Compositional Two-Phase Flow in Saturated-Unsaturated Porous Media: Benchmarks for Phase Appearance/Disappearance

Résumé. The two test cases presented herein aimed at simulating the transport migration of nuclides around a nuclear waste repository and belong to the "Two-Phases Numerical Test Data Base" presented in [1], [2]. They were initially designed in the framework of the French research group MoMaS [3]. The starting point in designing all the test cases presented in [1] comes from some of the main challenges the traditional simulators for multiphase flow in porous media are facing when attempting to simulate gas migration in deep geological repositories for long-lived high-level nuclear waste; particularly with low permeability argillites host rocks, as considered by most European radioactive waste management organisations and regulators ( see for instance: [4]). The gas migration in this type of porous media is driven by a compressible two-phase partially miscible flow, and is described by a system of nonlinear parabolic PDE’s (see [5]). The aim of the test-cases presented below and in [1] is to address some of the specific problems encountered when numerically simulating gas migration in such underground nuclear waste repositories. But, because we are interested in the difficulties inherent to physical modeling , and less in the ones coming from numerical methods, we kept in all these test cases a simple geometry corresponding to a quasi 1-D flow. The first test case is motivated by simulating the gas-phase appearance/disappearance in a two-phase flow, produced by injection of H2 in a homogeneous porous medium initially fully saturated with pure water. The aim of the second test case is to simulate the evolution of a compressible and partially miscible two-phase flow, starting from an out of equilibrium initial state, made up of two adjacent partially liquid saturated zones with two different uniform pressures .