Impact of Temperature and Pressure on the Effectiveness of MICP for Shale Fracture Sealing

Microbially induced carbonate precipitation (MICP) has shown great potential for repairing fractures and mitigating leakage risks. Nevertheless, the effects of temperature and pressure remain insufficiently understood. This study evaluated the effectiveness of MICP in shale fracture sealing, with a focus on the influence of aperture, temperature and pressure. The experimental findings indicate that temperature and pressure exerted dual effects on the MICP sealing process. On one hand, high temperature and high pressure (55 °C, 7.5 MPa) suppressed bacterial activity, thereby inhibiting calcium carbonate formation and resulting in a permeability reduction that was one order of magnitude less in Test HT compared to Test AT. On the other hand, calcium carbonate crystals formed under these conditions exhibited enhanced mechanical strength, which became particularly crucial when calcium carbonate content exceeded 40%. The results also showed that the permeability of the shale fracture samples decreased by one to three orders of magnitude after seven treatment cycles. This reduction was more pronounced in fractures with smaller apertures, especially those below 0.3 mm. For specimens with fracture apertures below 0.7 mm, the splitting tensile strength of the repaired samples ranged from 80 to 600 kPa, with corresponding breaking strains between 0.6% and 1.2%. A negative exponential relationship was observed between fracture aperture and splitting tensile strength. This study provides a systematic experimental evaluation of MICP-based shale fracture sealing under coupled temperature-pressure conditions, and reveals the dual role of high temperature and high pressure in inhibiting calcium carbonate precipitation while enhancing the mechanical contribution of the formed carbonate crystals.