Retraction of dissolution front in natural porous media

TL;DR

This paper reveals a surprising retraction of the dissolution front in natural porous media driven by infiltration instability, supported by real-time imaging and simulations, challenging existing assumptions in water-rock interaction studies.

Contribution

It uncovers the spontaneous migration of the dissolution front against flow pressure and links it to surface generation mechanisms, providing new insights into dissolution dynamics.

Findings

Dissolution front can spontaneously retract against flow pressure.

Surface generation significantly influences reactive surface area.

Flow-dependent surface dynamics reconcile field and lab reaction rate discrepancies.

Abstract

The dissolution of porous materials in a flow field shapes the morphologies of many geologic landscapes. Identifying the dissolution front, the interface between the reactive and the unreactive regions in a dissolving medium, is a prerequisite for studying dissolution kinetics. Despite its fundamental importance, the dynamics of a dissolution front in an evolving natural microstructure has never been reported. Here we show an unexpected spontaneous migration of the dissolution front against the pressure gradient of a flow field. This retraction stems from the infiltration instability induced surface generation, which can lead to a reactive surface dramatically greater than the ex situ geometric surface. The results are supported by a very good agreement between observations made with real time X-ray imaging and simulations based on static images of a rock determined by nanoCT. They both show that the in situ specific surface area of natural porous media is dependent on the flow field and reflects a balancing between surface generation and destruction. The reported dynamics challenge many long-held understanding of water-rock interactions and shed light on reconciling the discrepancies between field and laboratory measurements of reaction kinetics.