Shear‐Thinning Rheology Reshapes Hydrodynamic Dispersion in Heterogeneous Fractures

Abstract

Hydrodynamic dispersion of shear‐thinning fluid in fractured rocks is jointly governed by fracture heterogeneity and fluid rheology, yet the way aperture correlation length alters dispersion mechanisms remains unclear. Here, we carry out pore‐scale lattice Boltzmann simulations to investigate fluid flow and solute transport in heterogeneous fractures with systematically varied aperture correlation lengths and injection velocities. The results show that aperture correlation length controls the basic transport pattern, with short correlation length leading to diffusive front spreading and long correlation length promoting channelized transport through persistent preferential pathways. Increasing injection velocity drives the transition from molecular diffusion to advective transport, in which the overall solute spreading reflects the competition between fracture‐plane geometrical dispersion and aperture‐scale shear dispersion. Shear‐thinning rheology reshapes this progression by enhancing fracture plane velocity heterogeneity while reducing aperture‐wise velocity gradients, thereby extending the role of geometrical dispersion and delaying the development of shear‐dispersion. Pore‐scale analysis further suggests that shear‐induced viscosity reduction promotes earlier eddy formation in stagnant zones and alters local mixing processes beyond purely diffusion‐controlled exchange. These findings provide a pore‐scale mechanistic explanation for the transition and reorganization of dispersion regimes in heterogeneous fractures.