流体流动对孔隙裂缝介质中地震波传播影响研究

Study of Fluid-Flow Effects on Seismic Propagation in Fractured Porous Media

摘要: 前人已经对裂缝岩石介质中的地震波传播开展了大量研究。这些研究大多在背景介质为弹性固体的假设前提下考虑裂缝各种参数对地震速度的影响。然而实际地下裂缝岩石的背景是岩石颗粒和流体并存的孔隙介质。最近的实验研究表明不仅岩石结构会影响地震波速度，而且由动态应力所引起的孔隙裂缝中的流体流动也会对地震速度产生显著的影响。本文在含定向排列裂缝的孔隙介质中，研究流体流动对地震波传播的影响。主要通过Hudson理论和各向异性Gassmann理论求得干燥、低频流体饱和以及高频流体饱三种情况下的地震波速度，将它们进行对比发现，流体流动会对裂缝各向异性介质中的地震波产生影响：准纵波(qP)和准SV(qSV)波发生明显的速度频散现象，且它们频散的大小和波传播的方向有关；流体流动对准SH(qSH)波影响不大。

Abstract: Many researches on seismic propagation in fractured rocks have been done, but almost all centered on fracture parameters’ effects on the assumption that the backgrounds are simple elastic solids. In reality the backgrounds are complex porous media where solid rock grain and fluid coexist. Recent experimental researches imply that not only rock structure, but also fluid-flow in porous and fracture space that caused by dynamic stress can affect seismic wave in fractured media. In this paper, the effect of fluid-flow in porous media with aligned fractures is studied. Hudson’s fracture theory and Gassmann equation in anisotropic media are adopted to compute seismic velocities. In dry condition, low-frequency fluid-saturation condition and high-frequency fluid-saturation condition, Seismic velocities are computed. Comparing these results we find that fluid-flow can change seismic velocities in anisotropic fractured porous medium, which make qP wave and qSV wave dispersion, and the dispersion magnitude is related propagation direction. But it nearly has no effect on qSH wave.