Flow induced viscoelasticity in fractures

•Flow behaviour of VES fluids in conduits is investigated with PIV.•VES fluids in slits show non-linear and size dependent pressure-flow responses.•At low fluid velocities VES fluid can show linear rheology in conduits.•Above a critical wall shear rate the fluid shows a high and varying viscosity.•Transitional fracture flow characteristics can be estimated using rheometer data.

The behaviour of viscoelastic surfactant solutions under pressure driven flow in fractures is studied with particle image velocimetry. We demonstrate that flow is selectively retarded in larger conduits and we zoom in to smaller scales in order to distinguish local flow resistance effects. At low velocities in the conduit, the viscosity is low and relatively constant giving a quasi Hagen-Poiseuille profile. At higher velocities, enhanced aperture size dependent viscosities are obtained. The different flow characteristics enable size selective retardation. This can be attributed to shear rates in larger fractures which extend into the viscoelastic enhancement regime associated with shear induced structures.