Using a multiple-mixing-cell model to study minimum miscibility pressure controlled by thermodynamic equilibrium tie lines

In this work, we demonstrate that our simulation approach, referred to as the multiple-mixing-cell model, gives the same results as the analytical method for two-phase gas flooding. For a gas-oil system with n(c) components, the gas injection process leads to n(c) + 1 constant-composition zones, and the compositional path of the process, i.e., the path in composition space representing the total composition, is controlled by n(c) - 1 key thermodynamic equilibrium tie lines: the initial tie line, the injection tie line, and n(c) - 3 crossover tie lines. In addition, our approach clearly demonstrates that both the gas/oil ratio and fluid mobility do not affect tie-line compositional paths, i.e., compositional paths that lie on the thermodynamic equilibrium tie lines, but they do affect n(c) - 2 non-tie-line compositional paths. Therefore, neither the gas/oil ratio nor the fluid mobility affects the minimum miscibility pressure (MMP). In the context of the multiple-mixing-cell model, this fact has never been explicitly clarified before.