Radial migration behavior of particles in rough fracture wedge-shaped spaces

Existing research rarely considers the rough surface morphology of natural fractures and the radial migration of particles within the fractures along with their plugging behavior simultaneously. This study innovatively establishes a radial wedge-shaped flow space model of rough fractures using numerical fracture surface synthesis techniques. The computational fluid dynamics-discrete element method was used to simulate the radial migration, bridging, and plugging processes of particles under different factors. The results show that the size of rock samples does not constrain the high-precision digital reconstruction method for fractures. It can be adjusted to the appropriate size according to research needs. In rough fractures, the radial migration of particles exhibits strong disorderliness, with high probabilities and intensities of particle collisions, making effective plugging rather challenging. In contrast, within flat wedge-shaped fractures, forming annular plugging zones at different locations for particles of varying sizes, thus achieving higher plugging efficiency. When drilling encounters high-angle or vertical fractures in straight wells, linear flow tends to occur. However, when encountering nearly horizontal fractures, radial flow prevails more often, causing significant disturbances between streamlines in local areas. Higher-viscosity fluids exhibit poorer mobility, which delays the timing of particle bridging and plugging. Additionally, the reduced fluid mobility lessens the disordered movement of particles within the fracture, thereby decreasing the intensity of particle collisions. Excessively low fluid pressure results in insufficient driving force for particle migration, thereby failing to plug the fractures effectively. This research provides new insights into the mechanisms of fluid loss during deep shale gas development and potential control strategies.