Mechanism of Dynamic Deformation in Stress-Sensitive Fractures and Adaptive Plugging Formulation Development

Abnormal fluctuation in wellbore pressure and formation pressure during drilling operations can easily induce complex and dynamic morphologies of stress-sensitive fractures, severely compromising the pressure-bearing capacity of plugging zone. This phenomenon leads to repetitive fluid loss and other complex downhole accidents. By focusing on the dynamic deformation behavior of stress-sensitive fractures, this study analyzed the characteristics of rough fracture opening and closure deformation based on fracture mechanics theory. A 3D model was developed to simulate stress-sensitive fractured formation, revealing that rough fracture deformation progresses through three stages: the initial stage, the localized deformation stage, and the overall deformation stage. The findings indicate a power-law relationship between dynamic fracture width and fracture contact surfaces. Novel plugging formulations were developed to adapt to fracture deformation under dynamic condition, validated through laboratory experiments. Additionally, the impact of material size, shape, and concentration on the plugging efficacy were systematically investigated. Through these evaluations, optimal plugging formulations were achieved. Experimental results demonstrated that conventional bridging materials can sustain a pressure-bearing capacity of less than 4 MPa under 20.7% fracture deformation when plugging two millimeter wide fractures. In contrast, the adaptive formulation maintains a pressure-bearing capacity of 4 MPa but under 68% deformation. These insights contribute significantly to the optimization of loss control slurry formulations for fractured formations.