“…Here we apply the discontinuous Galerkin (DG) IIPG (incomplete interior penalty Galerkin) method for the flow problem to satisfy the discrete sum compatibility condition [21,55,70]. Mathematical stability and error convergence of EG for a single phase system is discussed in [51,52,55] The EG finite element space approximation of the wetting phase pressure p w (x,t) is denoted by P w (x,t) ∈ V EG h,l (T h ) and we let P k w := P w (x,t k ) for time discretization, 0 ≤ k ≤ N. We set an initial condition for the pressure as P 0 w := Π h p w (·, 0). Let p k+1 in , p k+1 out , u k+1 N and f k+1 are approximations of p in (·,t k+1 ), p out (·,t k+1 ), u N (·,t k+1 ) and f (·,t k+1 ) on Γ D , Γ N and Ω, respectively at time t k+1 .…”