Physical mechanism of seismic attenuation in a two-phase medium  

双相介质中地震波衰减的物理机制(英文)

作　　者：李子顺[1] 

机构地区：[1]大庆油田勘探开发研究院,大庆163712

出　　处：《Applied Geophysics》2008年第1期9-17,共9页应用地球物理（英文版）

摘　　要：High-frequency seismic attenuation is conventionally attributed to anelastic absorption. In this paper, I present three studies on high-frequency seismic attenuation and propose that the physical mechanism results from the interference of elastic microscopic multiple scattering waves. First, I propose a new theory on wave propagation in a two-phase medium which is based on the concept that the basic unit for wave propagation is a nano- mass point. As a result of the elasticity variations of pore fluid and rock framework, micro multiple scattering waves would emerge at the wavelength of the seismic waves passing through the two-phase medium and their interference and overlap would generate high- frequency seismic attenuation. Second, I present a study of the frequency response of seismic transmitted waves by modeling thin-layers with thicknesses no larger than pore diameters. Results indicate that high-frequency seismic waves attenuate slightly in a near-surface water zone but decay significantly in a near-surface gas zone. Third, I analyze the seismic attenuation characteristics in near-surface water and gas zones using dual-well shots in the Songliao Basin, and demonstrate that the high-frequency seismic waves attenuate slightly in water zones but in gas zones the 160-1600 Hz propagating waves decay significantly. The seismic attenuation characteristics from field observations coincide with the modeling results. Conclusions drawn from these studies theoretically support seismic attenuation recovery.通常认为地震波高频衰减的物理机制主要是滞弹性的吸收,本文通过如下三方面的研究认为地震波高频衰减的物理机制主要是弹性的微观多次散射波的相互干涉。(1)本文提出了双相介质波动新理论,认为地震波传播的基本单元是纳米级的质点,由于双相介质孔隙流体和骨架岩石弹性性质的不同,地震波在双相介质中传播时,无论波长大小在孔隙流体或骨架岩石中将会产生微观多次散射波,微观多次散射波叠加相互干涉,可使地震波高频视衰减。(2)用厚度如同孔隙直径的薄层模型分析了地震透射波的频率特性,结果表明类似于近地表水层中传播的地震波高频成分衰减不大,类似于近地表气层中传播的地震波的高频成分衰减幅度巨大。(3)用松辽盆地双井微地震测井分析了近地表水层和气层中地震波衰减特性,表明水层中传播的地震波高频成分衰减很小,气层中传播的地震波160-1600Hz的高频成分大幅度衰减。野外观测的水层和气层中的地震波高频衰减特征与厚度如同孔隙直径的薄层模型中微观多次散射波叠加相互干涉的视衰减特征一致。本文研究成果为恢复地震高频衰减奠定了理论基础。

关 键 词：two-phase medium seismic attenuation NANOMETER wave propagation theory multiple scattering waves. 

分 类 号：P631.4[天文地球—地质矿产勘探]