Numerical investigation on the fracture-bridging behaviors of irregular non-spherical stiff particulate lost circulation materials in a fractured leakage well section

Abstract

Particle bridging is considered crucial for controlling fracture leakage. A deep understanding of fracture-bridging behavior determines the correct selection of lost circulation materials (LCMs) for fractured leakage. Existing physical and numerical analyses have failed to fully reveal the process of irregular non-spherical particles flowing into a fracture from a wellbore. To investigate the fracture-bridging process, a coupled computational fluid dynamics-discrete element method (CFD-DEM) simulation model was established in this study. The model was verified with a published fluidized bed case and visual fracture bridging simulation experiments. Using digital image technology, 3D discrete element particle models were regenerated from the actual irregular non-spherical stiff particulate LCMs. This allows the analysis of particle size conditions under which particles of different shapes can effectively enter the fractures. The concept of bridging capacity was defined to quantitatively evaluate the bridging effect of LCMs. Based on the numerical simulation results, the bridging patterns of LCM particles were systematically analyzed. The results show that the more uniform the size in each direction of a particle is, the easier it is to enter the fracture. The flatter the particle, the smaller the equivalent particle diameter allowed to enter the fracture. The bridging capacity of irregular blocky particles reached its maximum when the ratio of the particle size to fracture opening was 0.5–0.7. Compared with the blocky particles, flaky particles in fractures exhibited a lower bridging capacity. The bridging pattern of irregular blocky particles in the fracture was single-particle bridging, and the flaky particles had both single-particle and dual-particle bridging patterns. The method and finds proposed in this paper can explain the difference of bridging behaviors of particles with different shapes on the particle scale, and provide a scientific basis for the selection of LCMs in a fractured leakage well section.