Microscale insights into enzyme-induced carbonate precipitation in rock-based microfluidic chips

Biomineralization technology shows promise for sealing subsurface fractures, but understanding its microscale mechanisms in real rock fractures remains incomplete. This study utilized a microfluidic chip incorporating real rock slices to conduct enzymatically induced carbonate precipitation (EICP) experiments using one-phase continuous injection strategy. Real-time observations revealed gray flocs forming and clustering into aggregates susceptible to transport by flow. CaCO₃ crystals formed on rock and PDMS surfaces effectively filled and bridged fractures, leading to a significant pressure drop. Rough surfaces can provide additional sites for solute attachment and CaCO3 heterogeneous nucleation. High velocities and small apertures generally promoted floc formation and reduced crystal growth. Precipitation content gradually increased with a decreasing rate. Lower estimated precipitation efficiency was obtained in smaller, high-flow fractures. Precipitates on rock interfaces induced eddies and significant pressure drops within narrow pore throats. Crystal growth displayed a two-stage development: an initial increase followed by a decrease, varying across different facets (the surfaces or orientations of the growing crystals). Growth competition will occur when two or more neighboring crystals come into contact with diverse grain orientations. The findings provide valuable microscale insights into microscale processes governing EICP within real-rock fractures, contributing to evaluate its efficacy in subsurface fracture sealing applications.