A new way of compositional simulation without phase labeling

Current relative permeability models rely on phase labeling, and cannot accurately capture the effect of compositional variations on relative permeabilities and capillary pressures in enhanced oil recovery (EOR) processes. Discontinuities in flux calculations not only cause serious convergence and stability, but also affects the estimated recovery factor. We developed a fully compositional simulation model using an equation of state (EoS) for relative permeabilities to eliminate the unphysical discontinuities in flux functions caused by phase labeling. In addition, we extended our relative permeability EoS to three phases. The model can capture complex hysteresis effects on three-phase relative permeability. The tuned model is used for simulation of multi-cycle WAG injection. The approach allows for a new search scheme to improve initial estimates for flash calculation. The results show increased robustness of high-resolution compositional simulation for both front calculations (recovery estimates) and convergence of flash algorithms. This paper provides a novel way forward to develop a fully compositional reservoir simulation based solely on continuous and robust equation-of-state relative permeabilities. In addition, this paper provides a detailed analysis of the effects of discontinuous phase labeling on simulation performance and accuracy for 1-D and 2-D water-alternating-gas flooding and three-hydrocarbon-phase flow. The results demonstrate the significant benefits of using an EoS for relative permeabilities.