Optimization Method for Bridging Particle Size in Fractured-Type Lost Circulation Based on Dynamic Fracture Width

To address the mismatch between plugging particles and dynamic fractures during lost circulation control, based on the 1/3–2/3 bridging rule and considering the amplitude of dynamic fracture width, a reference fracture width for particle size screening was determined, and a mathematical model for optimizing plugging particle size based on dynamic fracture width was established. A stability criterion for key bridging particles was proposed. The factors influencing bridging stability were analyzed, and the plugging capability of the optimized particles was verified through laboratory simulation experiments. The results indicated that when the maximum fracture width increased from 3.5 mm to 4.2 mm, the maximum bridging particle size increased from 1.75 mm to 2.10 mm. The minimum fracture width determined the upper limit of bridging particle size. The bridging particle size increased with increasing maximum fracture width. When the maximum bridging particle size equaled the minimum fracture width, there was a risk of bridging-off. When the dynamic fracture width amplitude exceeded 50%, bridging particles could not form a stable bridge in the fracture, which necessitated alternative lost-circulation techniques. The lost-circulation system optimized based on this model could accommodate a dynamic fracture width amplitude of 37%. In dynamic fracture experiments, the pressure-bearing capacity reached 9.8 MPa, with a cumulative fluid loss volume of 93 mL, demonstrating better plugging performance than those achieved using the traditional static bridging rule. By precisely quantifying particle size under dynamic fracture conditions, this model significantly improves the plugging performance under dynamic fracture conditions and provides a theoretical reference for on-site optimization of lost-circulation material particle size and blending ratios.