Transitions of Dissolution Patterns in Rough Fractures

Abstract

AbstractRock fractures are ubiquitous in geological systems and usually provide dominant pathways for fluid flow in fractured reservoirs. When the flowing fluid is reactive, fracture dissolution expands the aperture and forms various dissolution patterns that amplify the pathways. Previous works focused on the dissolution processes in Hele‐Shaw cells (parallel‐plate) and porous media, but the transitions of dissolution patterns in radial rough fractures are not well understood. Here we combine flow‐visualization experiments with theoretical analysis to elucidate the transitions of dissolution patterns under various flow‐rate and reaction‐rate conditions. We observe and quantify three distinct dissolution morphologies as compact, wormhole, and uniform patterns. We show that the critical Péclet numbers, corresponding to the transitions from compact to wormhole and to uniform patterns, increase with the reaction rate. Based on the growth of dissolution channels in the flow and transverse directions, we establish a theoretical model that describes the transitions of these three distinct dissolution patterns. The phase diagram predicted by the model exhibits good agreement with our experimental results and also well captures the pattern transitions reported in the previous studies. This work improves the understanding on how fracture aperture expands in the dissolution processes that lead to various dissolution channels. Our work is also critical for controlling the fluid flow behavior in dissolving natural rock fractures in subsurface flow systems.