含裂隙孔隙介质中纵波传播特征研究
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摘要
基于准静态孔隙弹性理论和White模型,给出了垂直于层面传播纵波的频散方程。在周期性层状孔隙介质中采用具有高孔隙度的柔性层表征裂隙从而构成裂隙孔隙介质,利用周期性层状孔隙介质的频散方程并综合线性滑动裂隙模型,推导出裂隙孔隙介质中垂直于裂隙传播纵波的等效介质模型。裂隙孔隙介质中介观尺度上的流体流动作用所引起的纵波速度频散与衰减值远高于Biot流作用,特征频率或衰减峰值通常可位于地震频段。介质中纵波速度频散及逆品质因子均会随裂隙弱度(密度)的增大而增大,背景孔隙介质的渗透率与粘度以及裂隙的间隔与弱度共同决定特征频率的大小。
The periodic layered porous media is used to present the fractured porous media with mesoscopic inhomogeneities.Based on quasi-static poroelastic theory and White model,the effective medium model of P-wave propagating normal to the layer is given.The thinner layer in the periodic layered porous media can be substituted by a very thin and highly compliant layer to model fractures in a porous background.Compared with linear-slip fracture model,a dispersion equation for a P-wave propagating normal to fracture is given.The magnitude of velocity dispersion and energy attenuation of Pwave caused by wave induced pore fluid flow between pores and fractures are apparently larger than that of Biot fluid,and their peak value often lies in the seismic frequency band.The magnitude of velocity dispersion and attenuation of P-wave will increase monotonically with the increase of fracture weakness(fracture density).The characteristic frequency of the attenuation and velocity dispersion of P-wave depends both on the permeability and fluid viscosity of background porous media and on the fracture weakness and spacing.
引文
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