Abstract
The injection of a reactive fluid into an open fracture may modify the fracture surface locally and create a ramified structure around the injection point. This structure will have a significant impact on the dispersion of the injected fluid due to increased permeability, which will introduce large velocity fluctuations into the fluid. Here, we have injected a fluorescent tracer fluid into a transparent artificial fracture with such a ramified structure. The transparency of the model makes it possible to follow the detailed dispersion of the tracer concentration. The experiments have been compared to two dimensional (2D) computer simulations which include both convective motion and molecular diffusion. A comparison was also performed between the dispersion from an initially ramified dissolution structure and the dispersion from an initially circular region. A significant difference was seen both at small and large length scales. At large length scales, the persistence of the anisotropy of the concentration distribution far from the ramified structure is discussed with reference to some theoretical considerations and comparison with simulations.
Highlights
In both geological systems and industrial fields, fractures are known to be important pathways for fluid transport
We have performed experiments and computer simulations of dispersion in an open fracture with an initial state emerging from a ramified dissolution pattern
The ramified dissolution structures have a significant effect on the local concentration Cn(r) and the concentration averaged over angles < Cn(r) > both for small and large length and time scales
Summary
In both geological systems and industrial fields, fractures are known to be important pathways for fluid transport. The permeability of fractures is significantly higher than the porous matrix, so in many systems fractures play an important role in the fluid transport processes. The flow of tracer particles in a fracture is influenced by both convection and diffusion processes, and the combined effect of these two processes leads to Taylor dispersion. This effect was first studied by Taylor [1] for solvent flowing slowly through a tube. Some previous works consider geometric anisotropy, using self-organized percolation model to study flow through disordered porous media [8,9,10]
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