震波传播研究一直是地球物理与石油勘探领域的一个热点。该问题源自不同尺度的孔隙、裂缝、溶洞与岩石骨架之间的耦合作用所产生的复杂地震特征。目前的研究主要集中于探索孔隙介质的地震衰减机制,存在的问题包括复杂多孔介质的物理描述以及数值实现。针对该问题,本文分析了松弛骨架机制、松弛耗散机制的地震波响应特征,基于傅立叶变换数值模拟了含中观流双孔介质的地震波场。实际储层中的岩石是一种非完全弹性的材料,特别是当流体渗入后,岩体往往表现出较强的粘弹性。本文基于Biot理论,考虑了多孔介质中的固体骨架的松弛特征。引入纵波品质因子、横波品质因子与耗散品质因子三参数描述孔隙介质中的松弛机制,采用虚谱法在地震频段进行波场模拟,数值模拟得到的结果,与Carcione1999年的计算结果以及其2006年得到的结论不符,本文的模拟结果证实,松弛骨架机制不仅适用于高频段,也可用于解释地震频段下的弹性波衰减现象,以描述固体微细颗粒的中观松弛特征。为进一步从反演角度验证松弛骨架对低频地震的重要影响,本文对地震降噪与浅层粘弹性反演问题进行了研究。针对地震反演预处理的地震降噪问题,本文结合小波分析设计了一种过零点滤波器,对多分量地震资料进行了面波剔除研究。采用小生境遗传算法对虚拟模型以及中国东部某地区的低频资料进行了多参数反演,反演结果显示浅土层具有可从地震资料直接观测的品质因子,这一点证明了松弛骨架模型的合理性与有效性。为调查孔隙流体流动与地震衰减之间的内在联系,本文推导了含中观流双孔介质中Biot绝对位移格式的波动方程,基于伪谱法给出一种离散傅立叶变换求解中观流的数值算法,模拟了含Biot耗散与中观流多孔介质中的地震波场。对无流体流动、含中观流体流动与含两种流体流动的三个模型进行了对比模拟,结果显示:中观流体流动会将快纵波的能量转移给慢纵波,慢纵波的能量迅速衰减仍然需要归因于Biot耗散机制。更多还原

【Abstract】 The research of seismic waves propagation in porous medium is one of the hotspot in the field of Geophysics and petroleum Exploration research. Problems of these kinds of porosity come from the different-scale coupling effects between pores, fractures, caves and solid skeletons. Current work is focused on seismic attenuation mechanism in porous rocks, and the remaining problems include physical description and numerical simulation about complex porous rocks. This thesis analyzes the skeletion-relaxed mechanism and the diffusion-relaxed mechanism in porovisco- elastic medium, and simulates the wavefields through a pesudo-spectral method in the double-porosity rocks with mesoscopic fluid flow(MFF).Actual reservoir rocks are anelastic materials, especially when they are saturated with some kind of fluid, which will make the viscoelastic characteristics more significant. In the poroviscoelasticity theory, the relaxation effect is considered based on the Biot’s theory. Three parameters of P wave quality factor, S wave quality factor and diffusion quality factor are introduced to describe the relaxation effect in porous medium. A pseudo-spectral method is used in forward modelling, and simulation results disagree with Carcione’s points(1999, 2006). Low-frequency poroviscoelastic modelling shows that the skeleton-relaxed mechanism can also be used to describe the seismic band attenuation for elastic waves. It has the physical meaning of mesoscopic relaxation effect between the small grain particles.Furthermore, the thesis also studies the problems in seismic denoising and parameters inversion to assess a relaxed solid skeleton’s influence on low frequency band attenuation. In the denoising and preprocessing for seismic inversion, a zero-crossing filter is developed based on wavelet analysis to remove surface waves from the multi-component seismic data. Niche Genetic Algorithms Inversions on the numercial models and actual seismic records from east China show that shallow layer soil has a viscoelastic nature in solid particles, and its quality factor can be directly estimated from observation. The inversion also proves the skeleton-relaxed mechanism’s reasonability and validity.To investigate the intrinsic relationships between seismic attenuation and pore fluid flow, the thesis derives the Biot’s absolute displacement form of the wave equations in double-porosity rocks, and provides a discrete algorithm to numerically solve the fluid increments caused by MFF. Wavefield is simulated in double-porosity rocks with MFF and Biot diffusion, and the three models are compared in the numerical experiment, which include model with none fluid flow, model with MFF, and model with MFF and Biot flow. Results show MFF will transfer the fast waves’energy to slow waves, and the high attenuation of the second kind of slow P wave can be explained with the Biot diffusive mode.更多还原