Convective Dispersion in a Real Fracture

Solute transport in fractured rocks is of major interest in many applications: geothermal energy production, petroleum industry, ground water management. This work focuses on a dispersion experiment performed with a transparent replica of a real fracture. The local aperture map was extracted using the well-known Beer-Lambert law, which shows a very heterogeneous medium. The hydrodynamic aperture was determined from single-phase flow measurements by assuming the validity of cubic law. Numerical simulation on the aperture map leads to the same aperture value. A tracer experiment was then performed at a Peclet number high enough to neglect molecular diffusion. While the classical convection-diffusion approach fails to interpret experimental results, a basic model of parallel rectangular ducts with local piston-like flow captures most of the breakthrough curve shape. The later corresponds to pure convection dispersion due to apertures and streamlines geometry distribution.