Abstract To investigate the migration and placement patterns of low-density proppants within fractured deep complex coal seams, a visualised branching fracture simulation apparatus was constructed using glass microspheres as proppants. Migration simulation experiments were conducted with variables including proppant particle size, concentration, delivery rate, and fracturing fluid viscosity. Results indicate that larger-sized 250/550μm glass microsphere proppants enhance near-end fracture filling, while smaller 120/160μm proppants improve far-end filling. The 160/250μm proppant exhibits overall uniform distribution. As proppant concentration increased from 2% to 10%, both the equilibrium height and length of sand ridges within each fracture steadily increased. Higher concentrations improved fracture filling; at 10% concentration, both primary and secondary fractures exhibited satisfactory filling. Within the primary fracture, placement coverage gradually decreased with increasing flow rate. The 3.0 L/min group exhibited the most uniform overall placement, providing effective support across all fracture levels. Glass microspheres, being lightweight and highly spherical, can be delivered to distal fractures with appropriately increased flow rates. However, excessively high flow rates lead to uneven filling of primary and secondary fractures. As viscosity increased, the enhanced fluid load-bearing capacity enabled glass microsphere proppants to migrate further. In the experiments, the 5 mPa·s viscosity group demonstrated the most favourable overall results.
Ni et al. (Mon,) studied this question.