Finite Element Compositional Reservoir Simulation

Abstract We develop a fully coupled phase-field compositional simulator using an enriched Galerkin (EG) discretization to address key limitations of traditional sequential-implicit workflows in multiphase, multicomponent reservoir simulation. The phase-field framework replaces conventional flash calculations and capillary pressure tables with a Helmholtz free energy formulation, capturing interfacial motion, phase transformation, and multicomponent diffusion through Allen-Cahn and Cahn-Hilliard dynamics. This eliminates the need for local equilibrium constraints and preserves physical coupling between capillarity, diffusion, and flow. The EG method ensures local mass conservation and sharply resolves diffuse interfaces on coarse grids with minimal numerical oscillation, enabling scalable simulations across immiscible, near-miscible, and fully miscible regimes. We implement the method in MOOSE using implicit time integration, adaptive mesh refinement, and Jacobian-free Newton-Krylov solvers. Validation against commercial compositional simulator and SPE benchmark datasets confirms the model's accuracy in capturing recovery dynamics, interfacial migration, and thermodynamic consistency without per-cell flash or empirical capillarity.