  Carbon Capture and Storage (CCS) is a recently discussed new technology,
aimed at allowing an ongoing use of fossil fuels while preventing the produced
CO2 to be released to the atmosphere. CSS can be modeled with two components
(water and CO2) in two phases (liquid and CO2). To simulate the process, a
multiphase flow equation with equilibrium phase exchange is used. One of the
big problems arising in two-phase two-component flow simulations is the
disappearance of the nonwetting phase, which leads to a degeneration of the
equations satisfied by the saturation. A standard choice of primary variables,
which is the pressure of one phase and the saturation of the other phase,
cannot be applied here. We developed a new approach using the pressure of the
nonwetting phase and the capillary pressure as primary variables. One important
advantage of this approach is the fact that we have only one set of primary
variables that can be used for the biphasic as well as the monophasic case. We
implemented this new choice of primary variables in the DUNE simulation
framework and present numerical results for some test cases.
