Abstract

A reactive fluid flowing through a porous or fractured rock and dissolving the rock matrix may trigger an instability, leading to spontaneous formation of pronounced channels or wormholes. I will present a linear-stability analysis of this system and show that there are two different instabilites. One is associated with an initial uniform-porosity state and the other with a steadily propagating one-dimensional dissolution front. I will discuss the origin of both instabilities and the physical conditions under which they can be observed. In particular, it is argued that the former ‘initial- state’ instability is relevant to the dissolution of fractures in carbonate rocks, giving rise to the formation of limestone caves. Finally, I will discuss the later stages of the system evolution, when the channels interact, competing for the available flow; eventually the growth of the shorter ones ceases. This leads to self-similar patterns of growth, with the flow becoming concentrated within a few active channels.