Reactive Flow and Homogenization in Anisotropic Media

Abstract

The evolution of heterogeneous and anisotropic media in the uniform dissolution regime (low Damköhler number) is studied here using a numerical network model. The uniform dissolution extensively homogenizes the medium and therefore the flow field. The homogenization is further enhanced when the surface reaction is transport controlled-when slow diffusion of dissolved ions away from the mineral surface leads to the reduction of the global dissolution rate. Under those conditions, diffusive transport is more effective in narrow channels, which selectively enlarge, leading to an initial steep rise of the permeability. However, as dissolution proceeds, the void space widens and the overall dissolution rate drops, and permeability enhancement slows down. Finally, we review the relevance of these results to various processes in geological systems ranging from diagenesis and karst evolution, to carbon geosequestration. These findings provide fundamental insights into reactive transport processes in fractured and porous media and evolution of permeability, tortuosity, anisotropy, and bulk reaction rates in geological systems. Plain Language Summary When corrosive fluids flow in an aquifer, they dissolve the rocks and change the void-space structure (e.g., acidic water invading limestone). In many geological processes and applications, the flow velocity is high compared to the chemical dissolution rate, and the corrosive fluid penetrates large distances before it loses its reactivity, resulting in relatively uniform dissolution everywhere. Here, using analog numerical model, we study how the void-space structure of porous rocks and aquifers change during uniform dissolution. In particular, we study how different initial structures and reaction conditions change the flow field and transport properties. Finally, we review the relevance of these results to various geological systems. The study improves our understanding of rock and aquifer evolution, with implications to groundwater management and other subsurface flow-related processes, such as CO 2 geosequestration.

Pore‐Scale Visualization and Quantification of Dissolution in Microfluidic Rough Channels

“…The variable L included in Equation suggests the important role of system size along the flow direction in the pattern transition. The result indicates that the uniform dissolution regime is scale‐dependent: the concentration field will fully develop downstream and leads to wedge dissolution if the system length, L , is large enough, whereas otherwise the uniform dissolution is observed (Li et al., 2008; Roded et al., 2020). Theoretical analysis and numerical simulation in three‐dimensional fractures have also demonstrated that fracture length plays an important role in the transition between wormhole and uniform dissolution patterns (Li et al., 2008; Starchenko & Ladd, 2018; Wang et al., 2022).…”

“…To isolate the effect of mineral heterogeneity that will obscure the effect of reaction and transport on morphological evolution, some simulations with single‐mineral have been performed recently as a precursor to understanding how the coupled effect of reaction and transport at the pore scale determines the evolution of the flow channels (Li et al., 2021; Noiriel & Soulaine, 2021; Roded et al., 2020; You & Lee, 2021). These studies show that when mass transport near the surface is slower than surface reaction, dissolution in the channels is transport‐controlled and the original rough channels are smoothed and flattened (Noiriel & Soulaine, 2021; Roded et al., 2020; You & Lee, 2021). When transport near the surface is faster than surface reaction, reaction‐controlled dissolution will preserve the original channel geometry (Roded et al., 2020).…”

“…These studies show that when mass transport near the surface is slower than surface reaction, dissolution in the channels is transport‐controlled and the original rough channels are smoothed and flattened (Noiriel & Soulaine, 2021; Roded et al., 2020; You & Lee, 2021). When transport near the surface is faster than surface reaction, reaction‐controlled dissolution will preserve the original channel geometry (Roded et al., 2020). Although these studies have focused on the evolution of surface morphology with different surface reaction rates, the interplay between the channel dissolution and the velocity evolution is not well understood.…”

Wormholing in Anisotropic Media: Pore‐Scale Effect on Large‐Scale Patterns

“…Then, following the dissolution in each timestep the geometrical properties are updated (see e.g., Bekri et al., 1995; Detwiler & Rajaram, 2007; Lichtner, 1991). Below, the PNM and main equations are succinctly described; for detailed description see in the SI and previous works (Budek & Szymczak, 2012; Roded et al., 2020).…”

Dissolution Hotspots in Fractures

“…Much attention has been focused on the dynamics of dissolution processes in Hele‐Shaw cells (parallel plates) or in porous media (Daccord, 1987; Fu et al., 2015; Golfier et al., 2002; Jiménez‐Martínez et al., 2020; Ladd et al., 2020; Roded et al., 2020; Song et al., 2014; Szymczak & Ladd, 2011b), which provides insights into the formation of dissolution patterns. Generally, for a slow flow rate, the acid is consumed entirely before invading farther, producing compact dissolution.…”