Reactive Crystallization in Unsaturated Porous Media

Abstract Crystal nucleation and growth reshape the mechanical, transport and reactive properties in subsurface porous media. We visualize CO 2 hydrate formation and growth in a microfluidic unsaturated porous medium and uncover novel multiscale dynamics: (a) hydrate crystals preferentially grow in narrower paths and seal low‐permeability regions, despite lower surface energy in wider pathways; (b) explosive crystallization emerges at water‐gas interface when growing crystals touch water pockets, that enables efficient hydrate propagation across disconnected water clusters. These observations are theoretically rationalized. We therefore provide an interpretation of field observations of early stage hydrate enrichment in low permeability zones, and discover a new nucleation propagation mechanism. The mechanism may also emerge in other reactive crystallization in unsaturated media.