基于双孔模型的含流体各向异性介质地震波场数值模拟

裂缝的存在是诱导地下介质产生各向异性的主要原因,而裂缝中的流体则能够对地震波产生十分明显的能量衰减。本文基于双重孔隙介质理论,对含流体各向异性介质的地震响应特征进行了数值模拟,发现双孔介质的各向异性与介质的渗透率、裂缝密度、有效压力和频率均有重要联系。基于衰减各向异性理论,推导了含流体各向异性介质二维三分量应力-应变关系,结合旋转交错网格有限差分法,通过数值模拟给出了双孔介质中地震波的传播规律,结果表明裂缝密度的增大能够显著地增强介质的各向异性,使得q P波和快慢q S波垂直或平行于裂缝面的波前面均更接近椭圆,且流体的存在能够对q P和q S波相速度造成较为显著的衰减。

Seismic Wavefield Simulation of Fluid-saturated Anisotropic Media Based on Dual-porosity Model

Anisotropy of subsurface media is induced by fractures, and the filled fluid can make remarkable attenuation to seismic energy. We present this work by simulating the seismic response characteristics of fluid-saturated anisotropic media based on dual-porosity media theory. And we discover that the anisotropy of dual-porosity media is connected with the permeability, fracture porosity, effective pressure and frequency. With the attenuative anisotropy theory, we derivate the two-dimensional and three-component stress-strain relationship of fluid-saturated anisotropic media. Utilizing finite difference method of rotated staggered grid, we simulate the seismic wave propagation of dual-porosity media. The result demonstrates that the increasing of fracture porosity leads to remarkable increasing of anisotropy, making the wave-form of qP and qS wave closer to ellipse and the presence of fluid also make great influence on the attenuation of qP and qS wave phase velocity.