We are interested in solving systems of conservation laws modeling multiphase fluid flows under the approximation of local thermodynamical equilibrium except at very localized places. This equilibrium occurs for states on sheets of a stratified variety called the "thermodynamical equilibrium variety," obtained from thermodynamical laws. Strong deviation from equilibrium occurs in shocks connecting adjacent sheets of this variety. We assume that fluids may expand and we model the physical problem by a system of equations where a velocity variable appears only in the flux terms, giving rise to a wave with "infinite" characteristic speed. We develop a general theory for fundamental solutions for this class of equations. We study all bifurcation loci, such as coincidence and inflection loci and develop a systematic approach to solve problems described by similar equations. For concreteness, we exhibit the bifurcation theory for a representative system with three equations. We find the complete solution of the Riemann problem for two-phase thermal flow in porous media with two chemical species; to simplify the physics, the liquid phase consists of a single chemical species. We give an example of steam and nitrogen injection into a porous medium, with applications to geothermal energy recovery.
Compositional flow in porous media: Riemann problem for three alkanes
