Unstable Density-Driven Flow in Fractured Porous Media: The Fractured Elder Problem

• Published in: Fluids (Basel) Vol. 4; no. 3; p. 168
• Main Authors: Shafabakhsh, Paiman, Fahs, Marwan, Ataie-Ashtiani, Behzad, Simmons, Craig T.
• Format: Journal Article
• Language: English
• Published: Basel MDPI AG 09-09-2019; MDPI
• Subjects: Boundary conditions; Convection; Convective flow; Density; Earth Sciences; Elder problem; Engineering Sciences; Environmental Engineering; Environmental Sciences; fingering; Finite element method; Flow distribution; Flow pattern; Fluids mechanics; fractured porous media; Fractures; Free convection; Heterogeneity; Hydrology; instability; Mechanics; Networks; Permeability; Porous media; Rayleigh number; Sciences of the Universe; Sherwood number; Solute transport; convection; fractured porous media; Sherwood number; Elder problem; fingering; instability
• ISSN: 2311-5521; 2311-5521
• DOI: 10.3390/fluids4030168

The Elder problem is one of the well-known examples of an unstable density-driven flow (DDF) and solute transport in porous media. The goal of this research is to investigate the influence of fracture networks on this benchmark problem due to the great importance of the fractured heterogeneity effect on unstable DDF. For this aim, the fractured Elder problem is solved using COMSOL Multiphysics, which is a finite element method simulator. Uniform and orthogonal fracture networks are embedded to analyze free convective flow and development of unstable salt plumes. The results indicate that the mesh sensitivity of the fractured Elder problem is greater than the homogeneous case. Furthermore, it has been shown that in the fractured cases, the onset of instability and free convection occur with lower critical Rayleigh number, which means that fracture networks have a destabilizing effect. Also, we examined the structural properties of fracture networks that control convective flow patterns, and the simulation results show that the strength of convection and instability at the beginning of the intrusion is proportional to the aperture size of the fractures. Moreover, the increase of the fracture’s density leads different modes of transient convective modes, until a specific fracture density after which the transient convective modes become similar to the homogenous case.