Characterizing Permeability Evolution During Self-Sealing in Kaolinite Mudrocks Using a Bi-Exponential Model

Fracture self-sealing in clay-rich mudrocks plays an important role in controlling fluid migration in subsurface engineering and geoenergy applications, yet the factors governing permeability reduction remain difficult to quantify in a unified manner. In this study, laboratory experiments were performed on synthetic kaolinite-based mudrock specimens to investigate fracture permeability evolution under controlled effective stress, overconsolidation ratio (OCR), and pore-fluid conditions. Artificial fractures were introduced into resedimented specimens with prescribed stress histories, and permeability evolution was monitored during sealing of the fracture. A phenomenological bi-exponential model was employed to quantitatively describe the observed permeability reduction, separating the contribution of rapid mechanically driven closure and slower time-dependent sealing behavior. The results showed that increasing effective stress accelerates permeability reduction, while higher OCR suppresses late-time sealing under identical current stress. Pore-fluid composition further altered the sealing behavior, with brine-saturated fractures exhibiting stronger permeability reduction than oil-saturated fractures. Additional experiments showed that the model parameters evolve over time, reflecting the intrinsically time-dependent and non-linear nature of the self-sealing response. These results provide a practical framework for systematically interpreting fracture self-sealing behavior in low-swelling clay systems relevant to subsurface sealing and geoenergy operations.