Inertia-driven particle dynamics across rock fracture intersection: Experimental insights into transport mechanisms

Particle-laden fracture flows are vital in many subsurface engineering applications, including hydrocarbon extraction, geothermal energy recovery, carbon dioxide and hydrogen storage. Fluid inertia and intersection-driven turbulence critically govern particle transport at fracture intersections, yet the underlying mechanisms remain poorly characterised, particularly in time-dependent, spatially heterogeneous conditions representative of subsurface reservoirs. This investigation provides the first time-resolved experimental characterisation of inertia-driven particle dynamics at fracture intersections, employing time-resolved particle tracking velocimetry (PTV) to investigate fluid and particle velocity fields simultaneously across a metre-scale fracture intersection. Results reveal that fluid inertia controls the Reynolds-number-dependent shifts in turbulence modulation. At low-to-intermediate velocities (Re ≤ 4000), particles attenuate carrier-phase turbulence across all frequencies while exhibiting orders-of-magnitude amplification at low frequencies ( f < 10 Hz). At higher velocities (Re ≥ 8000), particle wakes generate extreme local particle Reynolds numbers (Re p = 350–600), injecting turbulent kinetic energy across broad frequency bands and augmenting carrier-phase turbulence. Frequency-selective particle-fluid coupling emerges, wherein particles respond to large-scale intersection-vortices ( f < 10 Hz) while decoupling from high-frequency fluctuations ( f > 50 Hz). At high turbulence, collision-driven coherence enhancement maintains particle trajectory persistence through collision-organised collective motion rather than randomisation. Intersection-generated vortices function as dynamic particle routers, actively driving cross-branch transport through circulation-mediated pathways and contradicting conventional “dead zone” interpretations. These findings establish that fluid inertia governs particle distribution through vortex-mediated spatial organisation, frequency-dependent coupling, and collision-enhanced coherence, necessitating intersection-resolved modelling frameworks for accurate prediction of particle placement in complex fracture networks. • First time-resolved PTV capturing inertia-driven particle dynamics within fractures. • Fluid inertia reverses turbulence modulation from attenuation to augmentation. • Intersection vortices route particles dynamically contradicting dead-zone assumptions. • Collision-enhanced coherence maintains trajectory persistence at high turbulence. • Accurate particle-flow predictions must incorporate time-dependent inertial effects.