We seek fundamental understanding of the intricate coupling between reactive dissolution of a porous media, its hydraulic and reactive properties, e.g. its permeability and bulk rate of reaction.
Reactive transport under stress
: We developed a novel pore-scale model that captures coupling of dissolution and weakening-induced compaction during injection of a reactive fluid into porous media. We use numerical simulations to demonstrate how chemo-mechanical deformation of stressed rocks, namely the coupling of pore opening by dissolution with weakening-induced compaction, inhibits permeability evolution. We show that the underlying mechanism is stress concentration at the undissolved (hence stiffer) downstream region, resulting in a bottleneck effect. At high Damköhler number (Da), stress acts to reduce transport heterogeneity, promoting wormhole competition (see video).
Read more in Earth Planet. Sci. Lett. 2018
Impact of medium anisotropy on dissolution
: We develop a pore network model to expose the evolution of heterogeneous and anisotropic media during dissolution.
In the uniform dissolution
regime (flow faster than reaction, low Damkӧhler number), we show that the dissolution extensively homogenizes the medium and therefore the flow field; this is further enhanced when the surface reaction is transport-controlled—-i.e. when slow diffusion of dissolved ions away from the mineral surface leads to the reduction of the global dissolution rate. Under these conditions, diffusive transport is more effective in narrow channels, which selectively enlarge, leading to an initial steep rise of the permeability which later slows down due to a decrease in reaction rate (Water Resour. Res. 2020
In the wormholing
regime (high Damkӧhler), we find that 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 (Geophys. Res. Lett. 2021