Mesoscale Structure of Elastic Turbulence in Porous Media

Polymer solutions are a promising tool for groundwater remediation and enhanced oil recovery (EOR); in some cases, the modified flow allows the flooding fluid to sweep a greater portion of the aquifer or reservoir. This enhanced sweep is believed to be linked to unstable flow observed above a threshold flowrate. However, field applications have been limited because the flow structure is not well understood in porous media. We directly observe the flow of polymer solutions in model porous media using confocal microscopy. However, we find that the flow is not purely chaotic, as is commonly assumed: it can adopt two distinct structures, which switch stochastically. We understand this switching as a dynamic coupling between single-polymer conformations and pore-scale flow. We develop dimensionless criteria to describe the spatial and temporal structure of the flow. Understanding and controlling this structure will be integral in robustly applying polymer solutions to groundwater remediation and EOR.