Elastic Turbulence is Spatially Patchy in 3-D Porous Media

Polymer solutions are often injected in porous media for applications such as oil recovery and groundwater remediation. As the fluid navigates the tortuous pore space, elastic stresses build up, causing the flow to become unstable at sufficiently large flow rates: a phenomenon often known as “elastic turbulence”. However, what physical factors determine the onset of this instability, and what its spatial and temporal characteristics are, remain unknown. Here, we use direct visualization in model three-dimensional porous media to address this gap in knowledge. We show that the onset of unstable flow in each pore is akin to a second-order phase transition, arising due to the persistence of discrete patches of instability. Thus, unstable flow is patchy across the different pores of the medium. Guided by these findings, we directly link the energy dissipated by pore-scale fluctuations to the flow resistance through the entire medium, enabling prediction of the macroscopic transport behavior. Together, these results reveal the rich array of behaviors that can arise during the unstable flow of polymer solutions through porous media, and provide a general framework by which flow fluctuations can be predicted and controlled.