Density-driven flow and transport in saturated porous media. Salt solute infiltration into Hele-Shaw cells — a comparison between numerical and experimental results

Abstract

Generally, the transport of a dense, miscible, non-reactive fluid (e.g., saltwater) in saturated porous media is described by mass balance equations (fluid and solute), Darcy's law, Fick's law and so-called state equations. In the mixing zone, the density and the dynamic viscosity are highly dependent on solute concentration. This system of equations is solved by combining the mixed hybrid finite element method (MHFEM) and the discontinuous finite element method (DFEM). Tested on standard benchmarks, e.g.: Henry's problem or Elder's problem, these numerical techniques lead to identical or better results than those found in the specialized literature. Consequently, we used this numerical model to simulate the laboratory experiments carried out in a 2D configuration. A salt solute is locally injected into a Hele-Shaw cell. The constant thickness of the aperture between the two plates of the cell represents a constant permeability (homogeneous media). these two plates are transparent (optical glasses) and enable us by optical observations (CCD camera), to analyze the displacement of the salt solute injected in the upper part of the cell. In order to analyse and compare numerical and experimental results, a measuring system based on the light absorption method has been developed. It was validated by a theoretical and experimental analysis of the relation between the CCD output and the concentration. This measuring system has therefore enabled us to detect temporal and spatial distributions of the concentration within a Hele-Shaw cell. The good agreement between the experimental and numerical results means that we will be able to use this experimental system with others flow situations to test the efficiency of numerical predictions.