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

Abstract

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.

Convective-reactive transport of dissolved CO2 in fractured-geological formations

“…The kinetic dissolution reactions are included as source terms in the transport equations. To include fractures via the discrete fracture approach (1D), we used the interface "Fracture flow" as in (Koohbor et al, 2019;Mozafari et al, 2018;Shafabakhsh et al, 2019). The system of flow and transport equations are solved simultaneously using the fully coupled approach in COMSOL.…”

“…The effects of fractures on non-reactive DDC processes have been extensively investigated in the literature but not in the context of CO2 sequestration (Hirthe and Graf, 2015;Jafari Raad and Hassanzadeh, 2018;Shafabakhsh et al, 2019;Simmons et al, 2008).…”

Hydrogeological constraints for the genesis of the extreme lithium enrichment in the Salar de Atacama (NE Chile): A thermohaline flow modelling approach

“…The leaking of concentrated brines would prevent the salt flats to reach extremely high concentrations (Sanford and Wood, 1991). Furthermore, fault planes are frequently associated with preferential flow paths due to their higher permeability combined with the development of convective cells (Barcelona et al, 2019;Hirthe and Graf, 2015;Koltzer et al, 2017;Li et al, 2016;Magri et al, 2016Magri et al, , 2015Magri et al, , 2010Shafabakhsh et al, 2019;Simms and Garven, 2004;Zechner et al, 2019). However, although previous work has highlighted the necessity of addressing thermohaline circulation in salt flats (e.g., Godfrey and Álvarez-Amado, 2020;Hardie, 1991Hardie, , 1990Magaritz et al, 1990;Munk et al, 2016;Risacher et al, 2003;Rosen, 1994), only synthetic models focused on the saline interface of the shallowest aquifers have been performed to date (Duffy and Al-Hassan, 1988;Fan et al, 1997;Hamann et al, 2015;Holzbecher, 2005;Marazuela et al, 2018;Nield et al, 2008;Simmons et al, 1999;Tejeda et al, 2003;Vásquez et al, 2013).…”

Gill's stability problem may be unstable with horizontal heterogeneity in permeability

“…Salibindla et al (2018) conducted an experimental investigation of the dissolution convection in a porous medium with multiscale heterogeneity and some important implications for the future estimation of subsurface carbon sequestration were presented. Shafabakhsh et al (2019) considered the influence of a fractured heterogeneity effect on unstable density-driven flow. It was shown that the onset of instability and free convection occur with a lower critical Rayleigh number, indicating the fractured networks have a destabilizing effect.…”

“…Shafabakhsh et al. (2019) considered the influence of a fractured heterogeneity effect on unstable density-driven flow. It was shown that the onset of instability and free convection occur with a lower critical Rayleigh number, indicating the fractured networks have a destabilizing effect.…”