Hydrodynamic Limitations on Biomineralization-Induced Permeability Reduction

While the subsurface applications of microbially induced carbonate precipitation (MICP) have so far emphasized near-wellbore permeability reduction, MICP technology may eventually be expanded to support needs as diverse as thief zone remediation in geothermal reservoirs or caprock sealing in CO2 sequestration sites. For these applications to be realized, however, there is a need to understand whether permeability reduction can be achieved under the high flow velocities that may occur, for example, in zones of locally high permeability or along preferential flow paths. In this study, bioaugmented MICP is applied to three natural limestone cores of similar porosity but differing pore size distribution. The injection strategy includes biomass attachment and growth phases before mineralization, with the goal of separating the effects of each phase on permeability. In order to test the resilience of biomass and precipitate accumulation against flow-induced shear stress, saline solution is injected intermittently at a faster flow rate. Real-time permeability estimates show that biomass accumulation reduces permeability even without mineralization, although biomass accumulation may ultimately be shear-limited. Calcium mass balances suggest that sloughing of precipitates is also possible, though its effect on permeability depends on whether mobilized precipitates induce clogging or are transported out of the core. X-ray computed microtomography imaging of the cores suggests that when flow rates are moderate and preferential flow paths do not dominate flow, precipitates tend to accumulate preferentially in larger pores, yielding controlled, incremental permeability reduction. These findings lay essential groundwork toward refining MICP models to account for spatial heterogeneities in the subsurface.