Plugging Performance and Retention Mechanism of Composite Bridging Materials for Water-Based Drilling Fluids in High-Temperature and High-Pressure Fractured Formations

Summary

Lost circulation in fractured formations remains a critical challenge in oil and gas drilling, particularly under high-temperature and high-pressure (HTHP) conditions. For this study, we systematically evaluated the physicochemical properties of commonly used bridging materials and optimized rigid, flexible, and fibrous lost-circulation materials (LCMs) suitable for HTHP fractured formations. Through HTHP fracture plugging experiments and visualized physical simulation tests, the bridging-and-packing plugging mechanism of rigid particles, the deformation-accumulation and destabilization behavior of flexible particles, and the synergistic plugging mechanism of rigid, flexible, and fibrous materials were elucidated. Furthermore, composite plugging formulations were optimized for fractures of varying widths. The results demonstrate that marble exhibits optimal thermal stability and compressive resistance, with a crushing percentage of merely 4.5% under 180°C/20 MPa. Among flexible materials, chloroprene rubber demonstrates the best temperature tolerance, with a thermal decomposition temperature ranging from 330°C to 487°C. Regarding fibrous materials, polypropylene fibers exhibit superior dispersion stability, with a turbidity reduction of approximately 25.9% after static settling for 60 minutes. Rigid particle plugging adheres to the “one-third bridging rule,” wherein coarse particles preferentially bridge at fracture entrances, while fine particles tend to plug within the fracture interior. Flexible particles achieve sealing through deformation, filling, and agglomerative packing. Fibers function as spatial network-forming and tensile reinforcement elements. The synergistic interaction among these three components enhances the pressure-bearing capacity and plugging efficiency of the plugging layer. For 2-mm fractures, the optimized formulation (7.0% marble + 3.0% chloroprene rubber + 0.5% polypropylene fiber) achieves a pressure-bearing value of 12.76 MPa, with sealing accomplished within 42 seconds. Furthermore, the optimized formulations for the tested discrete fracture widths of 1  mm, 2  mm, 3  mm, and 5  mm all exceeded 10 MPa in pressure-bearing capacity, demonstrating good adaptability within the present test range. This study provides both mechanistic insights and practical formulation guidelines for bridging plugging in HTHP fractured formations.