COMPUTING BRINE TRANSPORT IN POROUS-MEDIA WITH AN ADAPTIVE-GRID METHOD

An adaptive-grid finite-difference method is applied to a model for non-isothermal, coupled flow and transport of brine in porous media. In the vicinity of rock salt formations the salt concentration in the fluid becomes large, giving rise to disparate scales in the salt concentration profiles. A typical situation one encounters is that of a sharp freshwater-saltwater interface that moves in time. In such situations adaptive-grid methods arc more effective than standard fixed-grid methods, since they refine the space grid locally and, hence, provide for substantial reduction in the number of grid points, memory use and CPU time. The adaptive-grid method of this paper is a static, local uniform grid refinement method. Its main feature is that it integrates on nested sequences of locally uniformly refined Cartesian space grids, which are automatically adjusted in time to follow rapid spatial transitions. Variable time steps are used to cope with rapid temporal transitions, including a fast march to possible steady-state solutions. For time stepping, the implicit, second-order BDF scheme is used. Two specific example problems are numerically illustrated. The main physical properties involved here are advection and dispersion and in case of dominant advection sharp freshwater-saltwater interfaces arise.