  The current conceptual model of mineral dissolution in porous media is
comprised of three dissolution patterns (wormhole, compact, and uniform) - or
regimes - that develop depending on the relative dominance of flow, diffusion,
and reaction rate. Here, we examine the evolution of pore structure during acid
injection using numerical simulations on two porous media structures of
increasing complexity. We examine the boundaries between regimes and
characterise the existence of a fourth regime called channeling, where already
existing fast flow pathways are preferentially widened by dissolution.
Channeling occurs in cases where the distribution in pore throat size results
in orders of magnitude differences in flow rate for different flow pathways.
This focusing of dissolution along only dominant flow paths induces an
immediate, large change in permeability with a comparatively small change in
porosity, resulting in a porosity-permeability relationship unlike any that has
been previously seen. This work demonstrates that our current conceptual model
of dissolution regimes must be modified to include channeling for accurate
predictions of dissolution in applications such as geologic carbon storage and
geothermal energy production.
