Controlled particle migration in non-Newtonian fluids is very important in many biological, environmental and industrial applications like hydraulic fracturing. The phenomenon of particle transport in non-Newtonian fluid is generally governed by complex interplay of different effects like shear-thinning or thickening behaviour of fluid, viscoelasticity and secondary flow. The present literature on the particle migration in a channel shows that particles move towards the centreline in highly viscoelastic fluids at very low Reynolds number (negligible inertial effects) and move away from the centreline in Newtonian fluids. However, very little is known about how flow and particle dynamics is affected in a rock fracture network or porous medium. To obtain insights into flow dynamics in such a complex geometries, we use microchannels with the specific arrangement of pillars in order to mimic the hydraulic fracture network and porous media. In this study, we perform experiments on the migration of non-Brownian particles in such pillared microchannel of different porosities with different types of fluids - Newtonian, shear-thinning and viscoelastic. The comparison of the particle behaviour in these fluids reveals the influence of the viscous and elastic forces on particle migration. In this work, standard micro-PIV technique is used to obtain the fluid velocity and PTV is used to track the particle velocities. This work provides fundamental insight on effect of viscoelasticity on particle migration in a model fracture network/porous media. @en

Polymer liquids are used in the oil industry to improve the volumetric sweep efficiency and displacement efficiency of the oil from a reservoir. Surprisingly, it is not only the viscosity but also the elastic properties of the displacing fluid that determine the displacement efficiency. To understand the effects of viscoelasticity on enhanced oil recovery, both single and multiphase experiments are performed in pillared microchannels of different pitches. Different shear thinning viscoelastic fluids are used to obtain insights into flow structures in these pillared micro channels. Particle image velocimetry (PIV) technique is applied to characterise the complex flow structures at very low Reynolds number (< 0.01). The pressure drop across the channel for a range of Deborah numbers is measured using a pressure sensor. We observe an onset of flow asymmetry for the viscoelastic fluid after a critical Deborah number depending on the channel configuration. This flow asymmetry increases with an increase in Deborah number and shows characteristics of elastic turbulence. This can be characterised by an increase in velocity and pressure fluctuations which has a temporal and spatial dependency. The sudden increase in the velocity fluctuations is also visible from the micro-PIV experiments. Though the fluid is shear thinning in nature, we observe an increase in the apparent viscosity after the critical De number is reached, which represents a thickening behaviour. So strong shear and extensional effects of the viscoelastic fluid are responsible for the asymmetric flow structures. Next we performed multiphase flow experiments, by saturating the microchannel with oil, and then displacing it by different non-Newtonian fluids. Surprisingly we found the enhanced recovery corresponds to the critical De number where the onset of instability initiates for the single phase experiments. The elastic instabilities and the relation to enhanced displacement provides fundamental insights in the mechanism of polymer flooding.@en