Microbially induced carbonate precipitation (MICP) is an emerging and promising approach for mitigating leakage in tunnel engineering. However, a comprehensive understanding of its sealing mechanisms in natural fractures under deep geological conditions remains insufficient. In this study, eight rough fracture samples with different roughness levels were prepared and a two-stage injection method was executed under simulated geological conditions (8 MPa confining pressure and 55 °C temperature). A self-developed multi-field coupling experimental system was employed to monitor the real-time changes in injection pressure and permeability. Additionally, 3D scanning and grayscale image analysis were utilized to quantitatively characterize the distribution of CaCO₃ precipitation. This study uniquely reveals the stage-dependent evolution of MICP sealing behavior in natural rough fractures under deep geological conditions. It further clarifies, for the first time, the dual regulation of fracture roughness on sealing efficiency under varying injection pressures. The results indicate that the sealing process in fractures with high roughness (JRC ≥ 5.33) follows a distinct three-stage evolution: the initial rapid sealing stage (I), followed by the dynamic equilibrium stage (II) and the secondary strengthening stage (III). In stage II, local erosion led to permeability fluctuations (± 30%), prolonging the sealing duration by approximately 60%. The study further reveals a dual-stage regulation of fracture roughness on sealing performance: under low pressure ( 1 MPa) it exacerbates erosion effects and consequently delays sealing. A semi-empirical permeability equation based on injection pressure (P) was developed to evaluate sealing effectiveness. Image analysis additionally clarifies the impact of roughness on the spatial distribution of CaCO₃ precipitation. These findings enhance the understanding of the coupled influences of fracture roughness and injection pressure, offering practical guidance for optimizing MICP operations in deep subsurface fractures.
Song et al. (Mon,) studied this question.