Study on the Flow and Transportation Law of Glass Beads Proppant in Complex Coal Seam Fractures

Abstract

Abstract. Hydraulic fracturing is the core technology for coalbed methane (CBM) stimulation. However, conventional proppants face significant challenges in transporting through deep, complex fracture networks, making it difficult to effectively support distal regions and branch fractures. This study investigates the transport and placement behavior of low-density glass microsphere proppants in complex coal seam fractures, providing experimental evidence for optimizing deep coal fracturing operational parameters. Based on dual similarity criteria of Reynolds number and Stokes number, a visualized branching fracture simulation apparatus was designed and constructed. Systematic transport simulation experiments were conducted by varying proppant size (120/160, 160/250, and 250/550 μm), concentration (2–10%), injection rate (1.2–4.3 L/min), and fracturing fluid viscosity (1–7 mPa · s). Three quantitative indicators—filling efficiency, equilibrium sand height, and placement area—were employed to evaluate proppant placement performance. Results demonstrate that large-diameter proppants (250/550 μm) rapidly settle in the main and horizontal fractures, forming high sand banks that effectively support near-wellbore regions. Small-diameter proppants (120/160 μm) exhibit superior suspension characteristics, enabling penetration into tertiary fractures and oblique fractures, though near-wellbore support remains insufficient. Medium-diameter proppants (160/250 μm) achieve the most uniform overall distribution. As proppant concentration increases from 2% to 10%, filling efficiency in all fracture levels increases synchronously; at 10% concentration, effective support is achieved in both the main fracture and all secondary branches. An injection rate of 3.0 L/min yields the most uniform placement across all fracture levels; insufficient rates cause excessive accumulation in the main fracture with limited sand entry into branches, while excessive rates result in substantial proppant loss through the outlet and inadequate filling in both primary and secondary fractures. At a viscosity of 5 mPa · s, an optimal balance between near-wellbore settling and distal transport is achieved, yielding the best overall support performance. This study established an experimental methodology for low-density proppant transport in complex fractures under dual similarity criteria, and proposed engineering recommendations including staged injection, pump rate optimization, and viscosity matching, thereby providing quantitative guidance for deep coalbed methane fracturing design.