Experimental Study on the Evolution of Flow Channels and Precipitation Characteristics in Microbially Induced Fracture Biomineralization

In this study, a microbially induced calcium carbonate precipitation (MICP) technique has been proposed as an alternative to traditional cementitious strategy for filling rock fractures to improve rock strength and reduce permeability. We investigate calcium carbonate (CaCO3) precipitation characteristics and flow channel evolution within artificial fractures treated with MICP to gain insights into the fundamental mechanisms underlying microbially induced mineralization in rock fractures with varying initial apertures and joint roughness coefficients. CaCO3 precipitation occurs within small-scale artificial fractures, which are formed by a transparent polymethyl methacrylate top plate and either a smooth or rough acrylonitrile butadiene styrene base plate. The evolution behavior of the flow channels is captured—both temporally and spatially—by using a high-resolution camera employing time-lapse photography, and the spatial distribution of CaCO3 precipitation throughout the base plate is accurately quantified by using a three-dimensional laser scanner. The results reveal that in the smooth fracture, the yield and distribution ranges of the biomineralization products increase as the aperture increases and gradually stabilize at the critical aperture. Two critical aperture intervals (referred to A and B) are identified under a constant staged injection strategy: 1.4–1.5 and 1.1–1.2 mm, respectively. The rate and efficiency of CaCO3 precipitation experience significant changes when the fracture aperture is outside the aforementioned two intervals. Within the rough fracture, the convex–concave structure simulating rough fluctuations of the fracture surface distributed on the base plate significantly facilitate the precipitation of CaCO3 on its surface. An interesting observation is that the flocs in the suspension transport stage can be impeded by gas bubbles; therefore, the location of CaCO3 precipitation could be controlled to some extent by changing the location of the gas bubbles incorporated during precipitation, indicating the potential of gas bubbles as nucleation sites to promote CaCO3 crystallization. The transport and settling of flocs, as well as the formation, clogging, and unclogging of flow channels, are explained at the microscopic level.