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

The formation of dissolution conduits by focused reactive flow (i.e., wormholing) in anisotropic media is studied using a pore network model. Simulations reveal a significant effect of anisotropy on wormholing dynamics and medium permeability evolution. Particularly, anisotropy controls wormhole competition and their characteristic spacing. It also affects the flow through the individual wormholes and their shapes, and consequently, shifts the optimum injection rate at which breakthrough is achieved at a minimal expense of reactant. For anisotropic media with low transverse pore conductivities, wormhole distribution ceases to be scale-invariant and pronounced side-branches develop. Wormholing is further compared to viscous fingering in an anisotropic network, and other unstable growth processes of similar underlying dynamics. Despite several similarities, few important differences are identified. Our findings contribute to the understanding of wormholing in geological media and demonstrate how pore-scale features can fundamentally affect the emergence of large-scale morphologies.