Non-Newtonian rheology is widely acknowledged in subsurface fluids, yet its presence and effects are largely ignored in current fracture-flow studies. Here, we simulate fracture flow of non-Newtonian polymer solutions on a several metre-wide millimetre-aperture network of fractures, examining the complex interplay between fluid rheology, fracture geometry, and fluid inertia. Non-Newtonian fluid characteristics, including a yield stress and shear-thinning behaviour, are modelled using the Herschel-Bulkley-Papanastasiou approach. For the investigated flow rates, our Navier-Stokes simulations reveal significant viscosity variations, resulting in complex flow patterns at both aperture- and network scale. At low rates, non-yielded fluid forms rigid zones occupying up to of the network cross-sectional area, reducing fracture flow connectivity. At high rates, shear-thinning promotes inertia-dominated flow with circulations near fracture intersections. Regarding flow partitioning, yield stress confines flow to dominant pathways while shear-thinning promotes a broader fluid distribution as compared with a Newtonian fluid. Observed multimodal velocity distributions and nonlinear pressure drop-flow rate relationships underscore that fluid rheology must be considered during fracture-flow modelling. • First simulations of non-Newtonian fluid flow in natural fracture networks. • Network geometry drives shear variations, causing viscosity contrasts. • Yield stress causes rigid blockages, enhancing flow localisation. • Shear-thinning increases network flow connectivity. • Fluid rheology fosters multimodal velocity distributions.
Bui et al. (Sun,) studied this question.