Horizontal Caverns

Horizontal caverns are an alternative to single or double well caverns for leaching of evaporates (e.g. rock salt and potash) of thin salt layers. A horizontal bore hole is drilled from a deviated vertical borehole into the salt layer for that. The leach string is inserted into the horizontal open bore hole for solvent injection and brine recovery in the annular space.

The model conception postulates that there is a more or less thick porous matrix in front of the dissolution face. This porous matrix is formed by non-soluble residues in the case of non-selective leaching and in the case of selective leaching by non-soluble salts.

A CFD cavern flow model was set up for the numerical simulation of the leaching process in a horizontal cavern using COMSOL Multiphysics®. The model takes into account:

• the density influenced brine flow in the porous matrix and the free flow domain (laminar/turbulent),
• mass transport of multiple salt components with solution kinetics and saturation equilibria,
• the numerical calculation of the fluid density depending on temperature and concentrations of salt components and
• heat transport inside of the cavern and heat exchange with the surrounding rock, considering dissolution heat.

Highly specialised approaches facilitate the economical simulation of the brine flow in horizontal caverns and the analysis of the quasi steady state flow regime. The k-eps-turbulence-model with a buoyancy-induced turbulence is used to simulate turbulent flow. The calculation of the fluid density considers the salt components NaCl, KCl, MgCl₂, Na₂SO₄, K₂SO₄ und MgSO₄.