介观尺度孔隙流体流动作用对纵波传播特征的影响研究——以周期性层状孔隙介质为例  

A study of the influence of mesoscopic pore fluid flow on the propagation properties of compressional wave—a case of periodic layered porous media

作　　者：邓继新[1,2] 王尚旭[3] 杜伟[2] 

机构地区：[1]油气藏地质及开发工程国家重点实验室(成都理工大学),成都610059 [2]成都理工大学地球物理学院地球物理与勘察技术系,成都610059 [3]中国石油大学CNPC物探重点实验室,北京102249

出　　处：《地球物理学报》2012年第8期2716-2727,共12页Chinese Journal of Geophysics

基　　金：国家重点基础研究发展计划(973)项目(2007CB209600);国家自然科学基金项目(40804025)资助

摘　　要：介观尺度孔隙流体流动是地震频段岩石表现出较强速度频散与衰减的主要作用.利用周期性层状孔隙介质模型,基于准静态孔弹性理论给出了模型中孔隙压力、孔隙流体相对运动速度以及固体骨架位移等物理量的数学解析表达式,同时利用Biot理论将其扩展至全频段条件下,克服了传统White模型中介质分界面处流体压力不连续的假设.在此基础上对准静态与全频段下模型介质中孔隙压力、孔隙流体相对运动速度变化形式及其对弹性波传播特征的影响进行了讨论,为更有效理解介观尺度下流体流动耗散和频散机制提供物理依据.研究结果表明,低频条件下快纵波孔压在介质层内近于定值,慢纵波通过流体扩散改变总孔隙压力,随频率的增加慢波所形成的流体扩散作用逐渐减弱致使介质中总孔压逐渐接近于快纵波孔压,在较高频率下孔压与应力的二次耦合作用使总孔压超过快纵波孔压.介质中孔隙流体相对运动速度与慢纵波形成的流体相对运动速度变化形式一致;随频率的增加孔隙流体逐渐从排水的弛豫状态过渡到非弛豫状态,其纵波速度-含水饱和度变化形式也从符合孔隙流体均匀分布模式过渡到斑块分布模式,同时介质在不同含水饱和度下的衰减峰值与慢纵波所形成的孔隙流体相对流动速度具有明显的相关性.Wave induced pore fluid flow at mesoscopic scale can cause obvious velocity dispersion and attenuation of compressional wave at seismic frequency.In this paper,the periodic layered porous media is used to represent the porous media with mesoscopic inhomogeneities,and the analytical expressions of pore pressure,relative flow velocity of pore fluid and frame displacement are given for this model based on quasi-static poroelastic theory,and the above results are also extended to full frequency range using Biot theory,which are more reasonable from physical view due to that the present model considers the continuity of fluid pressure at the interface between constituent layers.Based on those works,the variation of pore pressure,relative flow velocity of pore fluid and their influences on the properties of elastic wave propagation are studied,which can provide more physical understanding for the damping mechanism related to the wave induced pore fluid flow at mesoscopic scale.Pore pressure induced by fast compressional wave is almost constant in each layer of the model at low frequency range,and slow compressional wave will change the net pore pressure through fluid diffusion.But at relatively high frequency,the total pore pressure can exceed the pore pressure induced by fast compressional wave,and the additional pore pressure is a result of the secondary coupling of pore pressure with stress.We can also find that almost all of the contribution of the relative flow velocity arises from the slow compressional wave.The variation pattern of the velocity of compressional wave as a function of water saturation can change from homogeneous saturation to patchy saturation with the increasing frequency.There is a positive correlation between the value of quality factor and the relative fluid velocity.

关 键 词：介观尺度 孔隙流体流动 速度频散 衰减 弹性波 

分 类 号：P631[天文地球—地质矿产勘探]