NMR Measurements of Fractured Sandstone Sealed with Microbially Induced Calcium Carbonate Precipitation: Hydraulic Properties and Cementation Distribution

Microbially induced calcite precipitation (MICP) is an emerging ground improvement method. Although a reduction in permeability of intact and fractured rock is reported due to MICP, the heterogeneous distribution of the calcium carbonate precipitation and clogging near the injection source have posed challenges to using this technique in underground applications. Monitoring tools that characterize the precipitate distribution may be used to mitigate heterogeneity. This study investigated the effect of inoculation and incubation conditions on sealing fractured sandstone following a staged injection strategy. Nondestructive and noninvasive nuclear magnetic resonance (NMR) methods that are suitable for subsurface application were employed to monitor changes in pore structure and fracture aperture during the MICP process. The results showed that the staged injection strategy resulted in a uniform precipitation distribution along the fractures regardless of inoculation and incubation condition. Though the sensitivity of NMR was lower than that of gas expansion and conventional gravimetric methods, NMR was demonstrated to be a reliable tool for monitoring precipitation distribution. This study promotes MICP as a promising biotreatment that could advance underground engineering.