Direct Pore-Scale Numerical Simulation of Microbially Induced Calcium Carbonate Precipitation

Microbially induced calcium carbonate precipitation (MICP) is a promising method for eco-friendly solutions in geotechincal engineering. MICP involves highly coupled processes in geochemistry and bacterial metabolism that take place in a porous medium. Advancement of these processes drives calcite crystal growth which leads to a decrease in porosity and permeability of the medium. Mathematical models are being developed and used to predict the fate of system at different conditions. Micro-scale and local bio-geochemical evolution and its role on the overall macroscopic fate of MICP needs further investigation. In this work, a pore-scale reactive transport model of MICP for biocementation is developed in a closed system. MICP is simulated in a sample porous geometry in 2D using a native geochemical solver and a lattice Boltzmann solver that handles diffusive transport. We present reactive-transport factors to up-scale pore-scale effects and quantify the efficiency of MICP at different stages of the process. Our results show that pore-scale effects on the average concentration of urea and calcium are not significant after the initial 20% of urea have been consumed. On the other hand, the pH evolution in the system is significantly affected by pore-scale effects. We also explored effects of biomass density and biomass distribution on the reactive transport factors, as well as the effect of the urea to calcium ratio on the resulting crystallization patterns. We found that a higher ratio of rate of ureolysis to rate of precipitation leads to more nucleation sites and more uniform calcite precipitation in the geometry.