Mechanism of anomalously increased oil displacement with aqueous viscoelastic polymer solutionsElectronic supplementary information (ESI) available: Details of core flooding experiments, details of polymer solution preparation, details of microfluidic networks, PIV images and experimental detail expanding on Fig. 3, videos from which images of Fig. 4 were derived and solution rheology for materials in Fig. 4. See DOI: 10.1039/c5sm00064e

Single-phase flows of viscoelastic polymer solutions in both microfluidic devices and rock cores exhibit apparent flow thickening. We demonstrate that this thickening occurs above a critical Deborah number corresponding to the onset of spatio-temporal fluctuations. These fluctuations are observed to occur over a broad range of spatial and temporal scales consistent with elastic turbulence. The fluctuations provide a previously unreported mechanism for enhancing the displacement of a second, capillary trapped, immiscible phase. Flows of viscoelastic polymer solutions in porous media exhibit elastic turbulence that destabilises and displaces trapped oil.