基于EMT采用FEM研究含裂纹介质中弹性波传播机制

了解和掌握弹性波在含有裂纹介质中的传播规律是开发利用页岩气等非常规油气资源中的关键科学问题.本文基于数值模拟的优点,采用商用有限元软件Nastran模拟弹性波在含裂纹介质中的激发及传播方式,分析了弹性波在该介质中裂纹微结构(密度和纵横比)对弹性波传播动力学特性的依赖程度.结果表明:有限元方法(FEM)可以用于该问题的研究;Hudson等效介质理论(EMT)不适用泊松比近0.5的材料;裂纹密度、纵横比的增大会减小纵波(P波)波速值,以及衰减位移时域响应的首波振幅,且裂纹密度对于该材料的各向异性的影响要远大于纵横比的作用.

Wave propagation in cracked elastic media based on EMT using FEM

Understanding mechanism of wave propagation in elastic media with cracks is the key scientific issue in exploration and extraction of shale and other unconventional oil and gas resources. Based on the advantages of the numerical simulation, the excitation and propagation of elastic wave in the cracked media were simulated by Nastran, a commercial solver for finite element analysis. Then the dependence of dynamic characteristics of propagation in that kind of media was further analyzed based on the microstructure (crack density, aspect ratio). Some conclusions were obtained as follows. Finite element method (FEM) would be effectively used to study the issue. Hudson's effective medium theory (EMT) could not be applied into materials with Poisson's ratio of nearly 0.5. Increasing crack density and aspect ratio would reduce the primary wave (P wave) velocity, with decaying the displacement amplitude of the P wave in time-domain. Crack density of the medium exposes greater effect on the anisotropy than the aspect ratio.