A bio-healing method for underground long rock fractures with high bridging rate

One of the key challenges for underground rock reservoirs is ensuring prevention of the unwanted fluid leakage through rock fracture networks during their service life. Microbial-induced calcium carbonate precipitation (MICP) technology has emerged as a promising bio-healing method for rock fractures with small apertures. In this study, a new “three-stage” injection strategy-based MICP (TS-MICP) bio-healing method was proposed, aiming to achieve a “three-high” performance that includes high bridging rate, high mechanical strength, and high homogeneity. A series of meter-scale rock fracture models were prepared to conduct TS-MICP grouting tests. Compared with the traditional injection strategy-based bio-healing methods, the TS-MICP method significantly improved the bridging rate (32.1%–89.5%), mechanical properties (0.138–1.023 MPa), and homogeneity of CaCO 3 precipitation (334.4%). Additionally, it achieved a higher material utilization rate (1.72 times higher), reducing the consumption of cementation solution (CS) by 258.8%, thereby demonstrating greater potential for field applications. The underlying mechanism for achieving high bridging rate and high homogeneity in CaCO 3 precipitation can be attributed to the synergistic effects of the coupling injection strategy, which optimizes the advantages at each stage. In stage I, under the influence of gravity, the rapid flocculation and hydrogen bonding interactions of organic matter lead to formation of the dense and high-strength CaCO 3 precipitation at the bottom using a low-concentration bacterial suspension (BS). This process establishes bridging steps along the wall sides for subsequent uniform CaCO 3 precipitation. In stage II, concentrated BS is utilized to produce looser CaCO 3 flocculation, which precipitates uniformly on the pre-existing bridging steps. In stage III, a two-step injection strategy was employed to reinforce the loose CaCO 3 crystals formed in stages I and II, and finally forms a strong bridging effect with “three-high” performance.