Enhanced oil recovery uses various techniques to boost oil production from older reservoirs, in which a significant amount of oil remains trapped inside the porous rock. One approach, called polymer flooding, injects long-chain polymer solutions to push the oil towards a production well.
A simple experimental model of polymer flooding, reported in Physics of Fluids, uses particle image velocimetry to better understand the physics behind the process, focusing on measurements of viscoelastic fluid flow through a pillared microchannel.
According to co-author Johan Padding, the inherent difficulty in studying flow inside actual porous rock led his team to create an artificial porous medium, made by placing an array of cylindrical pillars in a microfluidic channel. They investigated flow of both Newtonian and viscoelastic fluids through the channel with microparticle image velocimetry, measuring the velocity field with a spatial resolution of several micrometers.
By changing the flow rate, the researchers tested different Deborah numbers (De), which represent the polymer’s relaxation relative to a characteristic time scale of the flow, while keeping the Reynolds number low (< 0.01). After a critical De, the flow becomes asymmetric while the elastic instabilities remain localized. With even higher De, flow starts to change from one pillar lane to another in an extreme sideways motion. Padding notes that these effects, caused by the elasticity of the polymer fluid, were much stronger than they had anticipated.
The Newtonian fluid, on the other hand, did not show such flow instabilities. The results suggest the mechanism behind enhanced oil recovery is a microsweep of oil droplets by strong elastic instabilities. Next, the researchers aim to investigate the impact of pore porosity, tortuosity and surface interactions.
Source: “Lane change in flows through pillared microchannels,” by S. De, J. van der Schaaf, N. G. Deen, J. A. M. Kuipers, E. A. J. F. Peters, and J. T. Padding, Physics of Fluids (2017). The article can be accessed at https://doi.org/10.1063/1.4995371.
