Simulation of fracture propagation induced acoustic emission in porous media

Abstract

Acoustic/microseismic Emissions (AE) in naturally fractured geological formations are the result of local material instability/failure (both shear and tensile) and the rapid dynamic release of strain energy stored in the rock matrix. This rapid release of energy may result in inertia effects and stimulation of high-frequency components in the dynamic response of the system; a process that appears in the form of an induced AE. In this article, enhanced finite element models in the framework of the Partition-of-Unity (PU) finite element are employed to simulate dynamic fracture propagation and induced AE in porous media. The versatility of the Phantom Node Method (PNM) in modelling strong discontinuities independently of the original mesh is combined with the wave propagation simulation capabilities of a Generalized Finite Element Model (GFEM) to investigate the induced AE characteristics. The cohesive fracture methodology is implemented in the context of the Mixed GFEM-enriched PNM (PNM-GFEM-M) method to model the stress degradation/localization behaviour in the fracture process zone. Effects of different system properties such as permeability, material damping, and material ductility on dynamic crack propagation and the induced AE are investigated through several numerical examples. It is demonstrated that the employed enriched finite element model (PNM-GFEM-M) results in fewer spurious oscillations in induced AE signals compared to the regular finite element models (unenriched PNM).