Hydrodynamic coupling in microbially mediated fracture mineralization: formation of self-organized groundwater flow channels

Evidence of fossilized microorganisms embedded within mineral veins and mineral-filled fractures has been observed in a wide range of geological environments. Microorganisms can act as sites for mineral nucleation and also contribute to mineral precipitation by inducing local geochemical changes. In this study, we explore fundamental controls on microbially induced mineralization in rock fractures. Specifically, we systematically investigate the influence of hydrodynamics (velocity, flow rate, aperture) on microbially mediated calcite precipitation. Our experimental results demonstrate that a feedback mechanism exists between the gradual reduction in fracture aperture due to precipitation, and its effect on the local fluid velocity. This feedback results in mineral fill distributions that focus flow into a small number of self-organizing channels that remain open, ultimately controlling the final aperture profile that governs flow within the fracture. This hydrodynamic coupling can explain field observations of discrete groundwater flow channeling within fracture-fill mineral geometries where strong evidence of microbial activity is reported.