Flow induced viscoelasticity in fractures

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.