低速破碎带弹性波场特征数值模拟研究

Numerical simulation of elastic wave field characteristics in low velocity fractured zone

页岩气的开发需要对地层进行水平井压裂,在压裂过程中会产生地下破碎带。破碎带会对地震波的传播产生影响,较为明显的现象是,由于低速薄层的存在,地震波"陷入"在薄层内形成"导波"。文中基于弹性波方程的交错、变网格高阶有限差分正演模拟,研究了低速破碎带地层弹性波波场特征;针对破碎带呈现的各向异性和随机特征,建立了均匀异性介质模型和各向异性随机介质模型,进行了弹性波场数值模拟。结果表明:低速破碎带对地震波能量有"禁锢"作用;各向异性介质模型模拟的波场清晰,适用于页岩气储层压裂分析;破裂导致的随机扰动分布致使波场存在较强散射。

Horizontal well fracturing is necessary when developing shale gas. In the process of fracturing, the fractured zones appear in the formation, which influences seismic wave propagation. An obvious phenomenon is the appearance of guided wave caused by low velocity fractured zone. Based on the crisscross of elastic wave equation and the forward modeling of variable grid high-order finite difference, this paper studies the elastic wave field characteristics of low velocity fractured zone. Aimed at the anisotropy and random characteristics of fractured zone, homogeneous anisotropic medium model and anisotropic random medium model are established and the numerical simulation of elastic wave field is conducted. The results show that low velocity fractured zone has locked up role on seismic wave energy; the wave field modeled by anisotropic medium model is clear, which is available for the analysis of shale gas reservoir fracturing, the random pertm-bation distribution caused by fracture is introduced, which results in a strong scattering in wave field.