Visualizing MICP with X-ray μ-CT to enhance cement defect sealing

Concerns about leakage exist when storing fluids like CO2 or natural gas in the subsurface given their potential to damage functional groundwater aquifers or be emitted to the atmosphere. Defects in the cement surrounding the wellbore undermine the integrity of subsurface storage systems. Microbially induced calcite precipitation (MICP) is a technique that uses low viscosity fluids and microorganisms ((similar to)2 mu m diameter) to seal defects like micro-annuli, cracks, and channels in well cement. This study quantified MICP in a cement channel defect using X-ray computed microtomography (X-ray mu-CT). Following control and replicate experiments conducted with a low injection flow rate, and which produced X-ray mu-CT data showing precipitation predominately occurred near the inlet, the injection strategy was modified for a third MICP experiment. The revised injection method used an increased flow rate and more frequent nutrient pulses resulting in 1) fewer calcium media pulses to seal the defect and 2) a more homogeneous distribution of mineral compared to the replicate experiments. Observations made during these experiments will aid in improving the safety and efficacy of subsurface fluid storage systems.