Analysis of particle transport mechanism and factors influencing sealing effect in fractured strata

Severe fluid loss in fractured formations poses a major technical challenge in deep oil and gas drilling, significantly constraining wellbore integrity and drilling efficiency. This study establishes a comprehensive multi-scale research system combining indoor experiments and CFD-DEM numerical simulations to investigate particle transport and sealing mechanisms. A dynamic sealing model incorporating the Di Felice drag force and modified JKR contact theory was innovatively developed to rigorously analyze multi-physics interactions, including van der Waals forces, electrostatic forces, and fluid shear under complex seepage conditions. Results demonstrate that for single-particle sealing, the optimal particle size is 1/2 to 2/3 of the fracture width, satisfying the one-third bridging theory. Among gradation schemes, a triple-particle distribution exhibits the highest pressure-bearing capacity, particularly when dominant particles comprise 70%–80% and the filling particle size ratio is 0.2–0.4. Furthermore, an optimal concentration window of 8% was identified; lower concentrations result in sealing failure, while higher concentrations cause false plugging due to jamming effects . Additionally, increasing drilling fluid viscosity to 50 mPa · s enhances sealing layer density, while an optimal fluid density of 1.4 g/cm 3 achieves a critical balance between particle accumulation efficiency and buoyancy. With experimental and simulation results agreeing within a 5% relative error, this research provides a robust theoretical basis for optimizing leak-stopping fluid formulations in fractured strata.