【作者】 佟威；

【导师】 刘学伟；

【作者基本信息】 中国地质大学（北京） ， 地球探测与信息技术， 2009， 硕士

【摘要】 地震波在传播过程中的能量衰减特征,表现为:一方面为球面扩散,另一方面是由于实际的地层为非弹性介质而引起的吸收衰减,它由于岩石存在的内摩擦性及粘滞性,使得地震波在传播过程中能量得到衰减,且高频能量衰减强,低频能量衰减弱。过去的研究结果已证实:球面扩散是降低反射信号能量的主要因素;吸收是使反射信号频带宽度变窄的主要因素,其中表层吸收尤为严重。地震波衰减的一个重要物理参量是介质的吸收系数或品质因子Q值,它描述了介质非完全弹性特征,它是地层的内部本质特性.对表层品质因子做出可靠的估计,不仅可以通过反Q滤波来提高分辨率,而且它对岩性和流体性质如饱和度、孔隙度、渗透率是很重要的信息,可与速度信息互相补充用于岩性解释。人们对第四系以下固结良好地层的吸收规律研究较多,并给出了理论表达式和Q值与速度之间的经验公式,对表层未固结成岩的低速带的吸收规律研究甚少。从地震数据中提取衰减信息是一个重要的问题,对表层吸收衰减Q值的反演更是非常有意义、有挑战性的工作。一般的第四系以下的Q值都是依靠专门的采集技术或VSP资料获得。本文在现有资料(野外的VSP数据)的基础上,研究了2种方法(谱比法和时间域统计法)估算Q值,建立了Q值估算流程,通过统计获得近地表的Q参数。提出了由吸收系数求取Q值的方法—时间域统计法,利用微测井地面接收的共检波点记录,通过近地表结构的变化分析,对实际振幅值采取必要的处理手段,并结合施工地区的经验公式,由第四系以下固结良好地层的吸收规律,来了解表层未固结成岩的低速带的衰减情况。在这种方法中,为了寻求更加合理的Q值分布规律,采用了分段分析和分层拟合的方式,并对Q值做适当的标定,结果证明可以获得接近真实地层的Q值。该方法可以在求取固结岩层的Q值的同时,使表层Q可以像深层Q值一样成像,并得到表层Q值与表层速度的关系表达式。对已有的谱比法,进行了改进,通过迭代分析和迭代处理,并进行人工干预,尽量减弱激发和接收不一致性的影响,逐步提高近地表Q值的估算精度。在应用于实际资料时,谱比方法由于信噪比的原因,有时求得的值并不可靠。最后对影响Q值估算精度的主要因素进行了分析。更多还原

【Abstract】 In spreading process, the energy decay of the seismic wave depends on the attenuation caused by the stratums’viscoelastic nature besides geometrical spreading. Because of inner friction and viscidity in the rocks, we can get strong high-frequency and weak low-frequency attenuation. Past research shows that geometrical attenuation is the main factor of geometrical spreading energy, and absorption is the main factor of narrowed signal bandwith, especially around the near surface.The coefficient of absorption (α) or quality factor (Q) is the important parameter of the seismic attenuation, which depicts viscoelastic nature of the medium and represents stratum’s internal nature character. The faithful values of the quality factor not only improve seismic resolution through inverse Q deconvolution, but also can be used as the information of the lithologic interpretation with the velocity because it is sensitive to parameters such as saturation, porosity and permeability. The researches of the absorption regular of the consolidated layers have much more than that of the unconsolidated layers.Inversion of the surface quality factor is a very significant work. Q can be obtained by means of technical know-how collection or VSP datum. In the base of the available field VSP datum, the work develops two methods to estimate Q, builds Q estimation flow chart, and at last acquires Q values in the near surface. It proposes the statistical method in time domain in which the coefficient of absorption first is calculated. It utilizes the VSP common detector gathers received on the surface, process the actual amplitude through analysis of the near surface structure alternation, get the quality factor values of the low velocity layer in the surface by means of building region’s empirical formula. In this method, sectional analysis and differential fit and calibrating procedure are used, and the result shows that Q can be concordant with real layers. This method can get the relational expression of the unconsolidated layer’s Q and velocity just like that of the consolidated layer. The spectral ratio method is improved by means of iterative process and artificial interpose in order to abate the different response of same instrument. In practice, the result may be misleading and not reliable for the low S/N ratio. At last, main factors of accuracy affected for Q estimation are analyzed.更多还原