Influence of injection methods on bio-mediated precipitation of carbonates in fracture-mimicking microfluidic chip

Enzymatically induced carbonate precipitation (EICP) is a potential method to alter the hydraulic properties of fractured rocks. The pore-scale in situ formation of bio-mediated precipitated carbonates in fracture-mimicking channels was investigated experimentally through a visualisation platform and microfluidic technology. Image processing was employed to analyse the precipitation behaviour. Three representative biogrouting methods (one-phase continuous injection, one-phase staged injection and two-phase staged injection) and the role of nucleation agents were examined in this study. Results revealed that more amorphous substances formed during the one-phase injection process, and the one-phase staged injection method exhibited superior precipitation efficiency, whereas the two-phase staged injection method demonstrated better effectiveness in channel clogging. The addition of nucleation agents resulted in a channel-like precipitation pattern, compared to the formation of more crystals in the absence of additives. The hydrodynamic coupling between precipitation and flow velocity was used to explain the mechanisms of fracture sealing. Precipitation and aggregation led to the reduction in microchannel aperture, thereby influencing the flow field. Under flow-induced shearing, the amorphous substances could be transported and settled on the channel surface, leading to a self-enhancing process in channelling. This study provides insights into the microscopic mechanisms of EICP and advances the application of EICP in fracture repair.