Influence of Fluid Rheology on Fluid Flow in a Natural Fracture Network

TL;DR

This study investigates how non-Newtonian fluid rheology, including yield stress and shear-thinning, influences flow patterns, connectivity, and pressure relationships in natural fracture networks through detailed simulations.

Contribution

It introduces a comprehensive simulation approach for non-Newtonian fluids in fracture networks, highlighting the importance of rheology in flow behavior and network connectivity.

Findings

Non-Newtonian rheology causes significant viscosity variations and complex flow patterns.

Yield stress reduces flow connectivity by forming rigid zones.

Shear-thinning promotes inertia-dominated flow and broader fluid distribution.

Abstract

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 ~65% 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.