摘要
实际地球介质并非完全弹性介质,地层吸收特性致使地震波在地层中传播存在能量衰减及速度频散现象。地层吸收与岩石的岩性、渗透性、孔隙度、饱和度以及含流体类型有密切联系。地震波吸收衰减研究已经成为地震学研究的热门课题之一。开展衰减介质中地震波响应特征分析及地层吸收衰减属性提取具有重要理论和实际意义。
衰减介质中波场传播算子的建立是单程波动方程正演模拟的基础。通过衰减介质模型对比分析,本文基于Futterman模型振幅衰减和速度频散原理将地层吸收衰减定量表征参数—地层品质因子Q与弹性介质纵波波场延拓算子相结合,推导了衰减介质单程波方程复波数波场传播公式,建立了衰减介质分步傅里叶波场传播算子和傅里叶有限差分波场传播算子。
本文基于衰减介质单程波波场传播理论,采用反射波正向传播理论,实现了衰减介质中单程波法非零偏移距和零偏移地震波正演模拟和偏移。在不影响计算精度的前提下大大提高了计算的效率,克服了基于检波点波场下延原理进行炮记录计算效率低的问题。通过数值模拟进行单程波法与双程波法地震波场特征分析,探索衰减介质中地震波传播规律。在此基础上建立了基于衰减介质的不同吸收分布模型地震响应特征模式。
地层吸收衰减属性与储层特征相关,地层吸收衰减参数的提取至关重要。本文基于S变换时频分析方法,推导了不同偏移距下视地层Q值以及地层吸收系数与偏移距之间的变化关系。以衰减介质中地震反射波频谱能量高低频成分非对称理论为基础,计算地层相对吸收系数,并推导了相对吸收系数与偏移距之间关系。在本论文中通过横向开窗采用多道拟合的方法,得到零偏移距地层相对吸收系数。同时通过理论模型和实际资料验证了方法的可行性。
As the earth is not perfectly elastic actually, seismic waves traveling in the earth experience amplitude attenuation and velocity dispersion because of earth attenuation. Absorption is related to the properties of rocks, such as lithology, permeability, porosity, saturation and the type of fluid content. As one of the leading-edge topics in seismology study, seismic attenuation study is of theoretical and practical significance for the response characteristics of seismic wave attenuation properties and absorption and attenuation properties extract from seismic data.
Wave field propagator in attenuation medium is the foundation of one-way wave equation modeling. In this paper, based on Futterman equation, we combine the quality factor Q, a parameter for quantitative characterization of absorption and attenuation, with the P wave propagation operator in elastic medium. We derive the wave propagation equation with complex wave number in attenuation medium using one-way wave equation, and then we establish SSF and FFD operator in attenuation medium.
On the basis of the theory of wave propagation by one-way wave equation in attenuation medium, using physical principles of the reflected wave propagation, this paper achieve nonzero-offset seismic pre-stack forward modeling and migration in attenuation medium by one-way wave equation, which greatly improves the computation efficiency. With numerical simulation, we compare the characteristics of one-way wave equation and two-way wave equation and explore seismic wave propagation in the attenuation medium. On this basis, this paper built seismic wave propagation characteristics in different attenuation media.
Attenuation estimated from seismic data is important for it relates to lithology, permeability, porosity, saturation and the type of fluid content. In this paper, based on S transform time-frequency analysis, we derived appear quality factor in different offset and the relationship of absorption coefficient with the offset. As seismic energy of high frequency and low frequency is asymmetric in attenuation medium, we compute the relative effective absorption coefficient,and derive association of relative absorption coefficient with offset. Through the use of multi-trace or lateral window we obtain zero-offset stratum relative absorption coefficient. The application in synthetic data and practical data demonstrate the feasibility of the method.
引文
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